Preparative and mechanistic studies toward the rational development of catalytic, enantioselective selenoetherification reactions.
A systematic investigation into the Lewis base catalyzed, asymmetric, intramolecular selenoetherification of olefins is described. A critical challenge for the development of this process was the identification and suppression of racemization pathways available to arylseleniranium ion intermediates. This report details a thorough study of the influences of the steric and electronic modulation of the arylselenenyl group on the configurational stability of enantioenriched seleniranium ions. These studies show that the 2-nitrophenyl group attached to the selenium atom significantly attenuates the racemization of seleniranium ions. A variety of achiral Lewis bases catalyze the intramolecular selenoetherification of alkenes using N-(2-nitrophenylselenenyl)succinimide as the electrophile along with a Brønsted acid. Preliminary mechanistic studies suggest the intermediacy of ionic Lewis base-selenium(II) adducts. Most importantly, a broad survey of chiral Lewis bases revealed that 1,1'-binaphthalene-2,2'-diamine (BINAM)-derived thiophosphoramides catalyze the cyclization of unsaturated alcohols in the presence of N-(2-nitrophenylselenenyl)succinimide and methanesulfonic acid. A variety of cyclic seleno ethers were produced in good chemical yields and in moderate to good enantioselectivities, which constitutes the first catalytic, enantioselective selenofunctionalization of unactivated olefins.
Denmark
Scott E
SE
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States. sdenmark@illinois.edu
Kalyani
Dipannita
D
Collins
William R
WR
D002384:Catalysis; D004987:Ethers / Q000737:chemistry*; D015394:Molecular Structure; D012643:Selenium / Q000737:chemistry*; D013237:Stereoisomerism
D004987:Ethers; D012643:Selenium