The triplet state of deprotonated mesoionic carbene Breslow intermediates is thermally accessible: Distal difunctionalization of aldehydes
The triplet state of deprotonated mesoionic carbene Breslow intermediates is thermally accessible: Distal difunctionalization of aldehydes
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DOI：
10.1016/j.checat.2022.09.047
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发表时间：
2022-10
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通讯作者：
Zengyu Zhang;Shiqing Huang;Chen-Yuan Li;Liang L. Zhao;Wei Liu;M. Melaimi;G. Bertrand;Xiaoyu Yan
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文献类型：
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作者：
Zengyu Zhang;Shiqing Huang;Chen-Yuan Li;Liang L. Zhao;Wei Liu;M. Melaimi;G. Bertrand;Xiaoyu Yan
N-杂环卡宾（NHC）催化的电子对转移反应在过去的几十年里得到了显著的发展，特别是通过Breslow中间体（BI）对醛类化合物的催化转化。BI在单电子转移（SET）途径中的作用在生物合成中早已确立，在过去的十年中，它被扩展到NHC有机催化。在这里，我们报告说，去质子化的mesoionic卡宾BI（BI-S）有一个惊人的小的单重态/三重态（S/T）的差距只有4.0千卡/摩尔，导致在一个热可访问的三重态。这种低激发态允许通过双自由基过程的芳基醛的一系列远端双官能化。在甲酰基侧，氧化酯化反应伴随着芳基侧的还原发生。在这里，三种类型的化学转化被证明：氢（氘）去官能化，氢化，还原烷基化。
N-Heterocyclic carbene (NHC)-catalyzed transformations through electron-pair-transfer processes have witnessed remarkable developments in the past decades, especially the umpolung of aldehydes via the Breslow intermediates (BIs). The role of BIs in single-electron transfer (SET) pathways has long been established in biosynthesis, and in the last decade, it was extended to NHC organocatalysis. Here, we report that deprotonated mesoionic carbene BIs (BI-s) have an astonishing small singlet/triplet (S/T) gap of only 4.0 kcal/mol, resulting in a thermally accessible triplet state. This low-lying excited state allows for a series of distal difunctionalizations of aryl aldehydes via biradical processes. At the formyl side, an oxidative esterification reaction takes place concomitantly with a reduction of the aryl side. Here, three types of chemical transformation are demonstrated: hydro(deutero)defunctionalization, hydrogenation, and reductive alkylation.