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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… Click to show full 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.
Journal Title: Organic letters
Year Published: 2021
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