Preparation and C-Alkylation of Enantiomerically Pure S-Phenyl Aziridenecarbothioates. On the Structure of Small-Ring Ester Lithium Enolates

Article abstract of DOI:10.1002/hlca.19870700704

Racemic and enantiomerically pure methyl N-(tert-butyl)-N-benzyl- and N-1-(phenylethyl)aziridinecarboxylates are prepared by known methods and converted to phenyl thioesters (1, 2, 15, 16; Schemes 2 and 3).These are deprotonated with lithium diisopropylamide (LDA) and BuLi (for removal of diisopropylamine) in THF at dry-ice temperature.The resulting lithiated species are surprizingly stable and deuterated, alkylated (CH3, C2H5, allyl, benzyl), and added to aldehydes and nitroolefins in good yields (50-80 percent, 18 examples; Schemes 1 and 4-6).The configurational stability of the lithiated species is studied, and conclusions about their structures are drown.Thus, a C(α)-lithiated ester (see L, Scheme 9) or an O-liithia1ed "enolate" (see M) with pyramidalized C(β)-atom is proposed for species from levorotatory S-phenyl N-benzylaziridinecarbothioate which does not undergo racemization after 1 h at -60 deg C (THF solution).