1- Acylindoles, photoisomerization

Photoisomerization of 1-acylindoles yields 3-acylindolenines, as exemplified by the conversion of compound (28) into compound (29) (81JA6990). 

Ban s general entry to the Strychnos and Aspidospema alkaloids makes ingenious use of a novel photoisomerization of 1-acylindole derivatives to 3-acylindolenines. When applied to the tryptamine derivative (132), the derived indolenine (133) spontaneously rearranged, with formation of the indole-amide (134) in 80% yield (Scheme 22). Obvious stages then led to (135), which... 

Isoxazole-oxazole photoisomerization was studied by irradiation of matrix-isolated 3,5-dimethylisoxazole (18) at 222 nm. 2-Acetyl-3-methyl-2H-azirine (20) was obtained, likely through an acetyl vinyl nitrene intermediate 19 as primary photoproduct, while upon longer time UV irradiation, two additional photoproducts were identified as acetyl nitrile ylide 21 and 2,5-dimethyloxazole (22) (13JOC10657). Analogously, 3,5-diphenylisoxazole and 2-benzoyl-3-phenyl-2f/-azirine behaved as precursors to triplet vinyl nitrene (of type 19) through laser flash photolysis (13JOC11349). Reductive heterocycle—heterocycle transformations of (2-nitrophenyl)isoxazole precursors, such as 23 and 26, afforded 4-amino quinolines of type 24, quinolin-4(lfJ)-ones 25, and 3-acylindoles 27. Che-moselective heterocyclizations were observed from 3,4-,4,5-, and 3,4-bis(2-nitrophenyl)isoxazoles (13OL2062). 

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