Phospha‐michael reactions involving p‐heterocyclic nucleophiles

P‐heterocyclic γ‐ketophosphonates were synthesized by the Michael reaction of methyl vinyl ketone with dibenzo‐1,2‐oxaphosphorine 2‐oxide, 1,3,2‐dioxaphosphorine 2‐oxide and benzo‐1,3,2‐dioxaphospholane 2‐oxide, respectively. In the first two cases, 50% of 1,8‐diazabicyclo[5.4.0[undec‐7‐ene had to be used that was also required in the addition of dibenzooxaphosphorine oxide to cyclohexenone to result in the formation of the corresponding γ‐ketophosphonate. The addition of dibenzooxaphosphorine oxide to less reactive 1,2‐dihydrophosphinine oxide was accomplished after activation by an equimolar amount of trimethylaluminum to afford a 3‐P(O)<‐1,2,3,6‐tetrahydrophosphinine oxide, which was subjected to catalytic hydrogenation to provide the corresponding 1,2,3,4,5,6‐hexahydrophosphinine oxide.