Electrochemical Reduction of Cyclohex‐2‐enones

Abstract

SummaryThe electrochemical reduction of the cyclohex-Zenones 1 a-1 e (mercury cathode, CH&N, BudNBF4) was studied by means of cyclic voltammetry, d. c. polarography, coulometry and chemical product analysis. Compounds 1 a-1 c give a mixture of the hydrodimers 4 and 5 via formation of the radical anion 2 by an irreversible one electron transfer, followed by protonation and dimerization of the allylic radical 3. The 6-halocyclohex-2-enones 1 d and 1 e exhibit two distinct reduction waves. The first corresponds to an irreversible two electron transfer with formation of the halide anion and the enolate anion 6 which gives 1 b by protonation. The second wave corresponds to a quasi-reversible one electron transfer to 6 to afford the radical dianion 7 (Scheme 2).The electrochemical reduction of a, p-unsaturated ketones in general [l] [2] and of cyclohex-2-enones in particular [3-51 has been investigated by several research groups. Although the mechanism for this reaction in aqueous systems seems to be well understood [6] [7], less is known about it in nonaqueous media.We now report results on a comparative study of the electrochemical reduction of the cyclohex-2-enones 1 a-1 e (Scheme I ) in acetonitrile by cyclic voltammetry, d. c. polarography, coulometry and chemical analysis. In order to correlate reliably the experimental data of the controlled potential electrolyses for identification of the reaction products with those of the mechanistic studies, all experiments were run under as similar conditions as possible. This implies that the conditions were far from being optimal for preparative electrolyses as reflected in the modest yields of isolated products.Scheme I

Photocycloaddition of Cyclohex‐2‐enones to Tetramethoxyethylene: Formation of 2,2,3,3‐Tetramethoxy‐1‐oxaspiro[3.5]non‐5‐enes

“…In V us. Ag/Ag+ [13]. In eV, taken or estimated from 1141. product ratio 314 and the overall yield are strongly influenced.…”

Photoreduction of Cyclic α‐Fluoroketones

“…The electrochemical reduction of a-haloketones on Hg affords the parent carbonyl compound [16] [17]. The overall reaction involves cleavage of the C-halogen bond in a two-electron sequence to give the enolate and the halide anion.…”

Electrochemical investigations on β-chlorovinylaldehydes in aprotic media

“…The electrochemical behaviour of carbonyl compounds has been studied almost as extensively as that of nitro compounds. But, the electrochemical reduction of a, flunsaturated aldehydes and ketones in protic (Zuman and Michl 1961;Zuman 1967;Ryvolova-Kejharova and Zuman 1969;Barnes 1969, 1971;Spritzer and Zuman 1981;Vadaszy and Cover 1974; Mandell e t a l 1971,1976) and aprotic (Wawzonek and Gundersen 1964;Margaretha and Tissot 1977;Mellor et ai 1981;Powell and Wightman 1987) media has been found to be more complex than that of saturated carbonyl compounds. Recently, we have noticed that the reduction of various fl-chlorovinylaldehydes in buffered aqueous ethanolic solutions at a mercury cathode yielded electrohydrodimerized products in major amounts (Saiganesh et al 1989).…”