Diastereoselective [Cu(MeCN)4BF4/BF3·Et2O]-Catalyzed Cyclopropenation of Alkynes: Asymmetric Synthesis of β-Amino-α-cyclopropenyl Phosphonates

Abstract

The diastereospecific formation of β-amino-α-cyclopropenyl phosphonates has been achieved in moderate yields from the cyclopropenation of 1-alkynes with dialkyl α-diazophosphonates. The reaction was performed by using a combined catalyst consisting of Cu(MeCN)4BF4 and BF3·Et2O as additive in dichloromethane at 40 °C. A possible mechanism for the reaction has been proposed to explain the origin of the activation and the asymmetric induction. This method provides a versatile approach to β-amino-α-cyclopropenylphosphonates containing a quaternary stereogenic center with good efficiency and diastereoselectivity.