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Organoyttrium-catalyzed sequential Cyclization/Silylation reactions of nitrogen-heteroaromatic dienes demonstrating
1Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
Abstract:
The reaction of 1-allyl-2-vinyl-1H-pyrroles and 1-allyl-2-vinyl-1H-indoles with arylsilanes in the presence of catalytic [Cp(TMS)(2)Y(&mgr;-Me)](2) leads to highly selective cyclization/silylation events. In this process the active catalyst for the reaction, "Cp(TMS)(2)YH", 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.