5-endo-trig Cyclization 4+2 Cycloaddition reactions

The cr-alkenylpalladium 400, formed as an intermediate, is converted into the benzene derivative 401 by the intermolecular insertion of acrylate[278], A formal [2 + 2 + 2] cycloaddition takes place by the reaction of 2-iodonitroben-zene with the 1,6-enyne 402. The neopentylpalladium intermediate 403 undergoes 6-endo-trig cyclization on to the aromatic ring to give 404[279]. 

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