A convenient preparation of furo[2,3-b]indoles by conjugated addition of organomagnesium reagents to 2-hydroxyindolylidenemalonates

The chelate-controlled conjugated addition of Grignard reagents to 2-hydroxyindolylidenemalonates was studied as a means of preparing 3a-alkyl-3-methoxycarbonyl-2-oxofuro[2,3-b]indoles in one or two steps. In addition to the alkylorganometallic group variation, the effects of substitution at the aromatic ring on the reaction outcome were established. The indolylidenemalonates were found to be less reactive than the analogous indolylidenecyanoacetates.