Diels-Alder reaction of (2,4,6-trialkylphenyl)phospholes with N-phenyl-maleimide.

2,4,6-Trialkylphenylphospholes 3a (R=Me), 3b (R=i-Pr) and 3c (R=t-Bu) with increasing flattening at phosphorus and hence with increasing electron delo calisation, underwent the Diels-Alder reaction with N-phenylmaleimide to gi ve predominantly cycloadducts 4a-c with the trialkylphenyl substi-tuents an ti to the phosphanorbornene double bond. With increasing aromaticity, the c ycloaddition was slower. The stereostructure of the products (6 and 7) obta ined after oxidation was confirmed by stereospecific (2)J(PC) NMR couplings and by an independent synthesis.