The Synthetic Potential of Thiophenium Ylide Cycloadducts

Abstract

(3+2) cycloaddition reactions are undeniably one of the most robust and versatily synthetic tool in heterocyclic chemis-try. The classical 1,3-dipolar cycloaddition, which uses 1,3-dipoles, are however limited to three-atom sequences demonstrating stabilized formal charges in their Lewis structure. The scope of three-atom groupings possible in (3+2) cycloadditions can be greatly expanded by taking of advantage neutral three-atom components (TACs). These also pro-vide an additional degree of chemical possibilities by resulting in zwitterionic (3+2) cycloadducts adaptable to multiple outcomes depending on structure and conditions. In this article, the intramolecular (3+2) cycloaddition reaction between alkynyl sulfides (neutral TAC) and alkynes to provide key thiophenium ylide intermediates is first reported. These highly reactive intermediates provide access to highly substituted fused thiophenes following predictable chemical sequences. Structural features on the obtained thiophenes was found to be highly configurable by judicious choice of both alkynyl sulfide substitution and reaction conditions.