While 1,3-dipolar cycloadditions have appeared to be a fertile area for research, as attested by the numerous synthetic transformations and resulting applications that have been developed during the past 60 years, the use of neutral three-atom components (TACs) in (3+2) cycloadditions remains comparatively sparse. Neutral TACs, however, have great synthetic potential given that their reaction with a π system can produce zwitterionic cycloadducts that may be manipulated for further chemistry. We report herein that ynamides, a class of carbon π systems that has seen wide interest over the last two decades, can be used as neutral TACs in thermally induced intramolecular (3+2) cycloaddition reactions with alkynes to yield a variety of functionalized pyrroles. The transformation is proposed to occur in a stepwise manner via the intermediacy of a pyrrolium ylide, from which the electron-withdrawing group on the nitrogen atom undergoes an intramolecular 1,2-shift to produce the neutral pyrrole. This work demonstrates a yet unexplored facet of ynamide reactivity with great potential in heterocyclic chemistry.

3+2) cycloaddition reactions are undeniably one of the most robust and versatile synthetic tools in heterocyclic chemistry. The classically required 1,3-dipoles are however limited to three-atom sequences bearing 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 groupings result in zwitterionic (3+2) cycloadducts adaptable to multiple outcomes depending on structure and conditions. Herein, the intramolecular (3 +2) cycloaddition reaction between alkynyl sulfides (neutral TAC) and alkynes to provide key thiophenium ylide intermediates is first reported. These reactive species provide access to highly substituted fused thiophenes following predictable chemical sequences. Structural features on the obtained thiophenes were highly configurable by judicious choice of both alkynyl sulfide substitution and reaction conditions.

(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.

(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.