Les reactions de transposition photochimique en serie heterocyclique—IV: Photo-isomerisation des phenyl-methyl thiazoles et isothiazoles isomeres

The photochemical behaviour of twelve phenylmethylthiazole isomers is identical to that of non-methylated products. Thus, in order of decreasing reactivity we have: 2-phenylthiazole or 5-phenylisothiazole > 5-phenylthiazole or 3-phenylisothiazole > 4-phenylthiazole or 4-phenylisothiazole. The two latter undergo photoisomerization only to a slight extent.Most of the rearranged compounds (95%) are formed either by a valence bond isomerization mechanism via bicyclic intermediates where the phenyl group is conjugated to the cycle, or by the Kellogg mechanism, through a 180° rotation around the bonds adjacent to the sulphur atom.These results have furthermore allowed us to confirm the selective action of iodine in these isomerization reactions.     

Elastic π±-d and π±-4He scattering below 70 MeV

Elastic scattering differential cross section data of ^± d at 65 MeV and ^{± 4}He at 51 MeV are presented and compared respectively to fully relativistic 3-body and optical potential calculations including true pion absorption.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

S-Alkylation en série hétérocyclique par catalyse par transfert de phase: thioalkyl-2-thiazoles,thioalkyl-2-Δ-4-thiazolines et thioalkyl-2-benzothiazoles

S-Alkylation in heterocyclic serie by phase transfer catalysis: 2-alkylthiothiazoles, 2-alkylthio-Δ-4-thiazolines and 2-alkylthiobenzothiazoles Some Δ-4-thiazoline-, thiazolidine-, and benzothiazoline-2-thiones have been S-alkylated by phase transfer catalysis; yields averaged 80 to 90%. With halogenated heterocyclic compounds of poor reactivity, the main reaction consisted in a dequaternization of the catalyst by the thiones acting as nucleophiles.     

Etudes photochimiques en série hétérocyclique. V. Mise en évidence d'oxazoles par photooxydation de thiazoles

Formation of oxazoles as by-products of photooxydation of thiazoles In the presence of air, light (high pressure mercury lamp) and iodine as sensitizer, benzene solution of arylthiazoles 2 , 3 and 13 (see scheme 1) were converted into a mixture of photoisomers and aryloxazoles (see scheme 2). Upon shorter times of irradiation under oxygen in chloroform containing methylene blue as a sensitizer 2,4,5-triphenylthiazole (7) is converted in 2,4,5-triphenyloxazole. Under usual photooxidation conditions, in methanol as solvent, most of arylthiazoles studied gave a mixture of nitriles, amides, acids esters and diketones. In the case of thiazole 7 , the corresponding oxazole was also found. A possible mechanism for the photochemical oxidation of arylthiazoles to aryloxazoles, via 2,5- and 4,5-endo-peroxides, may be proposed (see schemes 5 and 6).     

Electronic Absorption and Emission Spectra of 1, 3-Diaryltriazenes

The Pariser-Parr-Pople (PPP) type LCI-SCF-MO calculations were used to study the models of 1, 3-diphenyltriazene (1) , 1, 3-bis(3-pyridyl)triazene (2) , 1, 3-bis (2, 4-dichlorophenyl)triazene (3) , and 1, 3-bis (4-ethoxycarbonyl)triazene (4) . The results of the calculations were compared with the experimental electronic absorption and emission (fluorescence, phosphorescence) spectra of these compounds.     

Synthèse et étude physico-chimique de sulfures,sulfoxydes et sulfones en série thiazolique

The alkylation of Δ⁴-thiazoline-2-thiones under phase transfer catalysis conditions leads to the corresponding thioethers in good yields. The oxidation of 2-alkylthiazoles with m-chloroperbenzoic acid leads to the corresponding sulfines or sulfones depending on experimental conditions in yields of about 80-90%. The characteristic gle, tlc, ir, ¹H nmr and ms data are reported for most of the compounds studied.     

Etude dans la série des radicaux hétérocycliques. Partie XV. Décomposition aprotique de l'amino-6-éthyl-2-benzothiazole dans des substrats aromatiques et hétéroaromatiques: préparation des mésityl-6- et furyl-6-éthyl-2-benzothiazoles,des sels quaternaires et des spiropyrannes correspondants

Study of heteroaromatic radicals. Part XV .

1 Partie XIV: cf. [1].

Aprotic decomposition of 6-amino-2-ethylbenzothiazole in aromatic and heteroaromatic substrates: preparation of 6-mesityl- and 6-furyl-2-ethylbenzothiazoles and of the corresponding quaternary salts and spyropyrans In the presence of excess isopentyl nitrite in aprotic solvent, the 6-amino-2-ethyl-benzothiazole leads to 6-aryl- and 6-heteroaryl-2-ethylbenzothiazoles 1 to 14 in ca. 20–50% yield (Scheme 1, Table 1). The 2-ethyl-6-benzothiazolyl radicals generated during these reactions exhibit a weak electrophilic character (Table 2). Preparatively this method has been applied to the synthesis of 6-mesityl- and 6-furyl-2-ethylbenzothiazoles 6 and 7 , which were used to prepare the corresponding quaternary salts 15 , 16 and the spiropyrans 19, 20 (Scheme 4).