Cycloaddition via Elimination of Small Molecules

In the reported examples of nickel-catalyzed [4 - - 2] or [2 - - 2 - - 2] cycloaddition, the key intermediates are flve-membered heteronickelacycles, which are formed in situ and subsequently converted to six-membered heterocyclic compounds. Thus, a novel and easy route to a new class of heteronickelacycles, [4 + 2] cycloaddition via elimination of small molecules, which involves oxidative addition of heterocycUc compounds to Ni(0) and subsequent elimination of small molecules [Scheme 12.1 (3)], has been reported. 

I- 2] cycloaddition via heteronickelacycle formation by oxidative addition of heterocyclic substrates to Ni(0), followed by elimination of small molecules such as decarbonylation and decarboxylation [replacement of a part of the heterocyclic molecule with Ni(0)]. 

Addition Reactions. While cycloadditions to 6 are still exceedingly rare, reactions of 6 with small molecules, as summarized in Scheme 8.1, were more successful. Treatment of the tetrasilabutadiene with small amounts of water led, via the 1,2-addition product 16 to the rearranged oxatetrasilacyclopentane 17, an analogue of tetrahydrofuran. With an excess of water the tetrasilane-l,4-diol 18 was obtained, which showed no tendency to eliminate water with the formation of 17. ... 

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