title: Tandem diastereo- and enantioselective preparation of aryl and alkyl cyclopropyl carbinols with three adjacent stereocenters using perhydrobenzoxazines and diethylzinc.
abstract: The enantio- and diastereoselective one-pot ethylation/cyclopropanation is efficiently promoted by a chiral perhydrobenzoxazine. The catalytic system tolerates a wide range of di- and trisubstituted α,β-unsaturated aldehydes and has been found to be highly diastereo- and enantioselective. Enals leading to intermediates lacking allylic strain or with either A(1,2) or A(1,3) strain afford the corresponding syn hydroxycyclopropanes very selectively. While α-methyl enals are successfully ethylated/cyclopropanated, the presence of bulky substituents at the alpha position of the enal constitutes a limitation to the substrate scope. The use of 1,1-diiodoethane allows the obtention of the corresponding enantioenriched cyclopropylcarbinol, which bears carbon-substituents at all three positions of the ring, with good enantiocontrol, although moderate diastereoselectivity. A procedure for the asymmetric one-pot arylation/cyclopropanation of enals is proposed, which involves the use of triarylboroxin, diethylzinc and diiodomethane.
authors.affiliation: Instituto CINQUIMA and Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Valladolid, Paseo de Belén, 7, 47011 Valladolid, Spain. javiernr@qo.uva.es.
authors.forename: Rebeca
authors.initials: R
authors.lastname: Infante
authors.forename: Javier
authors.initials: J
authors.lastname: Nieto
authors.forename: Celia
authors.initials: C
authors.lastname: Andrés
mesh_terms: D048588:Benzoxazines / Q000737:chemistry*; D003521:Cyclopropanes / Q000138:chemical synthesis* / Q000737:chemistry; D000432:Methanol / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D048588:Benzoxazines; D003521:Cyclopropanes; D009942:Organometallic Compounds; C454811:diethylzinc; D000432:Methanol