Aldol Addition
Aldol Reaction
'Aldol' is an abbreviation of aldehyde and alcohol. When the enolate of an aldehyde or a ketone reacts at the α-carbon with the carbonyl of another molecule under basic or acidic conditions to obtain β-hydroxy aldehyde or ketone, this reaction is called Aldol Reaction.
--------------------------------------------------------------------------------
Mechanism
Under conditions of kinetic control, the mixed Aldol Addition can be used to prepare adducts that are otherwise difficult to obtain selectively. This process begins with the irreversible generation of the kinetic enolate, e.g. by employing a sterically hindered lithium amide base such as LDA (lithium diisopropylamide). With an unsymmetrically substituted ketone, such a non-nucleophilic, sterically-demanding, strong base will abstract a proton from the least hindered side. Proton transfer is avoided with lithium enolates at low temperatures in ethereal solvents, so that addition of a second carbonyl partner (ketone or aldehyde) will produce the desired aldol product.
Recent Literature
Highly Enantioselective Organocatalytic Direct Aldol Reaction in an Aqueous Medium
V. Maya, M. Raj, V. K. Singh, Org. Lett., 2007, 9, 2593-2595.
A Highly Efficient Organocatalyst for Direct Aldol Reactions of Ketones with Aldedydes
Z. Tang, Z.-H. Yang, X.-H. Chen, L.-F. Cun, A.-Q. Mi, Y.-Z. Jiang, L.-Z. Gong, J. Am. Chem. Soc., 2005, 127, 9285-9289.
The First Direct and Enantioselective Cross-Aldol Reaction of Aldehydes
A. B. Northtrup, D. W. C. MacMillan, J. Am. Chem. Soc., 2002, 124, 6798-6799.
Highly Diastereo- and Enantioselective Direct Aldol Reactions in Water
Y. Hayashi, T. Sumiya, J. Takahashi, H. Gotoh, T. Urushima, M. Shoji, Angew. Chem. Int. Ed., 2006, 45, 958-961.
Combined Proline-Surfactant Organocatalyst for the Highly Diastereo- and Enantioselective Aqueous Direct Cross-Aldol Reaction of Aldehydes
Y. Hayashi, S. Aratake, T. Okano, J. Takahashi, T. Sumiya, M. Shoji, Angew. Chem. Int. Ed., 2006, 45, 5527-5529.
Chiral Diols: A New Class of Additives for Direct Aldol Reaction Catalyzed by L-Proline
Y. Zhou, Z. Shan, J. Org. Chem., 2006, 71, 9510-9512.
The Aldol Reaction under High-Intensity Ultrasound: A Novel Approach to an Old Reaction
G. Cravotto, A. Demetri, G. M. Nano, G. Palmisano, A. Penoni, S. Tagliapietra, Eur. J. Org. Chem., 2003, 4438-4444.
Reconstructed Hydrotalcite as a Highly Active Heterogeneous Base Catalyst for Carbon-Carbon Bond Formations in the Presence of Water
K. Ebitani, K. Motokura, K. Mori, T. Mizugaki, K. Kaneda, J. Org. Chem., 2006, 71, 5440-5447.
Direct Asymmetric Aldol Reactions of Acetone Using Bimetallic Zinc Catalysts
B. M. Trost, E. R. Silcoff, H. Ito, Org. Lett., 2001, 3, 2497-2500.
Development of Highly Diastereo- and Enantioselective Direct Asymmetric Aldol Reaction of a Glycinate Schiff Base with Aldehydes Catalyzed by Chiral Quaternary Ammonium Salts
T. Ooi, M. Kameda, M. Taniguchi, K. Maruoka, J. Am. Chem. Soc., 2004,126, 9685-9694.
Site Search
any search words
all search words
Main Categories
Organic Reactions Org. Chem. Highlights Abstracts Chemicals Chemistry Tools Chemistry Books Job Market Resources & Suppliers Product of the MonthImprint Sponsors
Tuesday, July 15, 2008
Alder-Ene Reaction
Alder-Ene Reaction
Ene Reaction
The four-electron system including an alkene π-bond and an allylic C-H σ-bond can participate in a pericyclic reaction in which the double bond shifts and new C-H and C-C σ-bonds are formed. This allylic system reacts similarly to a diene in a Diels-Alder Reaction, while in this case the other partner is called an enophile, analogous to the dienophile in the Diels-Alder. The Alder-Ene Reaction requires higher temperatures because of the higher activation energy and stereoelectronic requirement of breaking the allylic C-H σ-bond.
The enophile can also be an aldehyde, ketone or imine, in which case β-hydroxy- or β-aminoolefins are obtained. These compounds may be unstable under the reaction conditions, so that at elevated temperature (>400°C) the reverse reaction takes place - the Retro-Ene Reaction.
While mechanistically different, the Ene reaction can produce a result similar to the Prins Reaction.
--------------------------------------------------------------------------------
Mechanism
Also like the Diels-Alder, some Ene Reactions can be catalyzed by Lewis Acids. Lewis-Acid catalyzed Ene Reactions are not necessarily concerted (for example: Iron(III) Chloride Catalysis of the Acetal-Ene Reaction).
--------------------------------------------------------------------------------
Recent Literature
Formaldehyde Encapsulated in Zeolite: A Long-Lived, Highly Activated One-Carbon Electrophile to Carbonyl-Ene Reactions
T. Okachi, M. Onaka, J. Am. Chem. Soc., 2004, 126, 2306-2307.
Ytterbium(III) Triflate/TMSCl: Efficient Catalyst for Imino Ene Reaction
M. Yamanaka, A. Nishida, M. Nakagawa, Org. Lett., 2000, 2, 159-161.
Steric acceleration of an uncatalysed ene reaction at room temperature
N. Choony, P. G. Sammes, G. Smith, R. Ward, Chem. Commun., 2001, 2062-2063.
Ene Reaction
The four-electron system including an alkene π-bond and an allylic C-H σ-bond can participate in a pericyclic reaction in which the double bond shifts and new C-H and C-C σ-bonds are formed. This allylic system reacts similarly to a diene in a Diels-Alder Reaction, while in this case the other partner is called an enophile, analogous to the dienophile in the Diels-Alder. The Alder-Ene Reaction requires higher temperatures because of the higher activation energy and stereoelectronic requirement of breaking the allylic C-H σ-bond.
The enophile can also be an aldehyde, ketone or imine, in which case β-hydroxy- or β-aminoolefins are obtained. These compounds may be unstable under the reaction conditions, so that at elevated temperature (>400°C) the reverse reaction takes place - the Retro-Ene Reaction.
While mechanistically different, the Ene reaction can produce a result similar to the Prins Reaction.
--------------------------------------------------------------------------------
Mechanism
Also like the Diels-Alder, some Ene Reactions can be catalyzed by Lewis Acids. Lewis-Acid catalyzed Ene Reactions are not necessarily concerted (for example: Iron(III) Chloride Catalysis of the Acetal-Ene Reaction).
--------------------------------------------------------------------------------
Recent Literature
Formaldehyde Encapsulated in Zeolite: A Long-Lived, Highly Activated One-Carbon Electrophile to Carbonyl-Ene Reactions
T. Okachi, M. Onaka, J. Am. Chem. Soc., 2004, 126, 2306-2307.
Ytterbium(III) Triflate/TMSCl: Efficient Catalyst for Imino Ene Reaction
M. Yamanaka, A. Nishida, M. Nakagawa, Org. Lett., 2000, 2, 159-161.
Steric acceleration of an uncatalysed ene reaction at room temperature
N. Choony, P. G. Sammes, G. Smith, R. Ward, Chem. Commun., 2001, 2062-2063.
Acyloin Condensation
Acyloin Condensation
The bimolecular reductive coupling of carboxylic esters by reaction with metallic sodium in an inert solvent under reflux gives an α-hydroxyketone, which is known as an acyloin. This reaction is favoured when R is an alkyl. With longer alkyl chains, higher boiling solvents can be used. The intramolecular version of this reaction has been used extensively to close rings of different sizes, e.g. paracyclophanes or catenanes.
If the reaction is carried out in the presence of a proton donor, such as alcohol, simple reduction of the ester to the alcohol takes place (Bouveault-Blanc Reduction<.
The Benzoin Condensation produces similar products, although with aromatic substituents and under different conditions.
When the acyloin condensation is carried out in the presence of chlorotrimethylsilane, the enediolate intermediate is trapped as the bis-silyl derivative. This can be isolated and subsequently is hydrolysed under acidic condition to the acyloin, which gives a better overall yield.
--------------------------------------------------------------------------------
The bimolecular reductive coupling of carboxylic esters by reaction with metallic sodium in an inert solvent under reflux gives an α-hydroxyketone, which is known as an acyloin. This reaction is favoured when R is an alkyl. With longer alkyl chains, higher boiling solvents can be used. The intramolecular version of this reaction has been used extensively to close rings of different sizes, e.g. paracyclophanes or catenanes.
If the reaction is carried out in the presence of a proton donor, such as alcohol, simple reduction of the ester to the alcohol takes place (Bouveault-Blanc Reduction<.
The Benzoin Condensation produces similar products, although with aromatic substituents and under different conditions.
When the acyloin condensation is carried out in the presence of chlorotrimethylsilane, the enediolate intermediate is trapped as the bis-silyl derivative. This can be isolated and subsequently is hydrolysed under acidic condition to the acyloin, which gives a better overall yield.
--------------------------------------------------------------------------------
Acetoacetic Ester Synthesis
Acetoacetic Ester Synthesis
When α-keto acetic acid is treated with one mole of a base, the methylene group which is more acidic reacts with the base. And the reaction with an alkylation reagent gives alkyl products attached to methylene. When this reaction is repeated in the next step, the other hydrogen can also react to a dialkyl product. The two alkylation agents may be the same or different (R',R'').
β-Keto esters tend to decarboxylate after hydrolysation to β-keto carboxylic acid and heating to give one or two alkyl-substituted ketones, respectively.
If two moles of a base are added in the first step, the hydrogen of the more acidic methylene group, and in the next step the hydrogen of the methyl group (ambident nucleophiles), reacts with the base. The hydrogenated methyl group is, however, more acidic than the hydrogenated methylene group. The reaction with alkylation agent in the following step gives a product substituted at methyl group. This can be synthetically used to prepare selectively ketones of different types.
When α-keto acetic acid is treated with one mole of a base, the methylene group which is more acidic reacts with the base. And the reaction with an alkylation reagent gives alkyl products attached to methylene. When this reaction is repeated in the next step, the other hydrogen can also react to a dialkyl product. The two alkylation agents may be the same or different (R',R'').
β-Keto esters tend to decarboxylate after hydrolysation to β-keto carboxylic acid and heating to give one or two alkyl-substituted ketones, respectively.
If two moles of a base are added in the first step, the hydrogen of the more acidic methylene group, and in the next step the hydrogen of the methyl group (ambident nucleophiles), reacts with the base. The hydrogenated methyl group is, however, more acidic than the hydrogenated methylene group. The reaction with alkylation agent in the following step gives a product substituted at methyl group. This can be synthetically used to prepare selectively ketones of different types.
Acetoacetic-Ester Condensation
The Claisen Condensation between esters containing α-hydrogens, promoted by a base such as sodium ethoxide, affords β-ketoesters. The driving force is the formation of the stabilized anion of the β-keto ester. If two different esters are used, an essentially statistical mixture of all four products is generally obtained, and the preparation does not have high synthetic utility.
However, if one of the ester partners has enolizable α-hydrogens and the other does not (e.g., aromatic esters or carbonates), the mixed reaction (or crossed Claisen) can be synthetically useful. If ketones or nitriles are used as the donor in this condensation reaction, a β-diketone or a β-ketonitrile is obtained, respectively.
The use of stronger bases, e.g. sodium amide or sodium hydride instead of sodium ethoxide, often increases the yield.
The intramolecular version is known as Dieckmann Condensation.
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
However, if one of the ester partners has enolizable α-hydrogens and the other does not (e.g., aromatic esters or carbonates), the mixed reaction (or crossed Claisen) can be synthetically useful. If ketones or nitriles are used as the donor in this condensation reaction, a β-diketone or a β-ketonitrile is obtained, respectively.
The use of stronger bases, e.g. sodium amide or sodium hydride instead of sodium ethoxide, often increases the yield.
The intramolecular version is known as Dieckmann Condensation.
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Monday, June 30, 2008
Tuesday, June 24, 2008
readings
Thursday, September 28, 2000
Goodbye Jerusalem BBC’s correspondent Jeremy Bowen is leaving his Middle East post. Looking back on his years on the job, Bowen gives a personal inside story of Jerusalem – a rarely unbiased account. It is not his war. It is not his land. Bowen merely points to the facts and they speak for themselves. The fate of many Palestinians who ran away or were “driven away” because of an Israeli state that was “created by war” will remain the key source of Israel’s insecurity that will not go away until they make peace. It is a stirring story of a broken people, of the shining Dome of the Rock and the “smelling herbs sold by Palestinian women-mint, basil and zatar”. http://news.bbc.co.uk/hi/english/world/from_our_own_correspondent/newsid_941000/941749.stm
posted by samar at 2:54 PM
Will Traditional Music Rub Shoulders with Globalization? Globalization has brought McDonald’s, Nike and Leonardo Di Caprio to the Middle East. As the concept of the “global village” expands, questions about the place and survival of traditional music arise. Last week, international musicians and music experts put such questions at the First Meeting on the Promotion of Local Music Heritage in the Age of Globalization, which took place in Amman. While some argued that music knows no “religion, country or language, it only knows humanity”, others expressed their belief that “globalization” is just another word for “Americanization”. It only seems more difficult to try and preserve local music and heritage in the overpowering of today’s “homogenous entity”. Last year, Jean Michel Jarre’s millennium concert at the Cairo pyramids proved just that. His ability to fuse Om Kalthoom with western music proved to be a success as a huge audience listened in amazement. http://star.arabia.com/000921/FE4.html
posted by samar at 2:54 PM
Techno Tea What are the Japanese up to now? . Towa Company of Tokyo invented the ‘tea tablet’: super-compressed tea leafs in a heart-shaped mold. According to Towa, the compacted leaf surfaces are protected from air and so should stay fresh longer than normal leaves. It takes up to 4 pills to make a cup of tea, which will cost around 3 English pounds. Maybe someone can call Towa up and ask them for super-compressed alcohol tablets, saving some the hassle of trying to get drunk. http://www.ananova.com/news/story/sm_70158.html
posted by samar at 2:53 PM
O Profligate Youth of Rome, Ye #*!, Ye @#! Harvard University Press, the caretaker and publisher of the Loeb Classic Library, has been putting back the “naughty bits” that have been edited out of Greek and Roman literature. This refers to Plato’s writings on homoerotic love and Aristophanes’ sexually explicit jokes. In the past, translators either replaced the “vulgarities” with decent lines or omitted the scenes. One of Loeb’s translators, Mr. Henderson explains that literal translation of such lines show how the writers used the obscenity to point out the outrageous costumes and expose what was “normally hidden” in their societies. As Emily Katz Anhalt, professor of Classics of at Trinity College explains, “when he (Plato) talks about men being in ‘love’, you shouldn’t translate it as ‘close friends- wink, wink”. As for the students, so far there haven’t been any complains, only a lot of emails asking, “Is this stuff really in there?” http://www.nytimes.com/2000/09/28/arts/28ARTS.html
posted by samar at 2:50 PM
Norms Changing for Women It is not enough to see Arab women smoking cigarettes, shisha, hanging out in bars or in bikinis. Although these might be silent signs for a new change, women in the Middle East are still struggling for independence. The discrimination they face in the work place, in the courts with inheritance claims, honour crimes, divorce and education are some of the issues they have to deal with. According to a United Nations report, 52% of Arab women are still illiterate with a 27% representation in the total workforce. A recent law passed by the Egyptian government making it easer for women to obtain divorces does show a promising future for Arab women. The modernization of their lifestyles is merely a superficial façade where in fact their “battle” still lies ahead. http://www.islamonline.org/iol-english/dowalia/news-2000-sep-28/topnews6.asp
posted by samar at 2:48 PM
You Are What You Wear If only People magazine could get their hands on Mr. Clickwell’s job. Design critic Mr. Clickwell reviews this year’s worst dressed websites. Condemning Salon.com for not using enough ‘curves’, the “red, white and bloated”AOL.com and asking Bill Gates to forget about breaking up the company but rather just “break up this site”, he might seem a bit too harsh. Then again it is almost 2001 and everyone wants something sexy. As for “GO-dot-com” it’s only fair to ask it to just “Go-dot-away.” Click on the site to see for yourself! http://www.islamonline.org/iol-english/dowalia/news-2000-sep-28/topnews6.asp
posted by samar at 2:46 PM
Wednesday, September 27, 2000
blood koran -- comment: oh my god. great story......is this true???
posted by Hana at 6:10 PM
-- the wording for this was a little confusing -- I reworded it : Are you among those of us who are still struggling to set the date and time on our old crummy video players, while others are up and about having three-letter word conversations ? "WAP, DNS, or HTML "...we haven't even caught up on the terminology let alone the technology. Thankfully, the future is looking promising to tech dummies. Apparently, by 2020 we'll be able to talk to our houses. Lights and air conditioners will (flick?) turn on by themselves, refrigerators will refill themselves via online grocery shopping, and our computers will offer us effortless daily medical checkups of blood or bodily waste. As for our cars, all we’ll have to do is sit back and program, while sensors in the car monitor the activities and destination of other vehicles on the road. It may sound like heaven, but it could get complicated-- Let’s just hope they’re working on ‘2020 for Dummies’.
posted by Hana at 6:09 PM
finding the seeds -- great- good flow, well written , interesting - and stereo-type breaking. good.
posted by Hana at 5:48 PM
Finding the Seeds of Hope in a Society of Paradoxes For many Americans the word ‘Iran’ is associated with terrorism, hostage crises and the film “Not Without My Daughter”. Elaine Sciolino’s new book, ‘Persian Mirrors: The Elusive Face of Iran’, depicts a different country. From her 20 years of experience as senior correspondent in the Washington bureau of the New York Times, she gives a true account of the complexity and contradiction of Iranian society today. Sciolino unravels a culture of paradoxes, from segregated parties to a woman who ran a gambling business in her apartment. The success of an expressive cinema against a besieged press, the transformation of the Islamic Republic to an Islamic democracy and the love-hate relationship towards America are all aspects discussed in this ragingly insightful book. http://www.nytimes.com/2000/09/27/arts/27LAPI.html
posted by samar at 2:06 PM
Better
Goodbye Jerusalem BBC’s correspondent Jeremy Bowen is leaving his Middle East post. Looking back on his years on the job, Bowen gives a personal inside story of Jerusalem – a rarely unbiased account. It is not his war. It is not his land. Bowen merely points to the facts and they speak for themselves. The fate of many Palestinians who ran away or were “driven away” because of an Israeli state that was “created by war” will remain the key source of Israel’s insecurity that will not go away until they make peace. It is a stirring story of a broken people, of the shining Dome of the Rock and the “smelling herbs sold by Palestinian women-mint, basil and zatar”. http://news.bbc.co.uk/hi/english/world/from_our_own_correspondent/newsid_941000/941749.stm
posted by samar at 2:54 PM
Will Traditional Music Rub Shoulders with Globalization? Globalization has brought McDonald’s, Nike and Leonardo Di Caprio to the Middle East. As the concept of the “global village” expands, questions about the place and survival of traditional music arise. Last week, international musicians and music experts put such questions at the First Meeting on the Promotion of Local Music Heritage in the Age of Globalization, which took place in Amman. While some argued that music knows no “religion, country or language, it only knows humanity”, others expressed their belief that “globalization” is just another word for “Americanization”. It only seems more difficult to try and preserve local music and heritage in the overpowering of today’s “homogenous entity”. Last year, Jean Michel Jarre’s millennium concert at the Cairo pyramids proved just that. His ability to fuse Om Kalthoom with western music proved to be a success as a huge audience listened in amazement. http://star.arabia.com/000921/FE4.html
posted by samar at 2:54 PM
Techno Tea What are the Japanese up to now? . Towa Company of Tokyo invented the ‘tea tablet’: super-compressed tea leafs in a heart-shaped mold. According to Towa, the compacted leaf surfaces are protected from air and so should stay fresh longer than normal leaves. It takes up to 4 pills to make a cup of tea, which will cost around 3 English pounds. Maybe someone can call Towa up and ask them for super-compressed alcohol tablets, saving some the hassle of trying to get drunk. http://www.ananova.com/news/story/sm_70158.html
posted by samar at 2:53 PM
O Profligate Youth of Rome, Ye #*!, Ye @#! Harvard University Press, the caretaker and publisher of the Loeb Classic Library, has been putting back the “naughty bits” that have been edited out of Greek and Roman literature. This refers to Plato’s writings on homoerotic love and Aristophanes’ sexually explicit jokes. In the past, translators either replaced the “vulgarities” with decent lines or omitted the scenes. One of Loeb’s translators, Mr. Henderson explains that literal translation of such lines show how the writers used the obscenity to point out the outrageous costumes and expose what was “normally hidden” in their societies. As Emily Katz Anhalt, professor of Classics of at Trinity College explains, “when he (Plato) talks about men being in ‘love’, you shouldn’t translate it as ‘close friends- wink, wink”. As for the students, so far there haven’t been any complains, only a lot of emails asking, “Is this stuff really in there?” http://www.nytimes.com/2000/09/28/arts/28ARTS.html
posted by samar at 2:50 PM
Norms Changing for Women It is not enough to see Arab women smoking cigarettes, shisha, hanging out in bars or in bikinis. Although these might be silent signs for a new change, women in the Middle East are still struggling for independence. The discrimination they face in the work place, in the courts with inheritance claims, honour crimes, divorce and education are some of the issues they have to deal with. According to a United Nations report, 52% of Arab women are still illiterate with a 27% representation in the total workforce. A recent law passed by the Egyptian government making it easer for women to obtain divorces does show a promising future for Arab women. The modernization of their lifestyles is merely a superficial façade where in fact their “battle” still lies ahead. http://www.islamonline.org/iol-english/dowalia/news-2000-sep-28/topnews6.asp
posted by samar at 2:48 PM
You Are What You Wear If only People magazine could get their hands on Mr. Clickwell’s job. Design critic Mr. Clickwell reviews this year’s worst dressed websites. Condemning Salon.com for not using enough ‘curves’, the “red, white and bloated”AOL.com and asking Bill Gates to forget about breaking up the company but rather just “break up this site”, he might seem a bit too harsh. Then again it is almost 2001 and everyone wants something sexy. As for “GO-dot-com” it’s only fair to ask it to just “Go-dot-away.” Click on the site to see for yourself! http://www.islamonline.org/iol-english/dowalia/news-2000-sep-28/topnews6.asp
posted by samar at 2:46 PM
Wednesday, September 27, 2000
blood koran -- comment: oh my god. great story......is this true???
posted by Hana at 6:10 PM
-- the wording for this was a little confusing -- I reworded it : Are you among those of us who are still struggling to set the date and time on our old crummy video players, while others are up and about having three-letter word conversations ? "WAP, DNS, or HTML "...we haven't even caught up on the terminology let alone the technology. Thankfully, the future is looking promising to tech dummies. Apparently, by 2020 we'll be able to talk to our houses. Lights and air conditioners will (flick?) turn on by themselves, refrigerators will refill themselves via online grocery shopping, and our computers will offer us effortless daily medical checkups of blood or bodily waste. As for our cars, all we’ll have to do is sit back and program, while sensors in the car monitor the activities and destination of other vehicles on the road. It may sound like heaven, but it could get complicated-- Let’s just hope they’re working on ‘2020 for Dummies’.
posted by Hana at 6:09 PM
finding the seeds -- great- good flow, well written , interesting - and stereo-type breaking. good.
posted by Hana at 5:48 PM
Finding the Seeds of Hope in a Society of Paradoxes For many Americans the word ‘Iran’ is associated with terrorism, hostage crises and the film “Not Without My Daughter”. Elaine Sciolino’s new book, ‘Persian Mirrors: The Elusive Face of Iran’, depicts a different country. From her 20 years of experience as senior correspondent in the Washington bureau of the New York Times, she gives a true account of the complexity and contradiction of Iranian society today. Sciolino unravels a culture of paradoxes, from segregated parties to a woman who ran a gambling business in her apartment. The success of an expressive cinema against a besieged press, the transformation of the Islamic Republic to an Islamic democracy and the love-hate relationship towards America are all aspects discussed in this ragingly insightful book. http://www.nytimes.com/2000/09/27/arts/27LAPI.html
posted by samar at 2:06 PM
Better
Subscribe to:
Posts (Atom)
Posts
