Transformation of 5-Hydroxy- to (5-Chloropentanoyl)amino Derivatives under ‘Direct Amide Cyclization’ Conditions

Abstract

The application of the ‘direct amide cyclization’ conditions to the linear delta-hydroxy diamide 11 is described (Scheme 3). Instead of the cyclization to the expected nine-membered cyclodepsipeptide, only the chloro acid 12 was obtained. Its formation could be explained by consecutive formation of the 1,3-oxazol-5(4H)-one 16 and the six-membered imino lactone 17 as intermediates (Scheme 4). The spontaneous isomerization of the latter gave 12 in a good yield.