Trial Application of MM_2 Values to the Interpretation of Different Behaviors Between Grignard and Corresponding Organolithium Reagents in Streoselective Aldol-type Conden-sation of Ketones with Acetates for Asymmetric Syntheses of 3-Hydroxy-3-Phenylester

概要

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In order to understand the stereochemistry of aldol-type condensation of ketones with chiral acetates as quantitatively as possible, an attempt was carried out to apply MM2 to a model consisting of cisoid and transoid transition states on two carbonyl groups of ketone and acetate origins. In the model, as an analogical substituent of metallic moieties, 2,4,6-trioxanylethylidene group was temporarily used, and cyclohexa-1,3,5-triene was used instead of the benzene ring.　In preliminary MM2 calculations for checking the validity of the 1atter, no bad evidence was found in these calculations in the case of comparisons between l,4- and l,6-di-tert-butylcycloocta-1,3,5,7-tetraenes, as well as among conformers of l,3,5-trineopentylbenzene.　When a chiral acetate was (R)-(+)-2-cyclohexylethyl acetate (III), preferred enantiomers yielded by reactions of acetophenone by means of diethylaminomagnesium bromide and diethylaminolithium (and subsequent hydrolysis and esterification with diazomethane) were (R)-(-) and (S) -(+)-methyl 3-hydroxy-3-phenylbutyrates (I), respectively, whereas in cases of (R)-(+)-1-phenylethyl acetate (II), only (S)-I was obtained irrespectively of the two reagents. When the cisoid and transoid were mainly applied to transition states from Grignard and organolithium reagents, respectively, the trends of MM2 values matched with those of the directions of the observed asymmetric induction.
山形大学の論文
1990-01-20