Access to Dienophilic Ene-Triketone Synthons by Oxidation of Diketones with an Oxoammonium Salt

Abstract

Here we describe the oxidation of 1,3-cyclohexanediones with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (Bobbitt’s salt) to generate 5-ene-1,2,4-triones in moderate-to-good (40–80%) yields. This inexpensive oxidant facilitated an unprecedented cascade of oxidation and elimination to yield novel ene-triketones. The reactivity of these products was explored in the Diels-Alder reaction and provided moderate-to-good yields of cycloaddition products. The products described in this study represent unique, densely functionalized, and versatile building blocks for the synthesis of more complex molecules.

Dehydrogenation of Perfluoroalkyl Ket­ones by Using a Recyclable Oxoammonium Salt

“…We postulated that rather than proceeding in a concerted pathway, the reaction likely was a two‐step process. The first step involved precedented α‐alkylation of the intermediate enolate (or enol), whose formation is likely facilitated by lutidine 3,14. Once alkylated, the carbonyl undergoes rapid hydration by any trace amount of water in the system (i.e., from the salt or solvent) 13.…”

Organofluorine chemistry: Difluoromethylene motifs spaced 1,3 to each other imparts facial polarity to a cyclohexane ring

“…The dimethyl-diketone 5c was prepared by double methylation of 5b [25] (Scheme 2). Two different O -alkylated products 7 and 8 were also obtained as significant byproducts.…”

2,2,6,6-Tetramethylpiperidine-Based Oxoammonium Salts

“…Starting from 1,3-cyclohexanediones, ene-triketones can be obtained in 40-80% yield via the exhaustive oxidation with Bobbitt's salt. 7 The reactivity of these oxidized products was explored via Diels-Alder reactions. …”