Heteroallenes dimerization

Experiments reported in 1982 " by tbe same group provided the first example of heteroallene dimerization. In this work, head-to-head dimerization of 1-silaallenes lla-c (Scheme 4) was observed, forming 1,2-disilacyclobutanes 12a-c with two exocyclic double bonds. 

In contrast to a head-to-tail bis(heteroallene) dimer intermediate, as is found for the metal-promoted disproportionation of several heteroallenes (see CS2), a mechanism via an tj1 intermediate and (23) is suggested for reaction (8). Reaction (9) is also thought to proceed via an t -COS intermediate.31 Apparently, although C—S bond cleavage occurs in the transition metal chemistry of CS2, it is more important in the transition metal chemistry of COS.3... 

Coordinated CS2 groups can react via dimerization and abstraction of CS2, as can be seen in a survey of reactions of a rhodium(I) phosphine complex with CS2 (Scheme 1). The dimerization can be throught to proceed through a nucleophilic attack on the carbon atom of CS2 via an end-on intermediate of the heteroallene fragment.1011... 

Becker, who intensively studied the anodic oxidation of heteroallenes, showed that electrooxidation of aryl-substituted ketene imines leads to mono- and multiannulated heterocyclic dimers [139]. 

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