Oxidation of 1H-2-Benzoselenopyrans. Generation of Benzoselenophenes, Benzaldehydes, and Benzophenones
摘要:
Oxidation of 1H-2-benzoselenopyrans bearing electron-withdrawing substituents gave benzoselenophenes, benzaldehydes, and benzophenone derivatives via the corresponding selenoxides followed by Pummerer and [3,3]sigmatropic rearrangements.
Selenobenzophenone reacts as a diene with dimethylacetylenedicarboxylate (DMAD) to lead to dimethyl 1H-1-diphenylmethyl-1-phenyl-2-benzoselenopyran-3,4-dicarboxylate (5c) in moderate yield; the initial [4 + 2] cycloaddition is followed by the addition of another 1 mol equiv of selenobenzophenone. The reaction might proceed through carbene insertion of the primary cycloadduct. On the other hand, 4