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 [CpTMS 2Y(μ-Me)]2 leads to highly selective cyclization/silylation events. In this process the active catalyst for the reaction, “CpTMS 2YH”, 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 σ-bond metathesis reaction, affording the observed products.