1,4-Hydrogen shift, thiocarbonyl ylide

In the absence of a dipolarophile, thiocarbonyl ylide 84 undergoes a 1,4-hydrogen shift to give the naphthoannelated thiophene derivative 85. Many examples of related syntheses have been reported (139-143). The photolysis of tetraarylthiiranes in the presence of tetracyanoethene represents an approach to tetrahydrothiophenes via a SET mechanism (75,76). 

The alkylation of (21) with phenacyl or p-bromophenacyl bromide to yield the 1,3-dithiolylium salts (171) offers a more special case. The methylene group of these salts can be deprotonated to form the unstable thiocarbonyl ylides (172) which collapse to the non-isolatable episulfides (175). Further reaction of (175) by loss of sulfur produces (174) whereas episulfide ring-opening and hydrogen shift followed by air oxidation leads to the disulfide (173) (80BCJ2281). 

Scheme 38) <77CL287, 80BCJ2281>. The latter reaction is postulated to proceed via an imstable thiocarbonyl ylide and an episulfide intermediate which suffers loss of sulAir or ring opening and hydrogen shift followed by air oxidation to afford the products <80Ba228i>. 

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