Cycloaddition profile of pentafulvenes with 3-oxidopyrylium betaine: experimental and theoretical investigations

abstract A detailed investigation on the effect of solvent polarity, temperature, and microwave irradiation onperiselectivity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaine is described.The base catalyzed generation of 3-oxidopyrylium betaine in CHCl 3 resulted in the exclusive formation of[6þ3] adducts. With increase in solvent polarity and temperature, mixtures of [6þ3] and [3þ2] adductswere formed, where as under microwave irradiation, [3þ2] adducts were formed exclusively. Theexperimental results have been rationalized on the basis of theoretical calculations. 2013 Elsevier Ltd. All rights reserved. 1. IntroductionPentafulvenes have invoked considerable interest in organicsynthesisduetotheirexcellentreactivityincycloadditionreactionsand the versatility of the reaction products. 1 They perform flexiblyas 2 p , 2 4 p 3 or 6 p 4 candidates in cycloaddition reactions and havebeen identified asthewell knownconstruction unit for many fusedring systems through intra- and intermolecular cycloaddition re-actions.