Search

Arylbenzenes: 3,4-dichlorobiphenyl reactant: Thirty-eight grams (0.1 mole) of bis-3,4-dichlorobenzoyl peroxide byproduct: 3,4-dichlorobenzoic acid solvent: 100 ml. of petroleum ether product: 3,4-dichlorobiphenyl byproduct: biphenyl Keywords: addition, to CO; arylation

Sulphonylnitrosamides ArSO2N(NO)R with RC2H5, n-C3H7, i-C3H7 and n-C4H9 undergo two types of decomposition in inert solvents at 95°, yielding a. nitrogen and alkyl arylsulphonate b. nitrogen, arylsulphonic acid and olefin. The rate of gas evolution is strictly first order. This is compatible with a nitroso-azo rearrangement as the rate-determining step. The resulting diazosulphonate decomposes quickly into the products of either a or b. Under the influence of acid arising from b, denitrosation becomes appreciable towards the end of reaction. Such denitrosation is not observed when RCH3, no acid (and olefin) being produced.

A comparative survey has been made of the products of homolytic decomposition of 2-(N-alkyl-N-phenyl-carbamoyl)benzenediazonium fluoroborates under a variety of conditions, and of those of photolysis of the corresponding N-alkyl-2-iodobenzanilides. Copper-catalysed decomposition of the diazonium salts in acetone purged with oxygen gives cyclohexadienones, the yields of which reflect the extent of radical cyclisation to γ-lactam intermediates. Decomposition of the diazonium salts induced by sodium iodide in methylene chloride containing a little added iodine gives cyclohexadienyl iodides, structures of which have been established by Ag+-catalysed methanolysis to cyclohexadienyl methyl ethers, and/or by photolysis, which gives cyclohexadienyl dimers.

The stereoisomeric 4′-hydroxy-2-methylisoindoline-1-spiro-1′-cyclohexadien-3-ones (1) rearrange with acid to give N-methylphenanthridinone (3) by migration of the aryl group and not of the nitrogen atom. However, similar reactions of the 2′-,3′-benzo- and 6′-hydroxy-4′-,5′-benzo-analogues [(21) and (7)] occur with predominant nitrogen migration. Brief exposure of compound (1) or (21) to methanolic acid results in the formation of cyclo-hexadienyl methyl ethers, presumably by way of intermediate cyclohexadienyl cations. It has not, however, been possible to identify a similar process in the acid-catalysed methanolysis of compound (7). The cyclohexadienyl ethers are also obtained when the corresponding cyclohexadienyl iodides are exposed to methanolic silver nitrate. Treatment of the stereoisomeric 4′-,5′-benzo-6′-iodo-compounds (34) with methanolic silver nitrate leads to one stereoisomer of the 6′-methyl ether (26) and to N-methylbenzo[c]phenanthridin-6-one (9). Stereospecific formation of the same isomer of (26) was observed when 2-(N-methyl-2-naphthylcarbamoyl) benzenediazonium sulphate was decomposed by heating in methanol. Possible factors controlling stereoselection in these reactions, and the competition between aryl and nitrogen migration, are briefly discussed.

The decomposition of N-methyl-4′-(methylthio)benzanilide-2-diazonium salts (VIII) gives 2-methylisoindoline-1-spirocyclohexa-2′,5′-diene-3,4′-dione (IV) and methanethiol, rather than the corresponding thione and methanol. Similarly, 4′-methoxy-N-methylbenzanilide-2-diazonium sulphate (VIII; O for S) decomposes in 18O-enriched water to give the dione (IV) with incorporation of 18O. This spiro-dienone forming reaction does not intervene in Pschorr cyclisations since trans-2-amino-α-(2- and 4-methoxyphenyl)cinnamic acids give 1- and 3-methoxyphenanthrene-10-carboxylic acid in high yield.Reduction of the spiro-dienone (IV) results in opening of the γ-lactam ring and aromatisation to biphenyls; thus its semicarbazone with potassium t-butoxide gave N-methylbiphenyl-2-carboxamide, and Clemmensen reduction gave 4′-hydroxy-N-methylbiphenyl-2-carboxamide (VII).The octahydro-derivative [bi-(2-methyl-3-oxoisoindoline-1-spirocyclohex-4′-yl)(XIV)] of an unsaturated dimeric product, (II), of an earlier diazonium decomposition has been synthesised, thus confirming the structure of this and analogous dimers.

The title reactions give the expected variety of products derived from the radicals formed by loss of iodine. The initial reactions of these radicals are identified as cyclisation to γ- and δ-lactam intermediates, together with a minor amount of 1,5-hydrogen transfer from the N-alkyl group. The δ-lactam intermediates are oxidised to N-alkyl-phenanthridinones, and 1,5-hydrogen transfer results in dealkylation at the nitrogen atom. The γ-lactam intermediates react by several pathways. That from the 2′-methoxy-amide predominantly dimerises, whilst from the 3′-methoxy-amide a major product is a spirocyclohexenone γ-lactam, the result of demethylation at the oxygen atom (possibly catalysed by hydrogen iodide liberated during the reaction).The γ-lactam intermediate from the 4′-methoxy-amide also suffers demethylation at the oxygen atom to give a spirocyclohexadienone γ-lactam; this is photoisomerised under the reaction conditions to the stereoisomeric cyclopentenones (23) and (24). Further products believed to be formed via this γ-lactam intermediate are 3-methoxy-N-methylphenanthridinone and 4′-methoxy-N-methylbiphenyl-2-carboxamide. The possibility is discussed that these two products may also arise by photoinduced rearrangement of a primary photoproduct.

Previously unidentified products formed in the catalysed decomposition of diazonium fluoroborates from amino-N-methyl-naphthanilides and -N-naphthylbenzamides are shown to include unsaturated spiro-dimers [(IV), (VI), (IX), (XIII), and (XV)], and a spiro-cyclohexadienone (III) in which an oxygen atom has been incorporated into the molecule. Products of deamination and demethylation and of normal ring closure are also formed but phthalimidines are not.

DEVELOPMENTS in the theory and practice of organic chemistry during the past ten years have opened up a new and broader outlook on organic reactions in general. The reactions of classical organic chemistry, which in the main are concerned with reactions between two molecules or with reactions between an ion and a molecule, have been embraced within a comprehensive electronic theory, the main features of which were firmly established about fifteen years ago. To-day many examples are known of reactions which do not possess the characteristic features of the electronic processes generally referred to as 'electrophilic' or 'nucleophilic', and it is now necessary to consider a third type of reaction, namely, those between a molecule and either an atom or a free radical. Provision for this third type of reaction is obviously necessary, since it is possible to sever a covalent bond in one of two ways, resulting in heterolysis or homolysis, thus