Organocatalytic, Enantioselective Synthesis of Cyclohexadienone Containing Hindered Spirocyclic Ethers through an Oxidative Dearomatization/Oxa-Michael Addition Sequence.
An unprecedented enantioselective oxa-Michael reaction of α-tertiary alcohols using cinchona-alkaloid-based chiral bifunctional squaramide catalysts is reported. An oxidative dearomatization of phenol followed by an enantioselective oxa-Michael addition sequence provided a broad array of chiral sterically hindered tetrahydrofurans and tetrahydropyrans attached to a cyclohexadienone moiety in spiro fashion. In general, good yields and excellent enantioselectivities (up to 99 %) were observed. The chiral oxo-cycles obtained have easily been transformed into chromans without disturbing the enantioselectivity.
Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, Bhopal By-pass Road, Bhauri, Bhopal-, 462066, India.
Reddy Rajasekhar
RR
Reddy
Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, Bhopal By-pass Road, Bhauri, Bhopal-, 462066, India.
Satish Sonbarao
SS
Gudup
Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, Bhopal By-pass Road, Bhauri, Bhopal-, 462066, India.
Prasanta
P
Ghorai
asymmetric synthesis; chromans; organocatalysis; oxa-Michael addition; tetrahydrofurans