Mechanistic and Preparative Studies of Radical Chain Homolytic Substitution Reactions of N-Heterocyclic Carbene Boranes and Disulfides

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• 作者：Xiangcheng Pan ; Anne-Laure Vallet ; St茅phane Schweizer ; Karim Dahbi ; Bernard Delpech ; Nicolas Blanchard ; Bernadette Graff ; Steven J. Geib ; Dennis P. Curran ; Jacques Lalev茅e ; Emmanuel Lac么te
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：July 17, 2013
• 年：2013
• 卷：135
• 期：28
• 页码：10484-10491
• 全文大小：420K
• 年卷期：v.135,no.28(July 17, 2013)
• ISSN：1520-5126

文摘

Reactions of 1,3-dimethylimidazol-2-ylidene鈥揵orane (diMe-Imd-BH₃) and related NHC鈥揵oranes with diaryl and diheteroaryl disulfides provide diverse NHC鈥揵oryl monosulfides (diMe-Imd-BH₂SAr) and NHC鈥揵oryl disulfides (diMe-Imd-BH(SAr)₂). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC鈥揵orane in the primary NHC鈥揵oryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC鈥揵oryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.