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RESEARCH PRODUCT

Understanding the formation of [3+2] and [2+4] cycloadducts in the Lewis acid catalysed reaction between methyl glyoxylate oxime and cyclopentadiene: a theoretical study

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The formation of the formal [3+2] and [2+4] cycloadducts in the Lewis acid (LA) catalysed reaction of cyclopentadiene (Cp, 1) with methyl glyoxylate oxime (MGO, 2a) has been theoretically studied using DFT methods. Coordination of BF3 LA to the oxygen atom of MGO 2a not only increases the electrophilicity of the oxime, but also makes the corresponding tautomeric BF3:nitrone complex 8b the reactive species. The reaction is characterised by the nucleophilic attack of Cp 1 on the carbon atom of the corresponding BF3:nitrone complex 8b. The subsequent ring closure at the end of the reaction allows the formation of the [3+2] or [2+4] cycloadducts. ELF bonding analysis of selected points on the intrinsic reaction coordinate of the two competitive endo paths enables us to establish that the formation of the formal [3+2] or [2+4] cycloadducts takes place through stereoisomeric transition state structures with a similar electronic structure.