Diels‐Alder reaction of (2,4,6‐trialkylphenyl)phospholes with N‐phenylmaleimide

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 delocalisation, underwent the Diels‐Alder reaction with N‐phenylmaleimide to give predominantly cycloadducts 4a–c with the trialkylphenyl substituents anti to the phosphanorbornene double bond. With increasing aromaticity, the cycloaddition was slower. The stereostructure of the products ( 6 and 7 ) obtained after oxidation was confirmed by stereospecific ²J_PC NMR couplings and by an independent synthesis. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:271–275, 2000