P(NMe2)3-Mediated Reductive Intramolecular Annulation of Benzoylformates Tethered with a Trisubstituted Alkene Unit and Synthesis of 2,2-Disubstituted 2H-Chromenes.

In this report, a P(NMe2)3-mediated reductive intramolecular annulation reaction has been developed with benzoyl formates bearing a trisubstituted alkene unit. It provides a facile synthesis of highly functionalized 2,2-disubstituted 2H-chromenes with a broad substrate scope and high efficiency. Experimental results suggest this annulation reaction proceeds via a cascade of alkene isomerization/vinyl o-quinone methide formation/6π-electrocyclization. As a key intermediate, the vinyl-substituted o-quinone methide is presumably generated by a Kukhtin-Ramirez adduct initiated O → C vinyl migration.