Enantioselective Cyclopropanation/[1,5]-Hydrogen Shift to Access Rauhut-Currier Product

Reactivity of quinone methides with carbenes generated from α-diazocarbonyl compounds and related compounds

Over the years, quinone methides have broadly been applied in synthesis and biological systems for synthesizing heterocyclic compounds and biologically active molecules. In this feature article, we have discussed the novel and uncovered reactivity of o-quinone methides, p-quinone methides, aza-o-quinone methides, and indolyl-2-methides with carbenes generated from α-diazocarbonyl compounds and related compounds. Two in situ-generated transient intermediates undergo cycloannulation reactions, metathesis-type reactions, 1,6-conjugate addition reactions, cyclopropanation reactions, and many other transformations to access nitrogen- and oxygen-containing heterocyclic compounds and beyond. The reactivity of quinone methides and carbenes is observed in various metal catalysts, Brønsted-acids, Lewis acids, phase transfer catalysts, additives, and visible-light-induced transformations.

Enantioselective Friedel-Crafts Alkylation of Furans with o-Quinone Methide Using a Chiral Oxazaborolidinium Ion Catalyst

A chiral Lewis acid-catalyzed enantioselective Friedel-Crafts furan alkylation with in situ-generated o-quinone methides has been developed. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction proceeded in high yield (up to 99%) with excellent enantioselectivity (up to >99% ee).

Synthesis of Dihydrochromeno[2,3-b]indoles via an Fe(OTf)3-Catalyzed Cascade Reaction

A tandem cyclization between 2-(2-aminophenyl)acetonitriles and 2-(hydroxy(aryl)methyl)phenols for the preparation of dihydrochromeno[2,3-b]indole derivatives was successfully developed. The transformation proceeded smoothly in the presence of a catalytic environmentally benign iron salt, and various multisubstituted dihydrochromeno[2,3-b]indoles were synthesized in moderate to high yields.