Selectivity in cycloadditions—X : Regiochemistry of cycloadditions of nitrile oxides to thiophene and benzothiophene 1,1-dioxides

Thiophene-1,1-dioxide undergoes regioselective cycloaddition to benzonitrile oxide. In the reaction with the less reactive mesitonitrile oxide the sulfur dioxide deriving from the dimerization of the dipolarophile causes a catalytic decomposition of the nitrile oxide, which competes with the cycloaddition. Benzothiophene-1,1-dioxide and the vinyl sulfone system of 2,3-dihydrothiophene-1,1-dioxide and nitrile oxides with lower regioselectivity. The directing effect of the sulfonyl group has been elucidated with the aid of CNDO/2 calculations.     

Selectivity in cycloadditions-IX: Cycloadditions of nitrile oxides to indoles. Reactivity and regiochemistry

Cycloadditions of benzonitrile oxide and mesitonitrile oxide to N-methylindole and indole yield the acid sensitive cycloadducts 1 a-d with high regioselectivity. With N-carbethoxyindole the stable cycloadducts 1 e,f and minor amounts of the regioisomeric 2 e,f are isolated. The electron withdrawing substituent reduces both the regioselectivity and the reactivity of the cycloadditions.Frontier orbital considerations, based on MINDO/3 calculations, allow elucidation of the observed changes in reactivity and regiochemistry.     

K-region oxides and imines of benzo[b]phenanthro[2,3-d]thiophene and benzo[b]phenanthro[3,2-d]thiophene

The syntheses of the K-oxides and K-imine derivatives of benzo[b]phenanthro[2,3-d]thiophene and benzo-[b]phenanthro[3,2-d]thiophene are described. The parent hydrocarbons 1 and 2 were oxidized with osmium tetroxide and sodium metaperiodate, and the dialdehydes 12 and 18 so formed, cyclized to the corresponding epoxides 1a,12b-dihydrobenz[b]oxireno[9,10]phenanthro[2,3-d]thiophene ( 7 ) and 1a,12b-dihydrobenz-[b]oxireno[9,10]phenanthro[3,2-d]thiophene ( 13 ). Reaction of the oxiranes with sodium azide gave mixtures of azido-alcohols that, in turn, were transformed to the thiaarene imines 1a,12b-dihydro-1H-benz[b]azirino-[9,10]phenanthro[2,3-d]thiophene ( 8 ) and 1a,12b-dihydro-1H-benz[b]azirino[9,10]phenanthro[3,2-d]thiophene ( 14 ), respectively, with the aid of tri-n-butylphosphine.     

2,2′‐Bi[benzo[b]thiophene]: an unexpected isolation of the benzo[b]thiophene dimer

The crystal structure of 2,2′‐bi[benzo[b]thiophene], C₁₆H₁₀S₂, at 173 K has triclinic (P) symmetry. It is of interest with respect to its apparent mode of synthesis, as it is a by‐product of a Stille cross‐coupling reaction in which it was not explictly detected by spectroscopic methods. It was upon crystal structure analysis of a specimen isolated from the mother liquor that this reaction was determined to give rise to the title compound, which is a dimer arising from the starting material. Two independent half‐molecules of this dimer comprise the asymmetric unit, and the full molecules are generated via inversion centers. Both molecules in the unit cell exhibit ring disorder, and they are essentially identical because of their rigidity and planarity.     

Toluene dioxygenase-catalyzed cis-dihydroxylation of benzo[b]thiophenes and benzo[b]furans: synthesis of benzo[b]thiophene 2,3-oxide

Enzymatic cis-dihydroxylation of benzo[b]thiophene, benzo[b]furan and several methyl substituted derivatives was found to occur in both the carbocyclic and heterocyclic rings. Relative and absolute configurations and enantiopurities of the resulting dihydrodiols were determined. Hydrogenation of the alkene bond in carbocyclic cis-dihydrodiols and ring-opening epimerization/reduction reactions of heterocyclic cis/trans-dihydrodiols were also studied. The relatively stable heterocyclic dihydrodiols of benzo[b]thiophene and benzo[b]furan showed a strong preference for the trans configuration in aqueous solutions. The 2,3-dihydrodiol metabolite of benzo[b]thiophene was utilized as a precursor in the chemoenzymatic synthesis of the unstable arene oxide, benzo[b]thiophene 2,3-oxide.     

1H NMR spectra of benzo[b]furan,benzo[b]thiophene and benzo[b]selenophene oriented in a lyotropic mesophase

The proton nuclear magnetic resonance spectra of benzo[b]-furan, -thiophene and -selenophene oriented in a potassium laurate lyotropic liquid crystal have been analyzed. Geometrical information has been obtained and compared to previous thermotropic results and various hypothetical models.     

New reaction of benzo[b]thieno[3,2-b]benzo[b]thiophene disulfone

A new reaction of benzo[b]thieno[3,2-b]benzo[b]thiophene disulfone with amines that takes place with opening of one of the thiophene rings and nucleophilic substitution in the heteroaromatic ring at the site of cleavage of the S-C bond was observed. The molecular structures of the products of amination of the disulfone were determined by x-ray diffraction analysis. Hydrolysis and dehydration of the amination products gave derivatives of a new heterocyclic system, viz., benzo[b]-thieno[3,2-e]benzo[c]-1,2-oxathiin. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–323, March, 1980.     

Sulfur-rich heterocycles from 2-metalated benzo[b]thiophene and benzo[b]furan: synthesis and structure

The reaction of 2-lithiated benzo[b]thiophene with 8 equiv of elemental sulfur was found to give pentathiepino[6,7-b]benzo[d]thiophene. In contrast, treatment of 2-lithiated benzo[b]furan with sulfur under similar conditions produced the interesting ring system bis(benzo[4,5]furo)[2,3-e:3',2'-g][1,2,3,4]tetrathiocine. Both of these new cyclic polysulfides were studied by X-ray crystallography. Two polymorphic forms of pentathiepino[6,7-b]benzo[d]thiophene were found, displaying similar conformations but different packing schemes, which was also evident from powder diffraction data.     

NMR studies of sulphur heterocycles: III—13C spectra of benzo[b]thiophene and the methylbenzo[b]thiophenes

All carbon resonances in the title compounds have been unequivocably assigned. Steric effects in the peri substituted compounds have been compared with analogous effects in naphthalene and benzo[b]furan. The observed effects are not explained by current theory. Unusual deshielding steric shifts are observed at some carbons. Methyl substituent effects are not additive at any position in the sterically crowded 2,3-disubstituted compounds.     

Nucleophilic addition to benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxide

The reaction of benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxide with primary and secondary amines and with alcohols gave 10 b-amino- and 10 b-alkoxy-5a, 10b-dihydro-benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxides. These nucleophilic reagents do not add to benzo[b]thieno[2,3-b]benzo[b]thiophene S,S-dioxide.     

Enantioselective straightforward access to benzo[b]thiophene analogs of Azatoxin

Horner-Wadsworth Emmons olefination followed by asymmetric hydrogenation allowed the first synthetic access to the chiral thiotryptophan with good enantiomeric excess. Oxazolidinone formation followed by a Pictet–Spengler condensation provided the benzothiophenic analog of Azatoxin.     

A facile synthesis of benzo[b]thiophene derivatives

Lithiation of S-(2-methylphenyl) N,N,N',N'-tetramethylphosphorodiamidothioate with sec-BuLi at -105° gave the corresponding benzylic anion which was acylated with various aromatic esters to give various deoxybenzoin derivatives in moderate to high yields. Acidic treatment of these products in refluxing formic acid gave 2-arylbenzo[b]thiophene derivatives. 2-Methylbenzo[b]thiophene and benzo[b]thiophen-2(3H)-one were also prepared using the similar procedure.     

Synthesis and some transformations of benzo[b]thiophene derivatives

A number of 3-chloro-2-chlorocarbonylbenzo [b] thiophenes with alkyl substituants in various positions of the benzene ring were synthesized by arylation of acrylic acid with the corresponding alkyl-substituted iodobenzenes under the influence of catalytic amounts of palladium acetate and subsequent oxidation of the resulting arylacrylic acids with thionyl chloride. Replacement of the pyridine added in the oxidation reaction by triethylbenzylammonium chloride led to substantial increases in the yields of the desired products. The possibility of conversion of the resulting benzo [b] thiophene derivatives to thiophene ring-unsubstituted benzo[b] thiophenes was shown in the case of 3-chloro-2-chlorocarbonylbenzo [b] thiophene as a result of successive saponification of the 2-chlorocarbonyl group, decarboxylation, and dechlorination.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1618–1622, December, 1982.     

1H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene

The ¹H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene were recorded at 200MHz in two solvents, chloroform and acetone. A long-range coupling constant, 5J(HF), between the fluorine nuclei of the trifluoroacetyl group and H-3, of a value higher than 1 Hz, was measured. From the comparison of the ¹H chemical shifts of, and the solvent effects on, the trifluoroacetyl compounds and those of the corresponding 2-acetyl derivatives, and on the basis of an empirical interpretation of the ⁵J(HF) coupling constant, a predominant Z conformation was tentatively assigned to these derivatives.     

Synthesis of benzo[4,5]phenaleno[1,9-bc]thiophene and benzo[4,5]phenaleno[9,1–6c]thiophene

Two pentacyclic thiophenes, benzo[4,5]phenaleno[1,9–6c]thiophene ( 1 ) and benzo[4,5]phenaleno[9,1-bc]-thiophene (2) were synthesized via the corresponding 3-methylphenanthro[2,1-b]thiophene (7) and 1-methylanthra[2,1–6]thiphene ( 19 ).     

Synthesis of oxadiazoles, thiadiazoles and triazoles derived from benzo[b]thiophene

In this work 3-chloro-2-chlorocarbonylbenzo[b]thiophene (1) was prepared from cinnamic acid and then converted into the acid hydrazide 2. The azomethines 3a-e were prepared from the corresponding aryl aldehydes and the acid hydrazide 2. Treatment of compound 2 with formic acid gave the N-formyl acid hydrazide 4, which upon refluxing with phosphorous pentoxide or phosphorous pentasulphide in xylene yielded the corresponding 2- (3-chloro-1-benzothien-2-yl)-1,3,4-oxadiazole (5) and 2-(3-chloro-1-benzo-thien-2-yl)-1,3,4- thiadiazole (6). Reaction of 1-thiosemicarbazide 7 with NaOH leads to ring closure giving 5- (3-chloro-1-benzothien-2- yl)-4H-triazole-3-thiol (8) which is converted into a number of derivatives 9-12 Reaction of 2 with phenyl isothiocyanate and NaOH afforded 5-(3-chloro- 1-benzothien-2-yl)-4-(phenyl)-4H-1,2,4-triazole-3-thiol (14).     

Synthesis of tetraorgano-substituted silanes with the benzo[b]thiophene moiety

Catalytic dehydrocyclization of dimethyl(o-tolyl)- and dimethyl-4-(m-xylyl)-(benzo[b]thien-2-yl) silanes has given 11,11-dimethyl and 8,11,11-trimethyl-6,11-dihydro-11-silabenzo[b]naphtho[2,3-d]thiophenes, which were oxidized to the ketones. Previously unknown diorganobis(benzo[b]thien-2-yl)silanes have been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 419–422, March, 1989.