BAKER'S YEAST REDUCTION OF CYCLIC DELTA-KETOESTERS.SYNTHESIS AND CHIROPTICAL PROPERTIES OF CONDENSED DELTA-LACTONES

Enantiomerically pure condensed delta-lactones have been prepared from the corresponding delta-ketoesters by the use of Saccharomyces cerevisiae. The reactions were not only highly enantioselective but also highly diastereoselective, provided the baker's yeast was preincubated at 50 degrees C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.