Organoyttrium-catalyzed sequential cyclization/silylation reactions of nitrogen-heteroaromatic dienes demonstrating "aryl-directed" regioselectivity

The reaction of 1-allyl-2-vinyl-1H-pyrroles and 1-allyl-2-vinyl-1H-indoles with arylsilanes in the presence of catalytic [(Cp2Y)-Y-TMS(mu-Me)](2) lead s to highly selective cyclization/silylation events. In this process the ac tive catalyst for the reaction, "(Cp2YH)-Y-TMS", undergoes initial olefin i nsertion at the vinyl group. Even isopropenyl substituents on the heteroaro matics react in preference to less sterically encumbered allyl groups. Furt hermore, the observed regioselectivity reflects an "aryl-directed" process, whereby the more highly substituted secondary or tertiary organometallic i s initially generated. This intermediate undergoes cyclization onto the rem aining alkene and subsequent silylation by a sigma-bond metathesis reaction , affording the observed products.