Phosphine-Catalyzed Formal [3 + 2] Annulation of γ-Vinyl Alkynoates with para-Quinamines
Sayan Roy1,2, Amar Sain1,2, Rambabu Chegondi1,2
1Department of Organic Synthesis & Process Chemistry, Council of Scientific and Industrial Research-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500007, India.
Abstract:
We report an unconventional phosphine-catalyzed formal [3 + 2] annulation of a new class of activated 1,4-enynes with para-quinamines, enabling efficient access to cis-hydroindoles bearing stereodefined conjugated dienoate motifs. The transformation proceeds under mild conditions, exhibiting excellent diastereoselectivity and a broad substrate scope. Preliminary asymmetric studies employing chiral phosphine catalysts delivered enantioenriched products with up to 92:8 er. Notably, the protocol is also compatible with para-quinols. Initial mechanistic investigations suggest that the reaction proceeds via a zwitterionic pathway involving remote δ,ε-activation followed by cascade annulation.
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