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Enantioselective Synthesis of Spirocyclohexadienones by NHC‐Catalyzed Formal [3+3] Annulation Reaction of Enals
Author(s) -
Yetra Santhivardhana Reddy,
Mondal Santigopal,
Mukherjee Subrata,
Gonnade Rajesh G.,
Biju Akkattu T.
Publication year - 2016
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201507802
Subject(s) - enantioselective synthesis , stereocenter , annulation , chemistry , catalysis , carbene , cascade reaction , formal synthesis , organocatalysis , dehydrogenation , quaternary carbon , combinatorial chemistry , michael reaction , organic chemistry , stereochemistry
The enantioselective synthesis of pyrazolone‐fused spirocyclohexadienones was demonstrated by the reaction of α,β‐unsaturated aldehydes with α‐arylidene pyrazolinones under oxidative N‐heterocyclic carbene (NHC)catalysis. This atom‐economic and formal [3+3] annulation reaction proceeds through a vinylogous Michael addition/spiroannulation/dehydrogenation cascade to afford spirocyclic compounds with an all‐carbon quaternary stereocenter in moderate to good yields and excellent ee values. Key to the success of the reaction is the cooperative NHC‐catalyzed generation of chiral α,β‐unsaturated acyl azoliums from enals, and base‐mediated tandem generation of dienolate/enolate intermediates from pyrazolinones.