Diazo Transfer Reaction of 2‐(Trimethylsilyl)‐1,3‐dithiane with Tosyl Azide. Carbenic Reactivity of Transient 2‐Diazo‐1,3‐dithiane.

Abstract A novel diazo transfer reaction of 2-lithiated 2-(trimethylsilyl)-1,3-dithiane with tosyl azide in a 1:20 HMPA-THF mixture furnishes 2-diazo-1,3-dithiane 2, which decomposes at about 0°C to give in fairly high yield bis(1,3-dithianylidene) 5 through formal dimerization of derived carbene 4. In the presence of dimethyl fumarate, dimethyl maleate, trans- and cis-1,2-bis(benzenesulfonyl)ethylene, the diazodithiane affords only trans-cyclopropane adducts in a stereoselective, but non stereospecific fashion. With dimethyl acetylenedicarboxylate or 1-tosyl-2-(trimethylsilyl)acetylene, no corresponding cyclopropene adducts are observed, but instead bis(ketene-dithioacetal) products, likely arising from further reaction of cyclopropene intermediates with diazodithiane 2 and/or its carbene 4. A related ring-opened dithioacetal product is observed upon treatment of diazodithiane with dimethyl 3,3-dimethylcyclopropene-1,2-dicarboxylate. The above reactions with electrophilic alkenes and alkynes are preferentially explained in terms of primary intervention of somewhat nucleophilic dithiocarbene 4 rather than its diazo precursor. The outcome of the usual reaction of 2-lithio-2-(trimethylsilyl)-1,3-dithiane with tosyl azide, in the presence of dimethyl acetylenedicarboxylate, is profoundly changed when performed in the absence of HMPA cosolvent. Under these circumstances the occurrence of bis(ketene-dithioacetal) product (and the dimer 5) is essentially suppressed in favor of significant formation of the silylated maleate 12; this is believed to arise from preferential trapping by the alkyne of the triazenyl anion 3, the presumable progenitor of diazodithiane. An X-ray crystallographic analysis of maleate 12 is reported.