Substrate-dependent regiodivergence in [3 + 2] annulation reactions of 2-(phenacylethylidene)cyclobutanones with thioureas

Barranco S.;Pagnanini A.;Cuccu F.;Caboni P.;Guillot R.;Aitken D. J.;Frongia A.

2024-01-01

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Abstract

The [3 + 2] annulation reaction between a thiourea, an ambident dinucleophile, and a 2-(phenacylethylidene)cyclobutanone, containing a novel pull-pull alkene system, could in principle proceed with several chemo- and regioselectivity profiles. Here we describe a convenient synthesis of the functionalized cyclobutanone substrates and show that they react with thioureas in a manner that is rationalized mechanistically in terms of the steric and electronic effects at play. The [3 + 2] annulation proceeds in mild, additive-free conditions to provide access to previously unknown cyclobutane-fused imidazolidine-2-thione and thiazolidine-2-imine derivatives in good yields.We report here a successful synthesis of previously unknown cyclobutane-fused imidazolidine-2-thione and thiazolidine-2-imine derivatives in good to high yields.