SYNTHESIS OF MACROCYCLIC ALPHA,BETA-UNSATURATED GAMMA-OXOLACTONES BY RING-ENLARGEMENT REACTIONS - A NEW PATH TO THE MACROCYCLIC LACTONE ANTIBIOTIC-A-26771-B

A new synthetic route to the .alpha.,.beta.-unsaturated .gamma.-oxolactones 2a and 2b, involving two ring-enlargement reactions, is described. Ring opening of bicyclic .alpha.-nitroketones of the type 3 gave ring-enlarged compounds of the type 4 which were converted to monoprotected diketones of the types 10 by using a variation of the Nef reaction as a key step. Macrocyclic lactones of the type 11 were obtained by Baeyer-Villiger oxidation and converted into compounds of the type 2. The conversion of 2b to the macrocyclic lactone antibiotic A 26771 B (1) is already described in the literature.