Diels-Alder Reactions of Trichlorophosphaethene

Article abstract of DOI:10.1021/jo00128a015

The Diels-Alder reactions of trichlorophosphaethene (3), generated in situ from dichloro(dichloromethyl)phosphine (2), with 1-vinylnaphthalene (6), 1-(1-methylethenyl)cyclohexene (4), and 1-<1-(trimethylsiloxy)ethenyl>cyclohexene (13) at 60-75 deg C, are described.The reactions of 3 with 4 and 6 afforded, after aromatization of the primary Diels-Alder adducts 5 and 8 under the influence of triethylamine, the 2-chlorophosphinines 9 and 11, respectively.The reaction with 13, however, led to the formation of the "double adduct" 16, which could not be isolated in pure form.The formation of the "double adduct" is explained by a subsequent Diels-Alder reaction of 13 with dihydrophosphinine 15, which is formed after HCl elimination from the primary Diels-Alder adduct 14.The reaction of 13 with 23, the pentacarbonyltungsten complex of 2, furnished 27, the pentacarbonyltungsten complex of 16, which was isolated in pure form.The regiochemistry of the Diels-Alder reactions described above is discussed on the basis of MNDO/PM3 calculations of the frontier molecular orbital coefficients.The Diels-Alder reactions proceed with normal electron demand, and the experimentally observed regiochemistry is in accordance with theoretical predictions.The formation of the "double adducts" 16 and 27 is rationalized as a consequence of the high HOMO energy of 13 compared with that of 4.