Irradiation of cyclic enones 5-8 in the presence of Me 3 SiOP(OMe) 2 or Me 3 SiOP(OEt) 2 gives phosphonosilylation products of 1,4-conjugate addition which are hydrolyzed to the phosphonoketones 11-14 in 82-92% isolated yields. An SET process in which the triplet enone accepts an electron from the silyl phosphite is proposed to be the key initiation step in these reactions.