DIAZO TRANSFER-REACTION OF 2-(TRIMETHYLSILYL)-1,3-DITHIANE WITH TOSYLAZIDE - CARBENIC REACTIVITY OF TRANSIENT 2-DIAZO-1,3-DITHIANE

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 degrees C to give in fair ly high yield bis(1,3-dithianylidene) 5 through formal dimerization of derived carbene 4. In the presence of dimethyl fumarate, dimethyl mal eate, trans- and cis-1,2-bis(benzenesulfonyl)ethylene, the diazodithia ne affords only trans-cyclopropane adducts in a stereoselective, but n on stereospecific fashion. With dimethyl acetylenedicarboxylate or 1-t osyl-2-(trimethylsilyl)acetylene, no corresponding cyclopropene adduct s are observed, bur instead bis(ketene-dithioacetal) products, likely arising from further reaction of cyclopropene intermediates with diazo dithiane 2 and/or its carbene 4. A related ring-opened dithioacetal pr oduct is observed upon treatment of diazodithiane with dimethyl 3,3-di methylcyclopropene-1,2-dicarboxylate. The above reactions with electro philic alkenes and alkynes are preferentially explained in terms of pr imary intervention of somewhat nucleophilic dithiocarbene 4 rather tha n its diazo precursor. The outcome of the usual reaction of 2-lithio-2 -(trimethylsilyl)-1,3-dithiane with tosyl azide, in the presence of di methyl acetylenedicarboxylate, is profoundly changed when performed in the absence of HMPA cosolvent. Under these circumstances the occurren ce of bis(ketene-dithioacetal) product (and the dimer 5) is essentiall y suppressed in favor of significant formation of the silylated maleat e 12; this is believed to arise from preferential trapping by the alky ne of the triazenyl anion 3, the presumable progenitor of diazodithian e. An X-ray crystallographic analysis of maleate 12 is reported. (C) 1 997 Elsevier Science Ltd.