Kinetic resolution of 5-substituted cycloalkenones by peptidic amidophosphane-copper-catalyzed asymmetric conjugate addition of dialkylzinc

Abstract

Asymmetric conjugate alkylation reaction of racemic 5-substituted cyclohexenones with dialkylzinc reagents was catalyzed by 2–5 mol % of dipeptidic amidophosphane-Cu(MeCN) 4BF 4 in toluene at 0 °C for 20 min to recover enantioenriched starting 5-substituted cyclohexenones with 88–98% ee in 28–41% yield along with trans major 3-alkylated 5-substituted cyclohexanones with 81–90% ee in 53–60% yield. Complete consumption of starting racemic 5-TMS-cyclohexenone by treating with diethylzinc under the catalytic asymmetric reaction conditions gave trans major 85:15 mixture of trans- and cis-3-ethyl-5-TMS-cyclohexanones with 15% ee (for trans) in 83% combined yield, indicating that the conformation-controlled trans-alkylation of cyclohexenone prevails over chiral catalyst-controlled enantiofacial differentiation.