Silvano Bozzini

Reactions of conjugated arylazocycloalkenes with grignard reagents—43: Parallel and antiparallel attacks of grignard hydrocarbon moiety on some arylazocycloalkenes

Abstract Conjugated phenylazocycloalkenes sterically hindered towards the antiparallel attach react with PhMgBr via parallel attack, to givesyn-phenylhydrazones. When such a sterical hindrance is absent in the azoalkenes, the reaction occurs via antiparallel attack even when the arylmagnesium bromide bears a particularly hindering aryl group. The conformation of thesyn-phenylhydrazones obtained by the above reactions and those of the corresponding ketones are discussed with the aid of the benzylic proton NMR analysis.

The mechanism of an unusual reaction of ortho-substituted azobenzenes with grignard reagents

Abstract 2-Methoxy- and 2-methyl-azobenzene reacted with aromatic Grignard reagents giving 2-methoxy-2′,6′-diaryl- and2-methyl-6-aryl-azobenzene respectively. The mechanism of these arylation reactions was investigated. Evidence for a mechanism of 1,4-addition involving the azo group, followed by elimination of magnesium bromohydride is reported.

Reactions of conjugated phenylazoalkenes with anionic reagents—5: Anty-phenyihydrazone derivatives

Abstract Conjugated phenylazoalkenes add anionic reagents to give 2-substituted anti phenylhydrazones, as demonstrated by 1 H NMR spectroscopy and, in some cases, by comparison with authentic samples.

Reactions of conjugated phenylazoalkenes with aliphatic amines. syn- and anti-phenylhydrazone derivatives

Abstract Conjugated phenylazoalkenes react with aliphatic amines to give mixtures of syn - and anti -phenylhydrazones, the composition of which is solvent dependent. A mechanism for these reactions is proposed. The structures of the products were determined by spectroscopic methods.

Reactivity of conjugated azoalkenes towards α-amino acid ethyl esters

The synthesis of Z- and E-arylhydrazones by 1,4-conjugate addition of glycine, L-alanine and L-tyrosine ethyl esters to phenylazostilbene 1, p-nitrophenylazostilbene 2 and p-nitrophenylazocyclohexene 3 is described. Optically active N-functionalized 2-aminocyclohexanones 22–26 are obtained by TiCl3 catalysed hydrolysis of the corresponding hydrazones. However, they have been shown to be unstable, as they undergo easy oxidation by air. X-Ray analysis of the phenylhydrazone 8a in the Z configuration is also reported.

Aromatic azocompounds—VI: Further experiments pertaining to the aromatic arylation of ortho-substituted azobenzenes by Grignard reagents

Abstract The aromatic arylation of ortho-substituted azobenzenes with phenylmagnesium bromide has been investigated. 2,2′-Disubstituted symmetric azobenzenes do not undergo the reaction. 2-Methoxy-6-methyl- and 2-methoxy-2′-methyl-azobenzene give 2-phenyl-6-methyl- and 2-methoxy-2′-methyl-6′-phenyl-azobenzene, respectively. Comparison of the behaviour of 2-methyl-, 2-ethyl- and 2-phenyl-azobenzenes shows that the larger the substituent in the azo derivative, the lower the reactivity of the latter towards arylation. The results obtained support the mechanism previously reported.

Reactions of conjugated arylazocyclohexenes with Grignard reagents; X-ray crystal structure of 1-hydroperoxy-1-(o-methoxyphenylazo)-2-phenylcyclohexane

Conjugated arylazocyclohexenes react with aromatic and aliphatic Grignard reagents to furnish 2-aryl- and 2-alkyl-cyclohexanone arylhydrazones having the syn-configuration with the 2-substituent axially oriented. Their structures have been established by chemical and spectroscopic methods. These compounds, as well as the anti-isomers, undergo ready autoxidation to give arylazo-hydroperoxides. The structure of 1-hydroperoxy-1-(o-methoxyphenylazo)-2-phenylcyclohexane has been determined by X-ray analysis.

Reactions of conjugated arylazocycloalkenes with Grignard reagents. Part 3. A convenient synthesis of 2,6-diaryl- and 2-alkyl-6-aryl-cyclohexanones

A synthesis of the title compounds with the substituents at C-2 and C-6 trans to each other is described. 2-Aryl-cyclohexanones were converted into 1-phenylazo-6-arylcyclohexenes, which by reaction with Grignard reagents led to trans-2,6-diaryl- and trans-2-alkyl-6-aryl-cyclohexanone phenylhydrazones. These compounds by oxidative hydrolysis furnished the corresponding trans-ketones, which were readily epimerised into the more stable cis-isomers.

Reactions of conjugated arylazocyclohexenes with Grignard reagents. Part 2. A new stereospecific route to 2-alkyl- and 2-aryl-cyclohexanones

4-Methyl- and 4-t-butyl-1-arylazocyclohexenes react with aliphatic and aromatic Grignard reagents, to furnish, after oxidative hydrolysis of the intermediate aryihydrazones, 2-alkyl-4-methyl-, 2-aryl-4-methyl-, 2-alkyl-4-tbutyl-, and 2-aryl-4-t-butyl-cyclohexanones, with a trans-configuration. From the reactions with o-tolyl- and α-naphthyl-magnesium bromide only the cis-isomers were obtained. The structures of the products were, determined by spectroscopic methods and by epimerization of the trans-cyclohexanones into the more stable cis-isomers.