The addition of n-butyl nitrite to a 1:1 molar equivalent of 2-alkyl-1-indanone [R = CH3 (1b), C2H5 (1c), C3H7 (1d), iso-C3H7 (1e),n-C4H9 (1f), and t-C4H9 (1g)]-hydrochloric acid, and to a 2-phenyl- (1h)and 2-cyano-1-indanone (1k)-sodium alkoxide mixture, produced 2-hydroxy-3-alkyl- or -arylisocarbostyrils (3b-3h and 3k, respectively) in decreasing yields (69-14%). Reverse addition of acid to an indanone-nitrite mixture led to the isolation of the stable dimeric 2-alkyl-2-nitroso-1-indanones [2b-2g and 2i (R = Ac)] in decreasing yields (90-20%). Since 2b-2g were isomerized to 3b-3g, respectively, in both acid (92-96%) and base (90-96%), the nitrosation step (1 →2) clearly determines product yield in the conversion 1 →3. Reduction of 3b-3f and 3h with iodine and red phosphorus in glacial acetic acid led to the known 3-alkyl- or -arylisocarbostyrils (4b-4f and 4h). Both hydrochloric acid and methanolic sodium methoxide converted 2i to 2-oximino-l-indanone (2a), as did nitrosation of 1-indanone (1a). 2-Carboxy-1-indanone (1j) underwent nitrosative decarboxylation to 2a. Ring-opened intermediates in the isomeriction 2b → 3b are suggested by the conversion of o-carboxy- (19) and o-carbomethoxybenzyl methyl ketoxime (24) to 3b, in acid and base, respectively. 2,3,3-Trimethyl-1-indanone (1m), 2-methyl- (32a), and 2-ethyl-1-tetralone (32b) were converted to their respective nitroso dimers, 2m, 33a, and 33b. Acid treatment of 2m and base treatment of 33a and 33b led to ring-opened hydrolysis products, 3-methyl-3-(o-carboxyphenyl)-2-butanone oxime (29), 4-(o-carboxyphenyl)-2-butanone (34a), and 1-(o-carboxyphenyl)-3-pentanone (34b), respectively. A similarity of ultraviolet spectra, the presence of a C-4 vinyl proton signal in the nmr of 3b, 4b, and 2,3-dimethylisocarbostyril (35), and the lack of N→O absorption in 3b, is consistent with the existence of 2-hydroxy-3-methylisocarbostyril and 3-methylisocarbostyril predominantly in their respective lactam forms, 3b and 4b. Infrared, ultraviolet, and nmr data are reported for compounds in the series 1-4, inclusive. © 1966, American Chemical Society. All rights reserved.