Enantioselective Synthesis of Spirocyclohexadienones by NHC-Catalyzed Formal [3+3] Annulation Reaction of Enals.
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.
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-411008 (India) http://academic.ncl.res.in/at.biju.
Santhivardhana Reddy
SR
Yetra
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-411008 (India) http://academic.ncl.res.in/at.biju.
Santigopal
S
Mondal
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-411008 (India) http://academic.ncl.res.in/at.biju.
Subrata
S
Mukherjee
Centre for Materials Characterization, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-411008 (India).
Rajesh G
RG
Gonnade
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-411008 (India) http://academic.ncl.res.in/at.biju. at.biju@ncl.res.in.
Akkattu T
AT
Biju
N-heterocyclic carbenes; annulation reactions; asymmetric catalysis; organocatalysis; spiro compounds