ENANTIOSELECTIVE CYCLOADDITION VIA A CHIRAL KETO-ESTER KETENE EQUIVALENT

The synthesis and cycloaddition -benzoxathiolan-(Z)-2-carbomethoxyprop enyl-3-oxide (1) with cyclopentadiene is described. This procedure all ows the direct synthesis of useful enantiopure building blocks such as (+)-(1R,4R)-bicyclo[2.2.l]hept-5-en-2-one (2) and the precursor ketoe ster 11. Cycloaddition, at -78 degrees C in the presence of BCl3, proc eeded with complete pi-facial preference syn to the sulfoxide lone pai r of the dienophile 1.