SYNTHETIC STUDIES TOWARDS BRUCEANTIN .1. ESTABLISHMENT OF THE CARBON NETWORK

In a synthetic approach to the biologically active quassinoid bruceantin 1, intermediate 47 was prepared, which contains all required C-atoms, rings A and B, and four of the 10 chiral centers of bruceantin. The possibilities for a convergent strategy were explored, in which a 5-carbon unit would be joined to a 15-carbon unit by three bonds. After the study of various alkylations and Michael additions needed for the key step, it was found that 3-iodo-1-trimethylsilyl-5-hexenyne 44 adds to the dianion of methyl ketone nitriles 3 and 13 chemo-, diastereo-, and enantioselectively.