Catalytic Asymmetric Dearomative 1,3-Dipolar Cycloaddition of 2-Nitrobenzothiophenes and Isatin-Derived Azomethine
Jian-Qiang Zhao1, Shun Zhou1,2, Lei Yang1,2
1Institute for Advanced Study, Chengdu University, Chengdu 610106, China.
Abstract:
An enantioselective dearomative 1,3-dipolar cycloaddition of 2-nitrobenzothiophenes and isatin-derived azomethine ylides with a bifunctional hydrogen-bonding thiourea catalyst was established, giving polyheterocyclic compounds in excellent results (up to 99% yield, >20:1 dr for all cases and up to 99% ee). The enantioselectivity could be reversed by the bifunctional hydrogen-bonding squaramide catalyst containing the same chiral source as in the thiourea catalyst. DFT calculations revealed the origin of the observed stereochemistry and the reversal of enantioselectivity.
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