Seyferth’s reagent

Finally, it should be mentioned that from a purely synthetic point of view the reactions involving "transfer" of methylene groups -like the Simmons-Smith reaction [27] or Seyferth s reagents [28]- may be considered formally as cheletropic additions of a [2 + 1] type. 

The Seyferth s reagents (PhHgCX3) are particularly effective for the cyclopropanation of deactivated or base-sensitive substrates, such as allyl halides, allyl isocyanates, and polychloroalkenes (e.g. equation 64) as well as a,j5-unsaturated ketones, esters, nitriles, and sulfones The Michael addition of a trihalomethyl unit has not been observed in this... 

Chemical Modification. Reactions on the macromolecular polyenes were carried out by procedures described previously (3, 4). PhHgCBr3 is obtained by a modification of Seyferth s method (21) from PhHgBr and HCBr3 in presence of a base. Yields similar to those reported in the literature are obtained more easily by replacing the complex (tert-BuOK— tert-BuOH) with a solution of sodium tert-amylate in benzene as prepared by Conia (24). This reagent was, in fact, used systematically in place of potassium tertf-butylate it is easier to use and can be prepared completely free of alcohol. 

The products C are obtained by reduction of products B (X = Br) by Seyferth s method using Bu3SnH at 80°C. (24). This conversion gives yields of more than 95% in the presence of an excess of hydride. The same reaction with B (X = Cl) at 140°C. only results in the reduction of one halogen by using other reagents such as Ph3SnH the same result is obtained, but lower temperatures are possible (i.e., about 100°C.). 

Catalyst-mediated decomposition of diazo compounds in the presence of C=S compounds has found application for the preparation of thiiranes in homogeneous systems (68,110,111). Recently, a convenient procedure for the preparation of geminal dichlorothiiranes from nonenolizable thioketones and chloroform under Makosza conditions was reported (112). Another approach to 2,2-dihalogenated thiiranes (e.g., 2,2-difluoro derivatives) involves the thermolysis of Seyferth reagents in the presence of thioketones (113,114a). Nucleophilic dimethoxycarbene was shown to add smoothly to adamantanethione to provide a unique approach to a thiiranone (5, 5 )-dimethylacetal (114b). 

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