α-Diones from Cyclic Oxamides and Organolithium Reagents: A New, General and Environmentally Beneficial Synthetic Method

Although the reaction of organolithium compounds with tetraalkyl oxamides does not lead to α-diones, their cyclic analog, 1,4-dimethylpiperazine-2,3-dione, reacts with RLi or RMgBr to produce α-diones in excellent yields. The 1,4-dialkylpiperazine-2, 3-dione reagent can be obtained in high yield from diethyl oxalate and the N,N′-dimethylethylenediamine. Although this synthesis is broadly applicable, it is limited to symmetrical α-diones. Unsymmetrically substituted α-diones can be obtained when two different RLi species are sequentially added to long-chain 1,4-dialkylpiperazine-2,3-diones. An economically and ecologically important aspect it that, at the end of the α-diketone synthesis, the N,N′-dialkylethylenediamines can easily be recovered and recycled to their respective piperazinediones. The net reaction therefore constitutes a synthesis of α-diones from diethyl oxalate and an organometallic reagent. The environmental problems associated with the oxidation of acyloins or other α-dione precursors by transition metal oxides are avoided. Contents: Introduction: Ferrocenil and Other Things α-Dione Syntheses The Oxamides A Mechanism? A First Attempt: The Synthesis of Benzil Generalizations Monolithio Ferrocene and Diferrocenyl Ethanedione Modifications: More Soluble DMPD Derivatives Intermezzo: Piperidine to the Rescue? Synthesis of Didecyl Piperazinedione and of its Dibenzyl Analog The Net Result The Moral of the Story