97869-12-0Relevant articles and documents
Diastereoselectivity in the boron aldol reaction of α-alkoxy and α,β-bis-alkoxy methyl ketones
Fernandes, Alessandra A. G.,Leonarczyk, Ives A.,Ferreira, Marco A. B.,Dias, Luiz Carlos
supporting information, p. 3167 - 3180 (2019/03/26)
In this work, using DFT calculations, we investigated the 1,4 and 1,5 asymmetric induction in boron enolate aldol reactions of α-alkoxy and α,β-bisalkoxy methyl ketones. We evaluated the steric influence of alkyl substituents at the α position and the stereoelectronic influence of the oxygen protecting groups at the α and β positions. Theoretical calculations revealed the origins of the 1,4 asymmetric induction in terms of the nature of the β-substituent. The synergistic effect between the α,β-syn and α,β-anti-bisalkoxy stereocenters was elucidated. In the presence of the β-alkoxy center, the reaction proceeds through the Goodman-Paton 1,5-stereoinduction model, experiencing a minor influence of the α-alkoxy center.
Enzymatic Cross-Benzoin-Type Condensation of Aliphatic Aldehydes: Enantioselective Synthesis of 1-Alkyl-1-hydroxypropan-2-ones and 1-Alkyl-1-hydroxybutan-2-ones
Di Carmine, Graziano,Bortolini, Olga,Massi, Alessandro,Müller, Michael,Bernacchia, Giovanni,Fantin, Giancarlo,Ragno, Daniele,Giovannini, Pier Paolo
, p. 4132 - 4141 (2018/09/12)
Benzoin-type reactions have been intensively exploited as a synthetic strategy for the preparation of α-hydroxy ketones. Thiamine diphosphate (ThDP) dependent enzymes are excellent catalysts for asymmetric versions of such reaction types. In particular, in cross-benzoin condensations of aromatic reactants and mixed aromatic/aliphatic reactions, use of these enzymes has resulted in high levels of chemo-, regio- and stereoselectivity. The present work, which confirms this trend for aliphatic reactants, outlines results obtained in the formal cross-benzoin-type condensation of the ‘umpoled’ acetaldehyde and propionaldehyde with various aliphatic aldehydes catalyzed by the ThDP-dependent enzyme acetoin:dichlorophenolindophenol oxidoreductase (Ao:DCPIP OR). In these reactions, 3-hydroxy-3-methylbutan-2-one (methylacetoin) was used as the activated acetaldehyde donor, while 4-hydroxy-4-methylhexan-3-one was employed for the first time as the precursor of activated propionaldehyde. With the exception of 3-hydroxypentan-2-one and 3-hydroxyhexan-2-one, which were obtained in almost racemic form by the condensation of methylacetoin with propanal and butanal, respectively, all other products achieved from reactions performed using the same donor with more hindered aldehyde acceptors were obtained with high conversions (89–99%) and in good to high enantiomeric excess (72–99% ee). In a similar way, high conversions (75–99%) and good ee (76–99%) were observed in reactions performed with the same set of aldehyde acceptors, but using 4-hydroxy-4-methylhexan-3-one as propionyl anion donor. This is the first time that most of the products described herein have been prepared via benzoin-type condensation. (Figure presented.).
Acyclic Stereoselection. 12. Double Stereodifferentiation with Mutual Kinetic Resolution. A Superior Class of Reagents for Control of Cram's Rule Stereoselection in Synthesis of erythro-α-Alkyl-β-hydroxy Carboxylic Acids from Chiral Aldehydes
Heathcock, Clayton H.,Pirrung, Michael C.,Lampe, John,Buse, Charles T.,Young, Steven D.
, p. 2290 - 2300 (2007/10/02)
Chiral α- ketones 7-9 have been prepared and their aldol condesations studied.Compound 8 shows from good to excellent inherent diastereoface selectivity in reactions with achiral aldehydes.Stereoselectivity is related to the size of the alkyl group attached to the aldehyde carbonyl; highest selectivity is observed with diphenylacetaldehyde (>10:1) and pivaldehyde (>19:1).Ketone 8 also shows high diastereoface selectivity in its reactions with chiral, racemic aldehydes 21, 25, 29, and 17, only one stereoisomeric aldol being obtained in each case.Furthermore, the four aforementioned aldehydes show much higher diastereoface selectivity with ketone 8 than they do with the related ketone 1.As a result, the reactions of racemic 8 with these chiral, racemic aldehydes show a high degree of "mutual kinetic resolution".In fact, the rate of the (R)-enolate plus (R)-aldehyde condensation is at least 35 times the rate of the (R)-enolate plus (S)-aldehyde condensation.It is shown by simple logical argument that such mutual kinetic resolution is expected in reactions between two chiral racemic compounds and that the magnitude of the effect should be proportional to the inherent diastereoselectivity shown by each compound in its reaction with achiral reaction partners.Thus, reagents such as 8 can be used to obtain the benefits of double stereodifferentiation even in the racemic form.As an application of the chemistry developed, (+/-)-blastmycinone (47) has been prepared in four steps from ketone 9 (20percent overall yield).
