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

Comprehensive Summary 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.