Brian Parton

Addition and cycloaddition reactions of β-chloroazo-olefins

2-Chloro-1-(2,4-dinitrophenylazo)ethene (1a) has been isolated, and the corresponding alkoxy-carbonylazo compounds (1b) and (1c) have been generated in solution, as the first examples of azo-olefins bearing single β-halogeno substituents. The compounds (1a) and (1b) undergo [4 + 2] cycloaddition to indene and to ethyl vinyl ether with high endo stereoselectivity. Furan and cyclopentadiene give the cycloadducts (6) and (7), respectively, with (1a). Nucleophilic addition–elimination reactions are observed with piperidine, indole, thiophenol, and carbanions. In most of these reactions the primary products are subject to further nucleophilic attack: thus, the hydrazones (11) formed by addition of carbanions are converted into aminopyrroles (12) by further reaction with the carbanions and dehydration.

Formation of pyrroles from β-chloroazoalkenes and 1,3-dicarbonyl compounds

Abstract The azoalkenes (1) have been prepared from the corresponding hydrazones of dichloroacetalhyde; they react with 1,3-dicarbonyl compounds to give first the addition-elimination products (4) and then pyrroles (6).

Nucleophilic aromatic substitution: transmission of substituent effects in alkaline hydrolysis of 4-aminophenylazobenzothiazolium dyes

Alkaline fading of 2′-, 5-, and 6-substituted 2-(4′-aminophenyl)azobenzothiazolium dyes (I) possesses [graphic omitted] a second-order rate constant (kOH). The value of kOH is shown to predicted by equation (i) where σN is log kOH= 0.76σN+ 0.24σS+ 1.69σ++ log[10–0.15(pK–9.5)/(1 + 100.25(pK–9.5))]+ 0.74 (i)σ+ for 6- and σ for 5-substituents, σs is σ– for 5- and σ for 6-substituents, σ+ is for 2′-substituents, and the pK is that of the leaving 4′-amine. The dye fading is not very sensitive to substituents in the benzothiazole phenyl ring but the charge is transmitted more effectively through nitrogen than through sulphur.

The activating effects of arylazo groups on a double bond. Preparation and properties of some bis(diaikylamino)arylazoethenes and related compounds

The 1,1-dichloro-2-arylazoethenes (1) readily undergo conjugate addition–elimination reactions with amines to give the new azo-olefins (3). The n.m.r. and electronic spectra of these compounds, which are highly coloured crystalline solids, indicate that they are strongly polarised enamines. The azo-olefin (3h) is formed from compound (1a) and thiophenol in sodium hydroxide, but in the presence of sodium carbonate the hydrazone (8a) is formed instead. 4-Chlorophenol gives the analogous hydrazone (8b). Compound (3h) is reduced by thiophenol to the hydrazone (9).