Photoreactions of 1-Acetylisatin with Alkynes:  Regioselectivity in Oxetene Formation and Easy Access to 3-Alkylideneoxindoles and Dispiro[oxindole[3,2‘]furan[3‘,3‘ ‘]oxindole]s

摘要: Photoinduced reactions of 1-acetylisatin (IS) with diphenylacetylenes 1a−c, 1-(p-methoxyphenyl)propyne 2, and 1,4-diphenyl-1,3-butadiyne 3 gave β,β-disubstituted 3-alkylidene oxindoles 6−12 respectively via [2+2] cycloaddition 3IS* the alkyne subsequent oxetene ring opening. Photoreactions IS phenylacetylenes 4a−d cyclopropylacetylene 5 furnished dispiroindole[3,2‘]furan[3‘,3‘ ‘]indoles 13 14. Compounds 14 are formed in tandem initiated by alkynes to give spirooxetenes Va Vb, which upon spontaneous opening α,β-unsaturated aldehydes IVa IVb. It is proposed that hydrogen abstraction from C(O)−H functionality IV followed dissociation triplet isatin ketyl (A)−aldehyde acyl (B) radical pair an oxygenphilic attack B at C3 carbonyl oxygen atom a neutral 2:1 (IS:4) C, took part intramolecular cyclization ...