Atom transfer radical cyclization (ATRC) applied to a chemoenzymatic synthesis of Quercus lactones

Abstract

The natural fragrances (+)- trans whisky lactone 2 and (+)- trans cognac lactone 4, together with a minor amount of their (−)- cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (±)- 5 and 1-octen-3-ol (±)- 6. The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (±)- 7 and (±)- 8 into the corresponding homochiral (+)- 7 and (+)- 8, combined with their cyclization under a transition metal catalyzed atom transfer process.