A new oxindole synthesis

Abstract

A quaternary carbon atom can be set up by irradiation of the N-methylaniline enamine 5 of adamantane-2-carbaldehyde giving the indoline 6 in poor yield. This product was converted into the spiro-oxindole 8, but only in very low yield. Quaternary carbon atoms can be set up more efficiently from the ketone group of adamantanone in two high-yielding steps by conjugate addition of appropriate organometallic carbon nucleophiles to the electrophilic alkenes 9 and 25, obtained by condensation of adamantanone with either Meldrum's acid or nitromethane. By use of the latter intermediate 25, a high yielding, eight-step conversion of adamantanone into the corresponding spiro-oxindole 8 can be carried out. Conjugate addition of triphenylaluminium to the corresponding nitroalkene 33 derived from 2-oxaadamantan-4-one 32 takes place with high stereoselectivity in the sense appropriate for a synthesis of gelsemine, with the phenyl group in the product 34cis to the oxygen bridge.