title: Unusual intramolecular [2 + 2] cycloaddition of allyl and vinylidene C=C bonds under mild conditions: a theoretical analysis.
abstract: A theoretical analysis allows for the rationalization of the recently reported unusual formation under mild conditions of a cyclobutylidene ring from a diastereoselective [2 + 2] intramolecular cycloaddition of two C=C systems. The reaction takes place by heating in dichloromethane the vinylidene complexes [Ru((eta(5),eta(3)-C(9)H(7))[=C=C(R)H][kappa(1)-(P)-PPh(2)(C(3)H(5))](PPh(3))][BF(4)] (R = Ph, p-Me-C(6)H(4)) (1) yielding the bicyclic alkylidene complexes [Ru((eta(5),eta(3)-C(9)H(7))[kappa(2)-(P,C)-(=CC(R)HCH(2)CHCH(2)-PPh(2)](PPh(3))][BF(4)] (2). The proposed mechanism represents an alternative to the classical Woodward-Hoffmann's supra-antara approach.
authors.affiliation: Laboratorio de Química Computacional, Instituto de Química Organometálica Enrique Moles (Unidad asociada al CSIC), Facultad de Química, Universidad de Oviedo, Julián Clavería 8, 33006, Oviedo, Principado de Asturias, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Braña
authors.forename: José
authors.initials: J
authors.lastname: Gimeno
authors.forename: José A
authors.initials: JA
authors.lastname: Sordo