One-pot bifunctionalization of unactivated alkenes, P(O)-H compounds, and N-methoxypyridinium salts for the construction of -pyridyl alkylphosphonates

Abstract

beta-Pyridylphosphines consisting of vicinal pyridine and phosphine groups possess soft acceptor properties of phosphines and hard sigma-donor features of pyridines. An efficient method for the synthesis of -pyridyl alkylphosphonates was developed via a three-component reaction between P(O)-H compounds, alkenes and N-methoxypyridinium salts under mild conditions. The reaction is thought to occur by the addition of a phosphonyl radical to the alkene to form alkyl radical intermediate, which goes on to add to the N- N-methoxypyridinium salt. Solvation plays an important role and DFT calculations suggest that the solvation effect is critical in the first step where an alkyl radical intermediate is formed by coupling the phosphonyl radical and the alkene substrate. A plausible mechanism is proposed based on DFT calculations and this novel methodology is applied to a variety of heteroarenium salts and alkene substrates to prepare various synthetically and biologically important -pyridyl alkylphosphonates.