New synthetic reactions of enamine phosphonates

Abstract

We tried the preparation of α-chloro-α,β-unsaturated ketones by the use of benzenesulfonyl chloride as a chlorenium source. But unexpectedly α-chloro-β-benzenesulfonyl ketones were obtained. This unexpected products were the result of 1,4-addition of lithium benzenesulfinate or benzenesulfinic acid to α-chloro-α,β-unsaturated imine intermediates. The synthesis of α,β-unsaturated imines was carried out in one-pot procedure, which was based upon that the nucleophilic addition of lithiated methylphosphonate to nitriles and subsequent Horner-Emmons reaction. The treatment of this α,β-unsaturated imine with an excess of reducing agent led to corresponding primary E-allylic amines in good yields. We carried out reduction of the enamine intermediates, which could be obtained from reaction of lithiated methylphosphonate and nitriles. Some β-aminophosphonate were obtained. While attempting to synthesize β-aminophosphonates from enamine phosphonates by selective reduction of enamine group using $LiAlH_4$, we unexpectedly obtained the cleanly dephosphorylated ketones. Lithiated β-ketophosphonate also could be converted to dephosphorylated ketones by treatment of $LiAlH_4$. We studied the mechanism of this unexpected dephosphorylation of enamine phosphonates and β-ketophosphonates. The convenient preparations of vinyl selenides and ketene selenoacetals were studied. Reaction of the lithio anions derived from diethyl alkylphosphonates with phenylselenenyl bromide gave the diethyl phenylselenoalkylphosphonate anions. In situ reaction with aldehydes or ketones gave vinyl selenides in a convenient one- pot procedure. Diethyl 1,1- bis(phenylseleno)methylphosphonate was prepared from diethyl methylphosphonate and phenylselenenyl bromide. And its reactions with aldehydes and ketones were investigated. The products obtained from reaction with aldehydes were ketene selenoacetals. With ketones the reaction took an unexpected route and the major products were the α- phenylsel...