Asymmetric conjugate additions of chiral allyl- and crotylphosphonamide anions to .alpha.,.beta.-unsaturated carbonyl compounds: highly stereocontrolled access to vicinally substituted carbon centers and chemically asymmetrized chirons
摘要:
Reactions of anions derived from chiral nonracemic allyl and crotyl bicyclic phosphonamides with alpha,beta-unsaturated cyclic ketones, esters, lactones, and lactams take place at the gamma-position of the reagents and lead to diastereomerically pure or highly enriched products of conjugate addition. The option to quench the corresponding enolates with various alkyl halides offers a versatile approach to vicinal substitution including the generation of quaternary carbon centers.
Combined Synthetic/CD Strategy for the Stereochemical Assignment of the Tricarballylic Acid Side Chains of Fumonisin B<sub>1</sub>
作者:Michaela Hartl、Hans-Ulrich Humpf
DOI:10.1021/jo0000630
日期:2001.6.1
The circulardichroism (CD) excitonchiralitymethod was employed for the stereochemical assignment of the tricarballylic acid (TCA) side chains of fumonisin B(1) 1a (FB(1)). Using 2-naphthoate for chromophoric derivatization of the reduced TCA moieties, the absoluteconfiguration was shown to be R. For additional confirmation, an optically active dihydroxy-tert-butanoate 2 related to the TCA group