phosphaalkenes (1 and 2) with 1,3 dienes such as methyl sorbate and 1-methoxy 3-trimethylsilyloxy-1,3 butadiene leads to functionalized λ3 phosphabenzenes 6, 9, 12, 13 and 16 after aromatization of the primary adducts. The aromatization may occur either spontaneously or after chemical transformations. The reversible cycloaddition has allowed the synthesis of isomeric phosphabenzenes 6 and 9. Diels-Alder