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) leads to highly selective cyclization/silylation events. In this process the active catalyst for the reaction, "(Cp2YH)-Y-TMS", undergoes initial olefin insertion at the vinyl group. Even isopropenyl substituents on the heteroaromatics react in preference to less sterically encumbered allyl groups. Furthermore, the observed regioselectivity reflects an "aryl-directed" process, whereby the more highly substituted secondary or tertiary organometallic is initially generated. This intermediate undergoes cyclization onto the remaining alkene and subsequent silylation by a sigma-bond metathesis reaction, affording the observed products.