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On the preparation of β‐amino acids from α‐amino acids using the Arndt‐Eistert reaction: Scope, limitations and stereoselectivity. Application to carbohydrate peptidation. Stereoselective α‐alkylations of some β‐amino acids

1995; Wiley; Volume: 1995; Issue: 7 Linguagem: Inglês

10.1002/jlac.1995199507163

0947-3440

Joachim Podlech, Dieter Seebàch,

Cyclopropane Reaction Mechanisms

Abstract The Arndt‐Eistert homologation of α‐amino acids was studied to determine the stereoselectivity in this reaction by chromatographic up‐to‐date analytical methods. While carba‐mate‐protected phenylglycine was transformed to the corresponding β‐amino acid methyl ester with a stereoselectivity of only 9:1, all other tested amino acid derivatives (Ala, Phe, Ser, Orn, tert ‐Leu and perhydro‐azepine‐2‐carboxylic acid, suitably protected) were homologated with full retention of configuration (products 9–17 ). The intermediate diazo ketones 1–8 were purified and characterized by their NMR spectra. When nucleophiles derived from partially protected sugars were present during decomposition of the diazo ketones (derived from amino acids or dipeptides), a strong dependence of the yield (products 21–24 ) on the degree of steric hindrance of the nucleophilic OH group was observed. Two of the β‐amino acids obtained from the homologation reaction were transformed to α‐substituted ( 25–27, 31, 32 ) and α,α‐disubstituted β‐amino acid derivatives ( 28, 29 ) with excellent selectivities (in most cases, a single diastereoisomer was obtained).