Pd‐Catalyzed C—S Cyclization via C—H Functionalization Strategy: Access to Sulfur‐containing Benzoheterocyclics

A C—H sulfurated cyclization protocol starting from thioacetates is developed for straightforward construction of sulfur‐containing benzoheterocyclics. The diversiform functional dihydrobenzothiophenes and thiochromans were comprehensively achieved through the Pd‐catalyzed carbon‐ sulfur cyclization. Mechanistic studies indicated that C—H bond cleavage was involved in the rate‐determining step. [1]Benzothieno‐[3,2‐b]‐ [1]benzothiophene (BTBT) and benzo[b]thieno[2,3‐d]thiophene (BTT) were efficiently established as the well‐known organic field‐effect transistor (OFET) material molecules through this methodology.     

锂硫电池用高度环化硫化聚丙烯腈的制备

硫化聚丙烯腈因其不溶解机制和有效缓解锂硫电池中多硫化物“穿梭效应”,被认为是具有吸引力的锂硫电池正极候选材料。硫化聚丙烯腈的导电聚合物骨架具有优异的电子导电性,同时共轭主链能有效解决充放电过程中硫正极体积变化引起的正极结构坍塌问题。因硫化聚丙烯腈的固-固反应机理,有效克服了传统硫正极在醚类电解液中多硫化物溶解及穿梭效应的问题,具有高正极活性物质利用率、出色的循环稳定性和结构稳定性等优势。有许多研究工作致力于通过硫化促进剂来提高硫化聚丙烯腈的硫含量,进而提高材料的能量密度。其中,硫化聚丙烯腈主链的环化度与循环稳定性的关系引起了我们的关注。在该研究工作中,通过在硫化过程中引入无水硫酸铜和正乙基正苯基二硫代氨基甲酸锌(ZDB)合成了SPAN-C-V复合材料。无水硫酸铜和ZDB的共同引入降低了聚丙烯腈环化反应的起始温度,同时提高了产物SPAN-C-V内碳碳双键的含量,在提高了材料硫含量的同时提高了其环化度。以SPAN-C-V为正极活性物质所组装的锂硫电池展现出良好的循环稳定性和倍率性能：在0.2 C (1 C = 600 mAh·kg^-1)下循环100次后的可逆容量为601 mAh·kg^-1,容量保持率为93%。该工作对于硫化聚丙烯腈材料的发展提供了参考。     

Redox regulation of protein tyrosine phosphatase 1B (PTP1B): a biomimetic study on the unexpected formation of a sulfenyl amide intermediate

The effect of steric and electronic environments around the sulfur and nitrogen atoms and the role of nonbonded S...O/N interactions on the cyclization reactions of amide substituted benzene sulfenic acids are described. The reaction profiles and the role of different substituents on the cyclization are investigated in detail by theoretical calculations. It is shown that the synthetic thiols having ortho-amide substituents may serve as good models for the enforced proximity of the amide and cysteine thiol groups at the active site of protein tyrosine phosphatase 1B (PTP1B). However, some of the sulfenic acids derived from such models do not effectively mimic the cyclization of protein sulfenic acids. This is mainly due to the requirement of very high energy for breaking the S-O bond to form a planar five-membered ring of isothiazolidinone. It is shown that the sulfenic acid having two substituents-an amide moiety and a heterocyclic group-in the ortho-positions undergoes a rapid cyclization reaction to produce the corresponding sulfenyl amide species. These studies reveal that the introduction of a substituent at the 6-position of the benzene ring enhances the cyclization process not only by facilitating a closer approach of the -OH group and the backbone -NH moiety but also by increasing the electrophilicity of the sulfur atom in the sulfenic acid.     

Phosphine-catalyzed construction of sulfur heterocycles

A simple and efficient method for constructing sulfur heterocycles was developed using a phosphine-catalyzed tandem umpolung addition and intramolecular cyclization of bifunctional sulfur pronucleophiles on arylpropiolates. The reaction offers a promising route to synthetically useful as well as biologically active heterocycles under neutral conditions.     

Alkyne Versus Ynamide Reactivity: Regioselective Radical Cyclization of Yne‐Ynamides

Ynamides are typically more reactive than simple alkynes and olefins. However, a serendipitous observation revealed a rare case where the reactivity of simple alkynes exceeds that of ynamides. This led to the development of a unique sulfur‐radical‐triggered cyclization of yne‐tethered ynamides, which involves attack of the alkyne by a thiyl radical followed by cyclization with the ynamide. A wide range of novel 4‐thioaryl pyrroles that could tolerate common functional moieties and N‐protecting groups were expediently constructed by this strategy. The current method contrasts with the typical cyclization of yne‐ynamides, which involves the attack of the alkyne moiety by the ynamide core. Control experiments and DFT calculations supported the participation of the sulfur radical in the reaction and the regioselective cyclization. The synthetic potential of the substituted pyrroles is also discussed.     

Efficient Synthesis of Cyclic Sulfoximines from N-Propargylsulfinamides through Sulfur–Carbon Bond Formation

Cyclic sulfoximines were readily synthesized by the cyclization of N-propargylsulfinamides without using expensive and toxic metal catalysts. This cyclization proceeded without loss of optical purity of chiral sulfinamides through the unusual sulfur–carbon bond formation promoted by an inexpensive inorganic base. This stereospecific cyclization offers a general approach to the asymmetric synthesis of chiral cyclic sulfoximines as an emerging heterocycle in medicinal chemistry.     

Synthesis of 2,3-disubstituted benzo[b]thiophenes via palladium-catalyzed coupling and electrophilic cyclization of terminal acetylenes

2,3-Disubstituted benzo[b]thiophenes have been prepared in excellent yields via coupling of terminal acetylenes with commercially available o-iodothioanisole in the presence of a palladium catalyst and subsequent electrophilic cyclization of the resulting o-(1-alkynyl)thioanisole derivatives. I(2), Br(2), NBS, p-O(2)NC(6)H(4)SCl, and PhSeCl have been utilized as electrophiles. Aryl-, vinyl-, and alkyl-substituted terminal acetylenes undergo this coupling and cyclization to produce excellent yields of benzo[b]thiophenes. (Trimethylsilyl)acetylene also undergoes this coupling/cyclization process with I(2), NBS, and the sulfur and selenium electrophiles to afford the corresponding 2-(trimethylsilyl)benzo[b]thiophenes. However, cyclization of the silyl-containing thioanisole using Br(2) affords 2,3-dibromobenzo[b]thiophene.     

Cyclocopolymerization of diallyl ether with sulfur dioxide in acetone

The radical polymerization of diallyl ether (DAE) with sulfur dioxide produced soluble copolymers whose composition was between 1:1 and 2:1 in SO₂. The overall rate was maximum at a 2:1 feed composition in SO₂. A cyclocopolymerization scheme, which was based on cross propagations and the intramolecular cyclization of DAE radical, was applied. The energy of activation was larger for the uncyclized DAE radical in undergoing the cross propagation with SO₂ than in undergoing the intramolecular cyclization with the pendent allylic group by 40 kJ/mol. Formation of rings made of DAE and SO₂ and 3,4-disubstituted-tetrahydrofuran rings by the cyclized DAE units on the main chain was proposed on the basis of the ¹H-NMR spectra.     

Microwave-Assisted Syntheses of 2-Phenylbenzothiazoles

A new and easy synthetic route to 2-phenylbenzothiazoles has been achieved by direct thiation of benzoyl derivatives of aniline, various substituted anilines, and 1-naphthylamine under microwave irradiation. The oxidative cyclization using elemental sulfur in the presence of a catalytic amount of iodine is inexpensive and worked well for a number of anilides.     

Heterocycles. CXXVII. Action of sulfur on some heterocyclic compounds. Formation of thioamides,oxidative cyclization and thiation

The formation of heterocyclic thioamides from alkylpyridines, heteroaromatic amines and sulfur was investigated. Oxidative cyclization of these thioamides afforded the corresponding thiazoloazines. Attempted thiation of some hydrazones gave triazolopyridines and some examples of direct thiation of heterocycles are given.     

Sulfur ylides 13. Synthesis and intramolecular cyclization of keto-stabilized sulfur ylides

Keto-stabilized sulfur mono-and bisylides were obtained from N-phthalylglutamic acid and their intramolecular cyclization was studied. The intramolecular cyclization of the ylide obtained at the α-carboxy group gave a product of the pyrrolizidinedione structure; bisylide yielded a cycloheptene derivative as the result of intramolecular recombination of intermediate dicarbene. The ylide obtained at the γ-carboxy group underwent no cyclization, giving methylthio ketone and oxo benzoate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2771–2776, December, 2005.     

Sulfur ylides 8.* synthesis of 5-methylthio-7,8-dihydro-4,8a-diazfluorene-6,9-dione

Intramolecular cyclization of ketostabilized sulfur ylide obtained from β-alanine and 2,3-pyridinedicarboxylic anhydride was studied. The structure of the reaction product, 5-methylthio-7,8-dihydro-4,8a-diazafluorene-6,9-dione, was established by X-ray diffraction analysis. For Part 7, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2376–2378, November, 1998.     

Synthesis of 3-S-hetaryl-substituted pyridin-2(1H)-ones and 5,6-dihydropyridin-2(1H)-ones*

A method has been developed for the synthesis of 3-S-hetaryl-substituted pyridin-2(1H)-ones and 5,6-dihydropyridin-2(1H)-ones based on the base catalyzed cyclization of N-(3-oxoalkyl)- and N-(3-oxoalkenyl)amides which contain a divalent sulfur atom in an α-position to a carbamoyl group and bound to the heterocycle.     

Radical-mediated 5-exo-trig cyclizations of 3-silylhepta-1,6-dienes

Regioselectivity of the sulfonyl radical mediated 5-exo-trig cyclization of 3-silylheptadienyl systems 3a-d has been studied. At low temperature, the reaction of the sulfonyl radical occurs regioselectively at the allylsilane terminus, while a reversal of regioselectivity is observed at 80 degrees C. This general trend has been rationalized on the basis of polar effects and radical stabilization. Thiyl-mediated radical cyclization of dienes 3a, 3c-d, 7 with subsequent sulfur atom transfer was also studied, providing thiabicyclo[3.3.0] skeleton in one step with excellent stereocontrol.     

Understanding (the lack of) homolytic substitution chemistry of sulfones

High level calculations suggest that homolytic substitution (S(H)2) by alkyl radicals at sulfur proceeds through a mechanism that is assisted and dominated by LP → SOMO interactions; in the absence of these interactions, S(H)2 chemistry at sulfur is predicted to be virtually impossible. G3(MP2)-RAD calculations suggest that cyclization of the tert-butylsulfonylbutyl radical 2 (n = 2) proceeds with a rate constant of 1.7 × 10(-24) s(-1) at 80°, some 28 orders of magnitude slower than its sulfide cousin (n = 0).     

New approach to the synthesis of 2-carbamoylbenzothiazoles

The reactions of substituted anilines with chloroacetamide and sulfur in the presence of triethylamine afforded monothiooxamides. When treated with K₃Fe(CN)₆, the latter underwent cyclization to form 2-carbamoylbenzothiazoles. The reactions were accompanied by the formation of the corresponding thiooxanilic acids, which also underwent cyclization to form benzothiazole-2-carboxylic acids.     

Reactions of sulfur halides with unsaturated compounds. 26. Reactions of sulfur dichloride with tricyclo[4.2.2.02,5]deca-3,7-dienes and tricyclo[4.2.2.02,5]deca-3,7,9-trienes. Synthesis of compounds with a novel thiaskeletal structure

Addition of sulfur dichloride to tricyclo[4.2.2.0^{2, 5}]deca-3,7-dienes and tricyclo[4.2.2.0^2,5] deca-3,7,9-trienes is accompanied by intramolecular cyclization to give high yields of adducts with the novel thiaskeletal 7-thiatetracyclo[4.2.2.0^4,8.0^5,10]undecane structure. In the reaction of SCl₂ with the 2,3-endo, endo-diester (V), intramolecular cyclization is accompanied by lactonization, to give quantitative yields of the thiaskeletal chlorolactone (X). The structure of the latter compounds was established by x-ray diffraction examination.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 858–864, April, 1990.For previous commmunication see [1].     

Orientation and mechanism of reactions of aromatic amines with sulfur monochloride

The reaction of m-substituted anilines with sulfur monochloride has been studied. It has been shown that cyclization with the formation of 1, 3, 2-benzothiazathiolium compounds takes place in the position para to the substituent. The introduction of methoxy groups into o-nitroanilines interferes with the displacement of the nitro group by the chlorine atom. A nucleophilic reaction mechanism has been proposed according to which the nitro group is displaced after the formation of the thiathioniaazine ring.     

An approach to the phenanthrene nucleus via thionium ions and epoxyketone cyclizations

A sulfur version of a directed aldol-type condensation followed by a cyclization of an α,β-epoxyketone produces the phenanthrene nucleus, common in many natural products.     

Intramolecular cyclization of acyl radicals onto the azido group: a new radical approach to cyclized lactams

[reaction: see text] Aryl- and alkyl-derived azidoacyl radicals, generated from thiolesters by intramolecular homolytic substitution at the sulfur, can undergo five- and six-membered cyclization onto the azido moiety to give cyclized lactams.