2- -one rearrangement

Photochemical cyclohex-2-enoneH> bicyclo (3.1.0) hexan-2-one rearrangement irradiation of testosterone acetate, 322 Photochemical rearrangements of cross-conjugated cyclohexadienones and their photoisomers... 

Photochemical cyclohex-2-enone bicyclo (3.1.0)hexan-2-one rearrangement, 320 Photochemical a-cyclopropyl ketone isomerization, 313... 

Tricyclo[3.3.1.03 6]non-7-en-2-ones (43, X = CH2), tricyclo[4.3.1.03-7]dec-8-en-2-ones (43, X = CH2CH2), and tricyclo[5.3.1.03,8]undec-9-en-2-ones (43, X = CH2CH2CH2) and other 3,8-bridged bicyclo[2.2.2]octen-2-ones rearrange in good to excellent yields to 4,6-bridged tricyclo[3.3.0,02,8]octan-3-ones (44) upon irradiation in acetone in the presence of acetophenone.149,170... 

An effective synthesis strategy via the novel quinoxalin-2(l//)-one/benzimidazol-2-one rearrangement that makes possible a rapid access to the N-pyrrolylbenzimidazol-2-ones from the readily available 3-aroylquinoxalin-2(l/7)-ones with various substituents and commercially available enamines (melhyl and ethyl 3-aminocrotonates) have been developed. The methodology was found to be general and... 

Attack on the electrophilic C-2 may occur as in the 2-aminothiazoles series, which probably explains the rearrangements observed in acidic medium (121, 711, 712, 723, 724), in aqueous medium with NaOAc (725), or with aqueous NaHCOj (725) (Scheme 232). That the initial attack probably involves the C-2 atom is substantiated by the fact that this rearrangement occurs under extremely mild conditions for 2-iinino-3-substituted-5-nitro-4-thiazolines (725). As the whole mechanism proposed (see p. 92) is reversible, when imino derivatives are submitted to such rearrangement conditions the rearrangement is expected to occur faster if steric interaction between 3- and 4-substituents exists in the 2-imino isomer. Another reaction may occur in acidic medium phenylimino-2-bipheny]-3,4-4-thiazoline hydrolyzed with hydrochloric acid gives the corresponding 4-thiazoline-2-one and aniline (717). 

The photochemical rearrangement of the mesolonic thiazole (33) provides an original synthesis of the 4-methylthio-derivatives of the A-4-thia2oline-2-one (34) (Scheme 15) (33). 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Pyridazin-3(2H)-ones rearrange to l-amino-3-pyrrolin-2-ones (29) and (30) upon irradiation in neutral methanol (Scheme 10), while photolysis of 5-amino-4-chloro-2-phenylpyridazin-3(2H)-one gives the intermediate (31) which cyclizes readily to the bis-pyridazinopyrazine derivative (32 Scheme 11). 

Hydroxy-6-methyl-2-phenylpyridazin-3(2Fr)-one and 4-hydroxy-5-nitropyridazin-3(2FT)-one rearrange in acidic medium to 3-methyl-l-phenylpyrazole-5-carboxylic acid and 4-nitropyrazole-5-carboxylic acid. 4-Hydroxypyridazin-3(2FT)-ones with a hydroxy group or other group at positions 5 or 6, which is easily replaced in alkaline medium, are transformed into 5-(or 3-)pyrazolones with hot alkali. An interesting example is ring contraction of 5-chloro-4-(methylthio)-l-phenylpyridazin-6(lFT)-one which gives, besides pyrazole derivative (127), 4-hydroxy-5-methylthio-l-phenylpyridazin-6(lFf)-one (128 Scheme 41). 

When alkoxypyridazine 1-oxides are heated alone or in the presence of p-toluenesulfonic acid the methyl group migrates from the methoxy group to the A-oxide group. In this manner, 4-methoxypyridazine 1-oxide rearranges to l-methoxypyridazin-4(l//)-one, 5-methoxypyridazine 1-oxide to 2-methylpyridazin-5(2//)-one 1-oxide and substituted 3,6-dimethoxypyridazine 1-oxides to l,3-dimethoxypyridazin-6(l//)-ones. 

Irradiation of the A-bromo- or N- chloro-azetidin-2-ones (71) in the presence of alkenes, alkynes or radical donors induces rearrangement to the /3-haloalkyl isocyanates (72) via a... 

Ring expansions of suitable /3-lactams can also be achieved on treatment with base rearrangement of the Af-substituted azetidin-2-ones (133) occurs in the presence of LDA to give (134) (72JA9261). Aminolysis of the /3-lactam epoxide (135) and the aldehyde (137) affords (136) and (138) respectively (81JHC1239). 

Several ring contraction routes to /3-lactams have been developed. One of the most important is the photochemical Wolff rearrangement of 3-diazopyrrolidine-2,4-diones (178), which provides a general route to 3-carboxyazetidin-2-ones (179). Lack of stereoselectivity is a problem, but facile epimerization is possible because of the electron withdrawing 3-substituent (78T1731). 

The chemistry of benzazetidin-2-ones (251) can also be explained in terms of facile ring opening to the iminoketenes (252) which dimerize, rearrange or can be intercepted by nucleophiles or in cycloadditions depending on the conditions. Indeed, this ring opening precludes their isolation in all but exceptional cases (Section 5.09.4.3.5) (76AHC(19)215). 

H -Azepin-2-one, 4-allyloxytetrahydro-Claisen rearrangement, 7, 508 1 H-Azepin-2-one, hexahydro-conformation analysis, 7, 499 mass spectra, 7, 501... 

H-Azepin-2-one, 3-acetyl-synthesis, 7, 542-543 3/f-Azepin-2-one, 7-acetyl-synthesis, 7, 542-543 3H-Azepin-2-one, 3-acyl-rearrangements, 7, 505 3/f-Azepin-2-one, 3-acyl-2-alkoxy-formation, 7, 542-543 3H-Azepin-2-one, 1-alkyl-rearrangements, 7, 505 3/f-Azepin-2-one, N-alkyl-synthesis, 7, 511 Azepinones... 

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