Switching between P-acylation and O-acylation of H -phosphonates with chloroformates by changing acyl pyridinium and acyl ammonium ions in a microflow reactor.

We report the first switchable acylation of H -phosphonate with chloroformate. The acylation site (P vs. O) in H -phosphonate was switched by changing the acyl pyridinium/ammonium ions. Unexpected phosphite formation was observed during the O-acylation of H -phosphonate. Twenty-six structurally diverse phosphotriesters and phosphonoformate esters were synthesized in microflow reactors.