E.B. Pedersen

Relationship between the properties of radical cations and the rate constants and the substitution patterns in electrophilic aromatic substitution

Abstract By a charge transfer mechanism for electrophilic aromatic substitution the logarithmic plot of overall rate constants for substitution against ionization potentials is correctly predicted. Also, orientation of substitution is found to be correlated with the hyperfine coupling constants of the aromatic radical cation. The presence of radical cations under the conditions of electrophilic substitution is discussed.

Studies on organophosphorus compounds—VI : Dimethylamino-heterocyclic compounds from the corresponding potential hydroxy-compounds and HMPA

Abstract Potential hydroxy heterocyclic compounds are heated in HMPA at 220–230° for 20 min-15 h. The OH Group is thereby replaced by a dimethylamino-group and the yields for the reactions are indicated for the following compounds: 2-Dimethylamino-quinoline (79%); 2-dimethylamino-lepidine (77%); 2-dimethylamino-benzo[b]furan (47%); 2-dimethylamino-1-methyl-indole (68%); 2-di-methylamino-thiophene (3%); 2-dimethylamino-5-methyl-thiophene (23%); 3-dimethylaminobenzoisothiazole-S-dioxide (80%). When the reaction was performed in the presence of pyrrolidine, the following compounds were obtained: 3-(1′-pyrrolidyl)-benzoisothiazole-S-dioxide (70%); 2-(1-pyrrolidyl)-lepidine (35%). Bis(dimethylamido)-aryl-phosphates, which could be postulated as intermediates in the above reactions, were easily ruled out as such.

Studies on enethiols—V : Syntheses of α-thioacyllactones and α-thioacylthiollactones. Structure determination by NMR spectroscopy☆

Abstract α-Thioacyllactones and α-thioacylthiollactones have been prepared in moderate to good yields by action of H 2 S and HCl on the α-acyl-analogues. NMR and IR studies show that the aliphatic thioacyl compounds exist as equilibrium mixtures of the cis - and the trans -enethiol forms, whereas the thioaroyllactones are present exclusively as intramolecularly H-bonded cis -enethiols. The NMR spectra are discussed and the influence of different solvents on chemical shifts and coupling constants are also described and discussed. The syntheses and properties of some methylated and acetylated α-thioacyllactones are presented, and their absolute configurations determined by NMR spectroscopy.Abstract α-Thioacyllactones and α-thioacylthiollactones have been prepared in moderate to good yields by action of H2S and HCl on the α-acyl-analogues. NMR and IR studies show that the aliphatic thioacyl compounds exist as equilibrium mixtures of the cis- and the trans-enethiol forms, whereas the thioaroyllactones are present exclusively as intramolecularly H-bonded cis-enethiols. The NMR spectra are discussed and the influence of different solvents on chemical shifts and coupling constants are also described and discussed. The syntheses and properties of some methylated and acetylated α-thioacyllactones are presented, and their absolute configurations determined by NMR spectroscopy.

Thiophene chemistry—XX : C- and O-methylation of thallium(I)-salts of 3-thiolene-2-ones

Abstract Thallium(I) salts of thiolene-2-ones with no substituent in the 3-position on treatment with MeI underwent C-methylation in the 3-position. O-, Di- and trimethylation reactions were also observed. Analogous treatment of a 3-substituted 3-thiolene-2-one with thallium(I) ethoxide produced in addition to the expected thallium salt, a salt due to ring-opening. The tautomeric properties of 3,5-dimethyl-3-thiolene-2-one have been investigated.

Studies on organophosphorus compounds—IV: HMPA as precursor for dimethylamine in nucleophilic aromatic substitution reactions

Abstract The potential leaving groups (NO2, Cl, Br, OH, OMe) in nucleophilic aromatic substitution reactions are replaced by a dimethylamino group simply by heating the aromatic compounds (activated by cyano- or nitro-groups) in HMPA at elevated temperature.

Thiophene chemistry—XXII : Some reactions of benzo[b]thiophene-2(3H)one ☆

Abstract Benzo[b]thiophene-2(3H)one has been prepared from 2-t-butoxybenzo[b]thiophene by dealkylation. Alkylation of sodium, thallium and tetrabutylammonium salts of benzo[b]thiophene-2(3H)one produces both C- and O-alkylation along with products due to ring-opening. At elevated temperatures benzo[b]thiophene-2(3H)one reacts with HMPA (hexamethylphosphorictriamide) to give 2-dimethylaminobenzo[b]thiophene. Other 2-aminobenzo[b]thiophenes are produced by refluxing benzo[b]thiophene-2(3H)one in HMPA in the presence of excess of the corresponding amine.

Thiophene chemistry—XVI : Acid-catalyzed elimination reactions of 2-t-butoxy-3-thienyl carbinols

Abstract 2-t-Butoxy-3-thienyl carbinols have been prepared and their combined dealkylation and dehydration reactions studied. Treatment of the title compounds at 10° with dil HCl in dioxan-water solution produces 3-(1′-alkenyl)-2-t-butoxythiophenes. When the carbinols are heated to about 150° in the presence of p-toluenesulphonic acid, 3-(1′-alkenyl)-3-thiolene-2-ones and 3-alkylidene-4-thiolene-2-ones are formed. Mechanistic considerations for the dealkylation and dehydration reactions are given. A hetero-Diels-Alder reaction is presented which gives a new route to condensed heterocycles.Abstract 2-t-Butoxy-3-thienyl carbinols have been prepared and their combined dealkylation and dehydration reactions studied. Treatment of the title compounds at 10° with dil HCl in dioxan-water solution produces 3-(1′-alkenyl)-2-t-butoxythiophenes. When the carbinols are heated to about 150° in the presence of p -toluenesulphonic acid, 3-(1′-alkenyl)-3-thiolene-2-ones and 3-alkylidene-4-thiolene-2-ones are formed. Mechanistic considerations for the dealkylation and dehydration reactions are given. A hetero-Diels-Alder reaction is presented which gives a new route to condensed heterocycles.

Studies on organophosphorus compounds—VIII : The reaction of oximes with hmpa at elevated temperature☆

Abstract A new method for the preparation of nitriles by refluxing aldoximes in HMPA is presented. In the same reaction, almost quantitative yields of octamethylpyrophosphoric amide are formed. Reaction of oximes of aromatic ketones with HMPA produces Beckmann rearrangement products, the corresponding amidines and some quite anomalous products. Cyclohexanone oxime gives no Beckmann rearrangement but several products like octahydroacridines, octahydrocarbazoles, octahydrophenazines, phenazines, lutidines and N,N-dimethyl-anilines.

Studies on organophosphorus compounds—III: Reaction of α-substituted secondary car☐amides with HMPA—amidine and/or nitrile syntheses

Abstract Secondary car☐amides (R1CONHR2) undergo different reactions when heated in HMPA at about 220°. If R1 or R2 can form stable carbonium ions, fragmentation reactions are observed and the corresponding nitriles R2CN or R1CN, respectively, are formed. Also amidines are produced. N-benzyl-acetamide rearranges when heated in HMPA to give β-phenyl-propionitrile, It is suggested that in all the reactions investigated the first step is the formation of a phosphorodiamidate followed by formation of a nitrilium carbonium ion. The fragmentation reactions can be used as an alternative to the Sandmeyer reaction (nitrile synthesis).

Studies on organophosphorus compounds—V: Pyridines from secondary car☐amides and HMPA

Abstract A new pyridine synthesis has been found by refluxing certain simple secondary car☐amides in HMPA. Thus 2,6-dimethylpyridine, 2-ethyl-6-methylpyridine, 2,3,6-trimethylpyridine, 2-ethyl-3,6-dimethylpyridine, 2-benzyl-6-methyl-3-phenylpyridine, 2-ethyl-3-methyl-5,6,7,8-tetrahydroquinoline and 2-t-butyl-6-methylpyridine were prepared in 15–40% yield.