Alkylation and dephosphonylation of β-keto phosphonate

Abstract

The alkylation of cyclic and acyclic β-keto phosphonates was developed. The reaction with reactive halides in tetrahydrofuran at room temperature afforded roughly good yields of the alkylated products in a few hours. Sodium hydride was employed as a base. And, it was found that the alkylated β-keto phosphonates involving no α-hydrogen but γ-hydrogen are dephosphonylated by reaction of the lithium enolates with LAH. The yields of dephosphonylations were good or moderate and reaction times were within an hour. Not only normal butyllithium but LDA was employed as a base for some β-keto phosphonates. LDA gave somewhat better results. The mechanism has not been elucidated yet although various attempts were made. In conclusion, the alkylation and the dephosphonylation of β-keto phosphonate can be utilized in the preparation of a variety of α-substituted ketones.