Asymmetric reductions with chiral reagents from lithium aluminum hydride and (+)-(2S,3R)-4-dimethylamino-3-methyl-1,2-diphenyl-2-butanol

Abstract

Stereoselectivity in reductions of carbonyl compounds by a chiral reagent prepared by adding the amino alcohol (+)-(2S,3ñ)-4-dimethylammo-3-methyl-l,2-diphenyI-2-butanol (6) to lithium aluminum hydride in ether is reasonably high and shows remarkable reversal depending upon age of the reagent from predominantly R product to predominantly S product. Reduction of acetophenone gives either (fi)-(+)or (S)-( -)-methylphenylcarbinol in 80-70% enantiomeric purity depending upon use of the reagent either immediately after its preparation (procedure A) or upon aging overnight or refluxing for a few minutes (procedure B). This reversal in stereoselectivity with age of reagent was observed with five different carbonyl substrates. The reduction of phenyltrifluoromethyl ketone did not show this reversal phenomenon, however. Procedure A for asymmetric reduction of phenyl alkyl ketones gives the R carbinol in excess in each case. Representative enantiomeric purities (% e.e., R isomer

New advances in dual stereocontrol for asymmetric reactions

“…Since the report by Mosher and co-workers in 1972 on the asymmetric reduction of unsymmetrical ketones with stoichiometric chiral alkoxyaluminium hydrides, 10,11 several metalbased methodologies for enantiodivergent catalysis, in which the ligand, the central metal and the reaction conditions can be tuned for this purpose, have been studied. Recently much attention has been paid to study the induction of both enantioselectivities using a single chiral source by changing the reaction conditions.…”

Design, stereoselective synthesis, configurational stability and biological activity of 7-chloro-9-(furan-3-yl)-2,3,3a,4-tetrahydro-1H-benzo[e]pyrrolo[2,1-c][1,2,4]thiadiazine 5,5-dioxide

“…41 In order to obtain (R)-3 the procedure described by Cohen et al and Deeter et al, was applied to 9. [42][43][44]…”

Homo- and heteronuclear 2D NMR approaches to analyse a mixture of deuterated unlike/like stereoisomers using weakly ordering chiral liquid crystals

“…The degree of deuteration was checked by NMR in CDCl 3 /TMS and was found better than 96%. Compound 5 was prepared enantiomerically enriched using the asymmetric reduction method developed by Mosher et al [24].…”