SYNTHESIS OF C-2 FUNCTIONALIZED 1,6,8-TRIOXADISPIRO[4.1.5.3]PENTADEC-13-ENES

The syntheses of bis-spiroacetals 28 and 44, model systems for the tri cyclic bis-spiroacetal moiety of the polyether antibiotic epi-17-deoxy -(O-8)-salinomycin 3, are described. Introduction of an aldehyde group at C-2 was necessary for further elaboration of the right hand side o f the molecule. It was found that the choice of protecting group on th e hydroxymethyl substituent (precursor to an aldehyde group) was cruci al to the outcome of the key oxidative cyclisation.