ORGANOSELENIUM CHEMISTRY A STUDY OF INTERMEDIATES IN THE FRAGMENTATION OF ALIPHATIC KETOSELENOXIDES. CHARACTERIZATION OF SELENOXIDES, SELENENAMIDES AND SELENOLSELENINATES BY (1)H-, (13)C- AND (77)Se-NMR

Article abstract of DOI:10.1016/S0040-4020(01)96716-X

A series of β-ketoselenenic acids was generated at low temperature (-20 deg C to -50 deg C) 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 deg C was characterized by NMR spectroscopy ( (1)H, (13)C, (77)Se ) 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(CH2Ph)2 (R=PhC(O)C(CH3)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 monooxide, 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 deg C.The latter gave what appeared to be a selenolseleninate (40) which again disproportionated at -17 deg C.