Computational insights into cycloadditions of thioisomünchnones with acetylenes: how does sulfur escape from cycloadducts?

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• 作者：Juan Garcí ; a de la Concepció ; n^a ; ^{jugarco@unex.es" class="auth_mail" title="E-mail the corresponding author} ; Martí ; n Á ; valos^a ; Reyes Babiano^a ; Pedro Cintas^a ; ^{pecintas@unex.es" class="auth_mail" title="E-mail the corresponding author} ; José ; L. Jimé ; nez^a ; Mark E. Light^b ; Juan C. Palacios^a
• 关键词：Mesoionic ; Cycloaddition ; Thiazolopyridone ; Thiirane ; Sigmatropic rearrangement
• 刊名：Tetrahedron
• 出版年：2016
• 出版时间：4 August 2016
• 年：2016
• 卷：72
• 期：31
• 页码：4665-4670
• 全文大小：780 K

文摘

The spontaneous loss of sulfur or isocyanate from transient 7-thia-2-azabicyclo[2.2.1]hept-5-en-3-ones, which are initially formed by 1,3-dipolar cycloadditions of thioisomünchnones with acetylenic dipolarophiles, is the key step in the chemoselective syntheses of pyridin-2-ones or thiophenes. The way by which sulfur is released has been the subject of previous studies pointing to a concerted retro-cheletropic mechanism as a more favorable route than the alternative stepwise pathway. The latter however, is apparently prevalent for elimination of isocyanate. Working with a conformationally-restricted bicyclic thioisomünchnone that undergoes facile cycloaddition with acetylenes, sulfur elimination has now been interrogated by experiment and theoretical calculations at the M06-2X and M11 methods in combination with the 6-311++G(d,p) basis set, which unveil rather a sigmatropic shift via the intermediacy of thiirane species. These results provide new vistas and synthetic opportunities in mesoionic cycloadditions.