Local Conformer Effects in Unsaturated Lactones

Article abstract of DOI:10.1021/ja00252a021

Allylic unsaturated lactones 5E and 5Z can be epoxidized and osmylated with useful stereocontrol.The epoxidations follow the pattern predicted from evaluation of local conformer effects, and epoxides 8 and 14 are favored.These products correspond to peripheral attack on the exposed olefin face of conformers similar to 1 (Z-alkene) or 2 (E-alkene).As in the case of simple carbocyclic alkenes, osmylation of the Z-isomer (5Z) follows the same selectivity pattern as the epoxidation, and 16 is the major diol.However, the isomeric 5E is osmylated from the opposite olefin face compared to the epoxidation and gives 13 as the major diol.The analysis of epoxidations by the local conformer approach is compared with the results of molecular mechanics (MACROMODEL) evaluations of the favored conformers of 5E and 5Z and of the derived epoxides.