Synthetic Routes to 3,9-Dimethylidene-1,5,7,11-tetrathiaspiro[5.5]undecane

Spiro orthocarbonates ( SOCs ) have been widely studied, particularly as monomers which on polymerization undergo minimal shrinkage. Of particular interest has been the dimethylidene SOC because, unlike the parent SOC, it is amenable to free-radical polymerization. The incorporation of other hetero atoms, particularly sulfur, into the bicyclic structure offers the potential of polymers with improved refractive indices and mechanical properties. However, whilst literature methods are available for the spiro tetrathioorthocarbonates ( STOCs ),3 the synthesis of a methylidene derivative has not been reported. In this communication we report the synthesis of 3,9-dimethylidene-1,5,7,11-tetra-thiaspiro[5.5] undecane (DMSTOC) (1).