A series of β-ketoselenenic acids was generated at low temperature ( - 20° to - 50°) by selenoxide
syn elimination of appropriate selenoxides (
13-ox,
16-ox,
35-ox,
38-ox, and
39-ox). No evidence for the buildup of significant concentrations of selenenic acid was obtained. A selenolseleninate (
15, 2,2' - diseleno - bis(1 - phenyl - 2 - methyl -1 - propanone) - Se - oxide) was detected as an intermediate in the decomposition of
13-ox and
16-ox. This compound, which is stable in solution below - 50° was charaeterized by NMR spectroscopy (
1H,
13C,
77Se) and by its thermal decomposition and reactions with phosphite (reduction to diselenide
6) and dialkylamines (formation of selenenamide
11). Decomposition of
15 in the presence of dibenzylamine resulted in trapping of a selenenic acid-like species (RSeSeOH) to give RSeSeN(CH
2Ph)
2 (R = PhC(O)C(CH
3)
2). Although
15 could not be prepared by oxidation of diselenide 6, it was possible to prepare a cyclic selenolseleninate (4,4-dimethyl-1,2-diselenolane monoxide,
20) by oxidation of the related diselenide (
19). Attempts to prepare more stable aliphatic selenenic acids by blocking the principal decomposition pathway of
15 were not successful. Thus 1 - benzoyl -1 - cyclopropaneselenenic acid was generated from
35-ox and
38-ox and 1 - benzoyl - 2,2 - dimethylcyclopropaneselenenic from
39-ox. The former underwent normal disproportionation (to
36 and
37) even when prepared at -49°. The latter gave what appeared to be a selenolseleninate (
40) which again disproportionated at -17°.
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