Radialenes, rearrangement

A polycyclic system with a l,3-dioxa-2-silacyclohepta-4,6-diene fragment was obtained in low yield from bis(diazocarbonyl)silane 671. In the first stage, a biscarbene or a biscarbenoid, generated in the presence of copper triflate or palladium acetate, forms 1,2-diacylcyclopropene, then rearranging into cyclic cumulene triene 672 by migration of a silicon atom to an oxygen atom. The latter dimerizes to [4]-radialen 673 or reacts with furan to afford 674 (Scheme 32) (89AG175()). 

While nickel catalysts cyclize 2,5-dimethyl-2,3,4-hexatriene to give octamethy/1-[4]-radialene, [CpCo(C2H4)2] under ethylene pressure gives a 1 1 codimerization product see equation (48). The [4]-radialene is rearranged by the catalyst to a benzene derivative, probably via cobalt 7r-allyl intermediates. ... 

Phosphabutatrienes react with dichlorocarbene and the initial cycloadducts 15 rearrange to give the isolated phospha[3]radialenes 16. ... 

Surprisingly little is known about the coordination chemistry of [4]radialenes. The interaction of octamethyl[4]radialene (71) with CpCo(ii -CH2=CH2)2 may begin with the formation of a diene complex CpCo(ii -71), but it continues as a catalytic rearrangement to finally furnish 1,3-diisopropyl-5-methyl-2-(l-methylvinyl)benzene [81]. 

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