Enantiomerically Enriched α-Methyl Amino Acids. Use of an Acyclic, Chiral Alanine-Derived Dianion with a High Diastereofacial Bias.

ABSTRACT: Hindered esters derived from N-benzoylalanine and the following chiral alcohols have been synthesized: (1) (-)-isopinocampheol; (2) (-)-trans-2-phenylcyclohexanol and (3) (-)-8-phenylmenthol. Sequential treatment of these esters with LDA (1.2 equiv.) and n-butyllithium (2.4 equiv.) at -78°C in THF generates the corresponding chiral dianions. Alkylation of each of these with benzyl bromide reveals that only the (-)-8-phenylmenthyl auxiliary confers a high diastereofacial bias upon its derivative dianion. In fact, that dianion (6) consistently displays diastereomeric ratios in the range of 89:11 to 94:6 for alkylations with a spectrum of nine alkyl halides. If one recrystallization step is included, a single diastereomeric product may be obtained, as is demonstrated for

SUBMITTER: Berkowitz DB 

PROVIDER: S-EPMC6020834 | biostudies-literature | 1995 Mar

REPOSITORIES: biostudies-literature