Retrodienic reactions. Part 2. Vinyl- and propenyl-phosphines: synthesis by flash vacuum thermolysis and characterization

Abstract

The primary unsaturated phosphines, vinylphosphine (1), isopropenylphosphine (2) and (E)-prop-1-enylphosphine (3) have been synthesized by flash vacuum thermolysis of their formal Diels–Alder adducts with anthracene, cyclopentadiene, or 1,3-diphenylisobenzofuran, obtained by cycloaddition of these dienes with the corresponding dialkyl alkenylphosphonates, followed by reduction with lithium aluminium hydride–chlorotrimethylsilane. Compounds (1)–(3) were characterized from their spectral data and also as tungsten complex derivatives. The phosphines (1)–(3) exhibit a remarkable and unexpected stability [t_½ca. 8 days for (1) and 5 days for (2) and (3)] under neutral conditions, in the dark, at room temperature, and were also observed by direct reduction of the corresponding phosphonates in tetrahydrofuran solution.