Benzyne, generated from 2-carboxybenzenediazonium chloride

Benzyne generated from 2-carboxybenzenediazonium chloride reacted with sulfur monochloiide to give dibenzothiophene 13 (8-10%) and thiantherene 14 (26-35%) (1989SUL83). A mechanism involving the addition of sulfur mono-chloride to benzyne with the formation of betaine 15 followed by the elimination of SCI2 to afford benzothiirene 16 and a further reaction with another benzyne molecule or dimerization to thianthrene 14 is given in Scheme 8. 

Benzyne generated from 2-carboxybenzenediazonium chloride cleaves cyclic and acyclic sulfides, as in the conversion of thiolane 609 to 613. Apparently protonation to the sulfonium salt 612 is faster than cleavage of intermediates 610 and/or 611. 

Styrene oxide and benzyne are reported to give the 1 1 adducts 35 and 36 (9% and 6% yield, respectively), both derived from the same intermediate 34.36 However, propene oxide is apparently unreactive to benzyne, since its use is advocated to react with the hydrogen chloride which is released when benzyne is generated by decomposition of o-carboxybenzenediazonium chloride (Section II,B).37 37a-b... 

If benzyne was generated instead from o-carboxybenzenediazonium chloride in the presence of 108, the remarkable siloxepine 111 was formed (>70%) its structure was confirmed by X-ray diffraction.79 It was shown that the intermediate 1 1 adduct 110 reacts with benzenediazonium-2-car-boxylate (4) at a lower temperature than is required for the decomposition 4 -+ 5 -+ 1 (Scheme 1) this step includes the formation of the strong Si—O bond, and subsequent loss of nitrogen and cyclization lead to 111. The germanium analog of 111 was similarly obtained from 109. 

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