title: Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and N,O-Acetal Derivatives.
abstract: Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective γ-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective γ-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronucleophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective γ-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched α,α-disubstituted α-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and γ-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nucleophilic oxazolide and the electrophilic phosphonium intermediate.
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Tianli
authors.initials: T
authors.lastname: Wang
authors.affiliation: School of Chemistry and Chemical Engineering, Chongqing University , Chongqing 400030, P. R. China.
authors.forename: Zhaoyuan
authors.initials: Z
authors.lastname: Yu
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Ding Long
authors.initials: DL
authors.lastname: Hoon
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Claire Yan
authors.initials: CY
authors.lastname: Phee
authors.affiliation: School of Chemistry and Chemical Engineering, Chongqing University , Chongqing 400030, P. R. China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Lan
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.|National University of Singapore (Suzhou) Research Institute , 377 Lin Quan Street, Suzhou Industrial Park, Suzhou, Jiangsu P. R. China , 215123.
authors.forename: Yixin
authors.initials: Y
authors.lastname: Lu
mesh_terms: D000080:Acetals / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry*; D002384:Catalysis; D010080:Oxazoles / Q000737:chemistry*; D010720:Phosphines / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000080:Acetals; D000596:Amino Acids; D010080:Oxazoles; D010720:Phosphines