Synthesis of carba analogs of 6-O-(benzyl)-D-allal- and -D-galactal-derived allyl epoxides and evaluation of the regio- and stereoselective behavior in nucleophilic addition reactions

The new racemic diastereoisomeric epoxides 6α and 6β, the carba analogs of the corresponding d-galactal- and d-allal-derived allyl epoxides have been synthesized and their regio- and stereoselective behavior examined in addition reactions with model O-, C-, N-, and S-nucleophiles. The results have indicated that epoxide 6β has a pronounced tendency toward anti-1,2-addition, whereas epoxide 6α shows interesting levels of syn- and/or anti-1,4-addition processes. A chiral recognition process found with epoxide 6β, turned out to be consistently reduced in epoxide 6α. All the results have been rationalized on the basis of conformational, steric, and stereoelectronic effects.