Spaltung der Ylid-Bindung in Phosphor-Yliden: Photolyse von thiophosphoranylsubstituierten (Triphenylphosphoranyliden)methanen / Cleavage of Ylidic Bonds in Phosphorus Ylides: Photolysis of Thiophosphoranyl-Substituted (Triphenylphosphoranylidene)methanes

Abstract

The thiophosphoranyl-substituted (triphenylphosphoranylidene)methanes 1, 6a, b are cleaved photolytically (λ > 300 nm, 3 d, 0 °C) to yield triphenylphosphane and the thio-aza-phosphetanes 3 and 8 a, b, b′, respectively. The formation of these heterocycles is explained invoking insertion of the carbenes 2 and 7 a, b into the methine CH bond of one of the isopropyl groups. If 6a is irradiated for 16 h in the presence of the phosphanes P(NMe2)3, P(OMe)3 or P(nBu)3, the new ylides 9 a, b, c are obtained along with small quantities of 8 a. These results indicate a cleavage of the ylidic bond in 1 and 6 a, b. The failure of attempted cyclopropanation reactions of olefins as well as the absence of the expected product of a 1,2-H shift, 10, in the case of the photolysis of 6b leave doubts as to the occurrence of free carbenes.