A Tandem Route toward Isoxazolidine Fused Phospholene Skeleton Involving Dearomative [3+2] Cycloaddition of P-Heteroarenes and Nitrones

The demands for effective assembly of structurally complex molecular scaffolds from simple starting materials are continuously growing along with the development of organic chemistry. We have developed a tandem approach that assembles simple β-chloroethylphosphane, alkynyl imines (or alkynyl ketones), and nitrones into structurally complex isoxazolidine fused phospholene scaffolds through a sequential process involving phospha-Michael addition, intramolecular cyclization, and dearomatizing [3+2] cycloaddition reactions. The isoxazolidine-fused phospholene has three heteroatoms, including a junction phosphorus atom. After removing the coordinated tungsten group, these compounds can serve as potential P-stereogenic ligands and may have biological activities. Contrary to pyrroles and furans, the aromatic 2-phosphapyrroles and 2-phosphafurans are good 2π-electron candidates in the dearomative [3+2] cycloaddition reactions due to the poor overlap of the 2p-3p orbitals of the C=P moiety.