Rhenium-Catalyzed Synthesis of 2H-1,2-Oxaphosphorin 2-Oxides via the Regio- and Stereoselective Addition Reaction of β-Keto Phosphonates with Alkynes

Treatment of β-keto phosphonates (Horner-Wadsworth-Emmons reagents) with terminal alkynes in the presence of a rhenium catalyst gave 2H-1,2-oxaphosphorin 2-oxides with various substitution patterns. The reaction proceeds via two consecutive processes: cleavage of a carbon-carbon σ-bond of the β-keto phosphonate with insertion of the alkyne in a regio- and stereoselective manner, followed by cyclization of the resulting δ-phosphonyl α,β-unsaturated ketone yielding the 2H-1,2-oxaphosphorin 2-oxide. Horner-Wadsworth-Emmons reagents were found to add to nonpolar unsaturated compounds under neutral conditions.