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.
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States. sdenmark@illinois.edu
Scott E
SE
Denmark
Dipannita
D
Kalyani
William R
WR
Collins
D002384:Catalysis; D004987:Ethers / Q000737:chemistry*; D015394:Molecular Structure; D012643:Selenium / Q000737:chemistry*; D013237:Stereoisomerism
D004987:Ethers; D012643:Selenium