Microbial Baeyer-Villiger reaction of bicyclo[3.2.0]heptan-6-ones — a novel approach to sarkomycin A

Abstract

Racemic (1α,2α,5α)- and (1β,2α,5β)-2-bromobicyclo[3.2.0]heptan-6-one ( rac- 7, rac- 10, respectively), (1α,2α,5β)- and (1β,2α,5β)-2-benzyloxybicyclo[3.2.0]heptan-6-one ( rac- 15, rac- 13, respectively), (1β,2α,5β)-2-hydroxy ( rac- 17) and cis-bicyclo[3.2.0]hept-2-en-7-one ( rac- 18) were subjected to a microbial Baeyer-Villiger reaction by Acinetobacter calcoaceticus NCIB 9871. In each case both regioisomeric lactones were formed (67–93 % yield) having always the opposite configuration (20 to > 99 % e.e.). Both the ratio of the regioisomers and the enantiomeric excess proved to be dependent on the type of substitution. Analogously cis-bicyclo[3.2.0.]heptan-2,6-dione ( rac- 1) gave besides other products cyclosarkomycin ( 1b) (7 % yield, 97 % e.e.). Compound 1b was also obtained from the Baeyer-Villiger product of rac- 17 by Swern oxidation (total yield starting from rac- 17 9 %, > 98 % e.e.).