Cycloaddition of the diene 3, 4-dihydro-7-methoxy-l-vinylphenanthrene and CH3PC12 proceeded in good yield to give, after hydrolysis, a derivative with the tetracyclic steroid system containing phosphorus at the 17 position (A). The isomeric 2-vinyl compound also gave a tetracyclic derivative (a 15-phosphasteroid. B), but less readily. Hy-