William T. Flowers

A convenient synthesis of 2,3,5,6-tetrahalogenopyridines and of 3,5-bis(alkylthio)pyridines from 2,6-diaminopyridine

Controlled chlorination of 2,6-diaminopyridine (1) affords 2,6-diamino-3,5-dichloropyridine (2a) which is then bis(diazotised) to give 2,3,5,6-tetrachloropyridine (3a); similarly prepared are other 2,3,5,6-tetra(chloro/bromo)pyridines and 2,6-dichloro-3,5-bis(thiocyanato)pyridine (3h), from which 3,5-bis(alkylthio)pyridines are easily obtained.

Novel aspects in the synthesis and acid-promoted cyclisation of some 2-diazo-2′-(p-tolylsulphonylamino)acetophenones: electrophilic displacement of an arylsulphonyl group from a sulphonamide

Under conditions where 2-(p-tolylsulphonylamino)benzoyl chloride (VIa) and diazomethane gave the expected diazo-ketone (VIIIa) in high yield, use of diazoethane gave only a low yield of the corresponding diazopropiophenone (VIIIb), contaminated by 2-methyl-N-(p-tolylsulphonyl)indoxyl (Xa). In contrast, 2-(N-methyl-p-tolylsulphonyl)benzoyl chloride (VIb) reacted with both diazoalkanes to give high yields of the expected diazoketones (VIIIe and f). 2-Diazo-2′-(N-methyl-p-tolylsulphonylamino)acetophenone (VIIIe) in acetic acid–acetic anhydride provided 3-acetoxy-2-acetyl-1-methylindole (XII) and toluene-p-sulphonic acid via novel electrophilic displacement of an arylsulphonyl group from the sulphonylamino-substituent; similar displacement from 2-diazo-2′-(p-tolylsulphonyloxy)acetophenone (Ih) was much more difficult.

Fluorocarbon derivatives of nitrogen. Part 19. Synthesis and mass spectrometric analysis of some pyridinium (tetrafluoro-4-pyridyl)-methylides

Abstract Nine new pyridinium methylides have been synthesised via S N Ar displacement of the 4-fluorine from pentafluoropyridine with pyridinium phenacylide [ → py + C(COPh)C 5 F 4 N-4] and a range of pyridinium alkoxycarbonylmethylides [ → py + C(CO 2 R)C 5 F 4 N-4, R = Me, Et, Pr n , Pr i , CH 2 CCl 3 , CH 2 CF 3 , CH 2 Ph, CH 2 CH 2 Ph]. A detailed analysis of the mass spectrometric fragmentation patterns for the alkoxycarbonyl compounds has been carried out. Spectroscopic data has also been obtained for pyridinium methylides synthesised from pyridinium ethoxycarbonylmethylide and 3-chlorotetrafluoropyridine or octafluorotoluene.

Unsaturated compounds containing nitrogen. Part 5. Reactions of 1,4-dichloro-1,4-diphenyl-2,3-diazabutadiene with nucleophiles

1,4-Dichloro-1,4-diphenyl-2,3-diazabutadiene (1) reacts with potassium cyanate to give 5-phenyl-1,2,4-triazol-3(2H)-one (9), but with potassium thiocyanate it gives the 1-chloro-4-thiocyanato-2,3-diazabutadiene (3). The thiocyanate (3) is not isomerized by heat, but is hydrolysed by acid to a mixture of 2,5-diphenyl-1,3,4-oxadiazole and 2-amino-5-phenyl-1,3,4-thiadiazole. Sodium hydrosulphide, potassium ethylxanthate, and thiourea all convert the dichlorodiazabutadiene (1) into 2,5-dipheyl-1,3,4-thiadiazole, while 2-aminobenzenethiol converts it into 2-phenylbenzothiazole.

Preparation and reactions of novel cyclic β-oxosulphonium salts obtained by the acid-induced cyclisation of 1-diazo-ω-phenylthio-2-alkanones

With perchloric acid, the diazo-ketones PhS[CH2]nCOCHN2(1a)–(1d) give the corresponding cyclic β-oxosulphonium salts (2a)–(2d); the p-chlorophenyl analogue of (2d) was similarly prepared. The salts (2a), (2c), and (2d) react with triphenylphosphine at C(2) to give the acyclic phosphonium salts (3a), (3c), and (3d) and, analogously, with potassium O-ethyl dithiocarbonate to give the corresponding acyclic O-ethyl dithiocarbonates (3f), (3g), and (3h). All the reactions of the salt (2b) with nucleophiles gave either 1-phenylthiobut-3-en-2-one (11) or products of its Michael addition. Salts (2c) and (2d) with sodium methoxide in methanol provide, respectively, methyl ω-phenylthio-butanoate and -pentanoate in a process that involves the loss of a methylene group. These and other reactions are considered to proceed via ylide intermediates; the intermediate derived by the deprotonation of (2d) being isolated, whereas that from (2c) rearranged to give 3-phenylthiocyclopentanone.

Unsaturated compounds containing nitrogen. Part 4. Further reactions of 1-chloro-2,3-diazabutadienes with S-nucleophiles

1-Chloro-1,4-diaryl-2,3-diazabutadienes (Ar1CClNNCHAr2), prepared by the reaction of thionyl chloride with aroylhydrazones (Ar1CONHNCHAr2), react with thiosemicarbazide or thiocarbohydrazide to give 2-arylidenehydrazino-5-aryl-1,3,4-thiadiazoles, and with potassium thiocyanate to give 1-thiocyanato-1,4-diaryl-2,3-diaza-butadienes which isomerize thermally to arylideneamino-5-aryl-1,3,4-thiadiazoles. 1-Chloro-1,4-diphenyl-2,3-diazabutadiene reacts with potassium ethylxanthate to give a 1-ethylxanthyl-2,3-diazabutadiene which on pyrolysis yields 2,5-diphenyl-1,3,4-thiadiazole.

Valence-bond isomer chemistry. Part 10. Kinetics and thermodynamics of the thermal gas-phase interconversion of hexakis(pentafluoroethyl)benzene and its para-bonded (‘Dewar’) isomer

The gas-phase interconversion of hexakis(pentafluoroethyl)benzene (1) and its para-bonded isomer (2) is a clean reversible isomerisation at 7–60 mmHg and 457–602 K. Measurements of the equilibrium constant give ΔH⊖= 37.6 ± 0.3 kJ mol–1 and ΔS⊖= 68.2 ± 0.5 J K–1 mol–1 for reaction (1), error limits being standard errors. The reaction at 457–525 K shows reversible first-order kinetics with the Arrhenius equations (i) and (ii) for the forward and backward reactions, respectively. The reaction is completely unaffected by packing the vessel with log10k1/s–1=(16.25 ± 0.12)–(186.6 ± 1.1) kJ mol–1/RT In 10 (i), log10k–1/s–1=(12.99 ± 0.16)–(151.7 ± 1.5) kJ mol–1/RT In 10 (ii) glass tubes or by adding but-2-ene to the system, and it is concluded that the interconversions are unimolecular. The reaction probably involves a biradical intermediate, and the rate-determining activated complex is similar in its structure to the para-bonded isomer rather than the benzene.

Alkyl aryl sulphides from the interaction of aryl thiocyanates and alcohols under the influence of triphenylphosphine or of trialkyl phosphites

Typical aryl thiocyanates react with primary alcohols in the presence of triphenylphosphine to give hydrogen cyanide, triphenylphosphine oxide, and the corresponding alkyl aryl sulphide in high yield. With propan-2-ol, yields of sulphide are lower on account of the competing elimination reaction which leads to a benzenethiol and propene. t-Butyl alcohol yields exclusively products of elimination. Alcohols in the presence of their phosphite esters give similar results, even with p-dimethylaminophenyl thiocyanate, the one thiocyanate studied that failed to give alkyl aryl sulphide with triphenylphosphine and simple primary alcohols. It is suggested that the observed products arise from collapse of a triphenyl- or trialkoxy-oxythiophosphorane which results from attack of an alcohol molecule on the first-formed triphenyl- or trialkoxy-arylthiophosphonium cyanide.

Polyfluorocarbanion chemistry. Part III. Reaction of hexafluoropropene with pentafluorobenzonitrile

Hexafluoropropene reacts with pentafluorobenzonitrile in the presence of caesium fluoride to give two mono-(2- and 4-), two di-(2,4- and 2,5-), and two tri-(2,4,5- and 2,4,6-)(perfluoroisopropyl) derivatives; no solvent is necessary. The 2,4,5-derivative rearranges to the less sterically hindered 2,4,6-derivative when heated with fluoride ion. The ring fluorine atoms in the perfluoroisopropyl derivatives are highly susceptible to nucleophilic displacement; the cyano-group resists hydrolysis.

Reaction of aromatic or heterocyclic amines and perfluoro-2-methylpent-2-ene to give fused pyridines, ketenimines, or enamines

Perfluoro-2-methylpent-2-ene (1) reacts with aromatic amines to give high yields of 4-arylaminoquino-lines; aminopyridines react similarly to give the corresponding derivatives of either naphthyridine or pyridopyrimidine, whereas aromatic primary amines with substituents in the ortho-positions, or t-butylamine, give ketenimines, dialkylamines give enamines, and ammonia gives a dicyano-enamine.