Pyridine-substituted hydroxythiophenes. I. Preparation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes.

2-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes and 4-(2-, 3- and 4-pyridyl)- 3-hydroxythiophenes have been prepared by hydrogen peroxide oxidation of the corresponding boronic esters. In the former case the boronic esters were obtained in three steps from 2,3-dibromothiophene via the corresponding 3-bromo-2-pyridylthiophenes synthesized by Pd(0)-catalyzed coupling between 3-bromo-2-trimethylstannylthiophene and the corresponding bromopyridines. In the latter case the known isomeric pyridylthiophenes were converted into the corresponding boronic esters in three steps via tribromo- and 3-bromo-4-pyridylthiophenes successively. 4-(3- and 4-pyridyl) thiophen-2(5H)-ones were also obtained in the syntheses of 4-(3- and 4-pyridyl)-3-hydroxythiophene. They are suggested to arise from rearrangement during the halogen-metal exchange. Spectroscopic investigations by 1H NMR and IR show that these hydroxythiophene systems exist exclusively as enol forms.     

Pyridine-substituted hydroxythiophenes. IV. Preparation of 3- and 4-(2-, 3- and 4-pyridyl)-2-hydroxythiophenes

3-(2-, 3- and 4-Pyridyl)-2-methoxythiophenes have been prepared in good yields through the Pd(0)-cat-alyzed coupling of the three isomeric bromopyridines with 3-trimethylstannyl-2-methoxythiophene. This compound was prepared through halogen-metal exchange of 3-bromo-2-methoxythiophene followed by stannylation. 3-Bromo-2-methoxythiophene was prepared by dibromination and α-debromination of 2-methoxythiophen. Most attempts to demethylate 2-methoxy-3-pyridylthiophenes using a large variety of reagents failed, probably due to the instability and high reactivity of the desired 3-pyridyl-2-hydroxythiophene systems. Only 2-methoxy-3-(3-pyridyl)thiophene reacted with boron tribromide to give 3-(3-pyridyl)-3-thiolene-2-one, which only was stable in ether solution at ?20°. The attempted demethylation of 2-methoxy-3-(2-pyridyl)thiophene with trimethylsilane chloride/sodium iodide in refluxing acetonitrile led to a dimer. Demethylation of the 2-methoxy-3-pyridylthiophenes with dibenzyl diselenide and sodium borohydride gave 3-pyridylthiophan-2-ones. A number of other routes to prepare 3-pyridyl-2-hydroxythiophenes were also explored, but none of them gave the desired compounds. On the other hand, the 4-(2-, 3-, and 4-pyridyl)-2-hydroxythiophene systems could easily be prepared by hydrogen peroxide oxidation of the corresponding 4-pyridyl-2-thiopheneboronic esters, which were obtained from 2-bromo-4-pyridylthiophenes by halogen-metal exchange followed by reaction with ethyl borate. The 2-bromo-4-pyridylthiophenes were prepared by dibromination of the known 3-pyridylthiophenes to the 2,5-dibromo derivatives, and removal of the 2-bromine by halogen-metal exchange at ?100°, followed by hydrolysis. The ¹H nmr and ir spectroscopic investigations show that these quite stable 2-hydroxythiophene systems exist exclusively in the 4-pyridyl-3-thiolen-2-one forms.     

Indole derivatives. 136. 4-, 5-, 6-, and 7-Nitro-3-indolesulfonic chlorides and sulfonamides

The reaction of nitroindoles with chlorosulfonic acid in the presence of sodium sulfate was used to synthesize 4-, 5-, 6-, and 7-nitroindole-3-sulfonyl chlorides. Under the influence of ammonia and several amines these compounds were convened to nitroindole-3-sulfonamides which were reduced with hydrazine hydrate in the presence of Raney nickel to the corresponding amines.See [1] for Communication 135.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1341–1345, October, 1990.     

Reactions of Polyhalopyridines. 17. Synthesis of 2-, 3-, and 4-Perfluoroalkylthiopolychloropyridines

2-, 3-, and 4-Perfluoroalkylthiopolychloropyridines have been synthesized using perfluoroalkylated thiol and disulfide derivatives of polychloropyridines via the thermal decomposition of Xe(II) bisperfluoroalkylcarboxylates. It was shown that their formation takes place from the starting thiols only through the formation of the disulfides. It was found that 3,4,5,6-tetrachloro-2-trifluoromethylthiopyridine reacts with potassium p-tolylthiolate with retention of the fluorine containing fragment and substitution of the chlorine atom in position 4 of the pyridine ring by the tolythio group.     

3, 6-endoxocyclohexanes and -cyclohexenes. XXV. Some reactions of dimethyl 4,5-(1-benzyl-1, 2, 3-triazoline)-3, 6-endoxohexahydrophthalate

The anhydride and dimethyl ester of 4, 5-(1-benzyl-1, 2, 3-triazoline)-3, 6-endohexahydrophthalic acid, having a triazoline ring with an exo-cis configuration, are synthesized by reaction of benzyl azide with the furan-maleic anhydride adduct. Opening of the triazoline ring under the action of hydrochloric and acetic acids takes place with the separation of nitrogen and formation of the chloro and acetoxy derivatives, respectively, unaccompanied by a Wagner-Meerwein type of rearrangement.Part XXIV, see [1].     

Steroids and sex hormones. 241. The partial synthesis of 3-methoxy--3-, 9- -oxido-7- hydroxy-11- -acetoxy-5- steroids

The preparation of the title compounds 11 , 37 , and 39 is described. 37 will serve as starting material for a partial synthesis of the steroidal alkaloid batrachotoxinin A ( 1 ).