Study on the synthetic reactions of β-activated phosphonates

Abstract

A convenient synthetic methods for the preparation of a variety of $\beta$ -keto phosphonate derivatives, enamine phosphonates, and 1,2-epoxyalkane phosphonates were studied. Various $\alpha$ -alkyl or $\alpha$ -hetero atom substituted $\beta$ -keto and enamine phosphonates are obtained by the nucleophilic addition of $\alpha$ -lithioalkane phosphonates to nitriles as an acyl cation equivalent, followed by treatment with electrophiles and hydrolysis or ketimine enamine isomerization. 1,2-Epoxyalkane phosphonates are prepared by the combination of chlorination of diethylalkane phosphonates and intramolecular substitution reaction in the presence of 2eq. HMPT. In this reaction benzenesulfonyl chloride is used as a chlorenium source. It is also studied the reactions to obtain $\alpha$, $\beta$ -unsaturated ketones, deoxybenzoin derivatives,$\beta$ -keto sulfides, and 1,1-dichloro olefins. The preparation of $\alpha$, $\beta$ -unsaturated ketones is carried out through the nucleophilic addition of $\alpha$ -lithiomethane phosphonate to nitriles and subsequent witting-Horner reaction without isolation of $\beta$ -keto phosphonates. The deoxybenzoin and $\beta$ -keto sulfide derivatives are prepared by the nucleophilic addition of $\alpha$ -lithioanion of the phosphonates bearing an electron stabilizing group to aromatic nitriles and subsequent treatment with 5N-NaOH solution, and two possible mechanisms are proposed. A variety of 1,1-dichloro olefins are prepared by combination of the dichlorination and Wittig-Horner condensation starting from diethyl methylphosphonate and benzenesulfonyl chloride in the presence of 3eq. of n-BuLi in THF. The present method is useful both aldehydes and ketones and no reaction occurred with use of LDA as a base.