Reactivity of Germa- and Stannaphosphenes with o-Quinones and .alpha.-Diketones

Abstract

Stable germaphosphene 1 (germylidenephosphine) and stannaphosphene 2 (stannylidenephosphine) react with o-quinones (tetrachloro-o-benzoquinone, 3,5-di-tert-butyl-o-benzoquinone, and 1,2-naphthoquinone) to afford six-membered-ring heterocycles 3-8. Depending on the steric hindrance, one (from germaphosphene) or two (from stannaphosphene) regioisomers are formed. The structure of regioisomer 5a is unambiguously proved by an X-ray study; 5a crystallizes in the triclinic space group P ($) over bar 1 with Z = 2. Lattice constants were a = 10.102(1) Angstrom, b = 13.619(1) Angstrom, c = 18.820(2) Angstrom, alpha = 106.57(1)degrees, beta = 102.58(1)degrees, and gamma = 97.47(1)degrees. The main feature is the folding of the six-membered ring GePO(1)C(1)C(2)O(2) along the O(1)O(2) direction with an angle of 55 degrees between the two planes O(1)PGeO(2) and O(1)C(1)C(2)O(2). 1 and 2 undergo [2 + 4] cycloaddition with an a-diketone such as benzil, whereas an ene reaction is observed with biacetyl, leading to germylphosphine 11.