Alkylsilver intermediate

From a mechanistic perspective, the reaction is similar to those described above. Silver-catalyzed cyclization of the ketone to the allene gave a cyclic oxonium intermediate. A [1,2]- or [1,5]-alkyl shift modified the sigma skeleton leading to an alkylsilver intermediate, which on elimination gave a trisubstituted furan. 

According to this postulate, the difference between coupling with silver and disproportionation with iron rests on the decomposition of the alkylmetal intermediate in Equation 50. Indeed, it has been shown separately in Equation 42 that the decomposition of alkylsilver(I) proceeds by reductive coupling. Unfortunately, the highly unstable alkyliron intermediate in Scheme 6 is not yet accessible to independent study, but the somewhat analogous dialkylmanganese(ll) species in Equation 51 undergoes similar reductive disproportionation by a mechanism S) reminiscent of dialkylplatinum(ll) complexes described in Equation 7. 

Other transmetallation reactions of silver halides or their complexes with phosphine ligands (e.g. [AgIP(Bu-w)3]) with alkylhthium and alkylmagnesium reagents confirm the fleeting stability of the alkylsilver compounds. In each case the composition of the AgR intermediates has been derived from the analysis of the products formed in their thermal decomposition. So far, representatives of the class of simple alkylsilver complexes have not been isolated in pure form. 

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