Dynamic Kinetic Resolution of Alkenyl Cyanohydrins Derived from α,β-Unsaturated Aldehydes: Stereoselective Synthesis of <i>E</i>-Tetrasubstituted Olefins
作者:Jadab Majhi、Ben W. H. Turnbull、Ho Ryu、Jiyong Park、Mu-Hyun Baik、P. Andrew Evans
DOI:10.1021/jacs.9b04384
日期:2019.7.31
A novel dynamic kinetic resolution (DKR) of tetrasubstituted alkenyl cyanohydrins prepared from the corresponding α,β-unsaturatedaldehydes is described. The deprotonation of a geometrical mixture of tetrasubstituted alkenyl cyanohydrins with sodium diisopropylamide (NaDA) enables the equilibration of the E- and Z-olefins and the selec-tive functionalization of former to selectively afford the E-adduct
Type II photoreactions of α-alkyl β-oxoesters. Neighboring group effect on 1,4-biradical reactions and effective internal filter effect by the type II photoproduct
The α-alkyl β-oxoesters 1 undergo typeIIphotoreactions. The process of back hydrogen transfer in the 1,4-biradical intermediate to revert to the starting ester is suppressed because of the intramolecular hydrogen bonding between the hydroxyl and carboalkoxyl groups in the biradical intermediate. The hydrogen bonding determines the stereochemistry of 1,4-biradical cyclization. The cyclobutanols having
The δ- and β-oxoester 1 and 5 underwent the TypeIIphotoreaction to give the stereoisomeric cyclobutanol 2 and 6, respectively; the ethoxycarbonyl group in the esters determines the stereochemistry of 1,4-biradical cyclization.