Cascade Synthesis of Benzothieno[3,2-b]indoles under Oxidative Conditions Mediated by CuBr and tert-Butyl Hydroperoxide

Controllable Synthesis of Benzo[b]furo[2,3-d]azepines or Furo[3,2-b]indoles via Intermolecular Oxidative Annulation of 2-(Furan-2-yl)anilines and Propargyl Carbonates versus Intramolecular C-H Amination Reactions

Two novel Pd-catalyzed protocols for the controllable synthesis of benzo[b]furo[2,3-d]azepines and furo[3,2-b]indoles have been developed by intermolecular oxidative annulation of 2-(furan-2-yl)anilines and propargyl carbonates versus intramolecular C-H amination reactions. These two protocols feature great scalability, functional group tolerance, and relatively mild reaction conditions. Notably, the robust methodologies could also provide valuable opportunities for assembling azepine-fused benzothiophene, indole-fused benzothiophene, and indole-fused benzimidazole, which may have potential applications in the synthesis of related pharmaceuticals or polymeric materials.

EtOS2K as a C1 Source: Solvent- and Temperature-Controlled Selective Synthesis of Quinoline-2-thione and Quinoline-2-one Derivatives

Herein, we disclosed a highly chemoselective synthesis of quinoline-2-one and quinoline-2-thione derivatives using EtOS2K as the C1 source. Quinoline-2-one derivatives were synthesized selectively with NaCl as a catalyst in the solvent DMSO/H2O, while quinoline-2-thione derivatives were produced without the need for any catalyst in an environmentally friendly solvent EtOH/H2O. The reaction conditions were mild and had good functional group tolerance.

Synthetic exploration of electrophilic xanthylation via powerful N-xanthylphthalimides

Organic xanthates are broadly applied as synthetic intermediates and bioactive molecules in synthetic chemistry. Electrophilic xanthylation represents a promising approach but has rarely been explored mainly due to the lack of powerful electrophilic reagents. Herein, synthetic exploration of electrophilic xanthylation via powerful N-xanthylphthalimides was investigated. This strategy might provide a new avenue to less-concerned but meaningful electrophilic xanthylation in organic synthesis. With the help of these powerful reagents, electrophilic xanthylation of a wide range of substrates including aryl/alkenyl boronic acids, β-keto esters, 2-oxindole, and alkyl amines, as well as previously inaccessible phenols (first report) was achieved under mild reaction conditions. Notably, this simple electrophilic xanthylation of alkyl amine substrates will occur in the desulfuration reaction, consistent with the previously reported methods. Similarly, xanthamide and thioxanthate groups could also be transformed into desired nucleophiles via this electrophilic reagent strategy. The broad substrate scope, excellent functional group compatibility and late-stage functionalization of bioactive or functional molecules made them very attractive as general reagents which will allow rapid incorporation of SC(S)R (R = OEt, Oalkyl, NEt2 and SEt) into the target molecules.

Synthesis of New Fused 4H-Thieno[3,2-b]pyrrole Derivatives via Decomposition of Methyl 4-Azido-5-arylthiophene-2-carboxylates

This article is focused on the development of practical approaches to the synthesis of 4-azido-5-arylthiophene-2-carboxylates and 4-amino-5-arylthiophene-2-carboxylates using the Fiesselmann reaction. The photochemical and thermal (including microwave-assisted) decomposition of 4-azido-5-arylthiophene-2-carboxylates have been studied in order to synthesize fused 4H-thieno[3,2-b]pyrrole derivatives. The proposed approaches allow to obtain functionally substituted heteroacenes, which are of interest as building blocks for organic semiconductors.

Metal-catalyzed C-S bond formation using sulfur surrogates

Sulfur-containing compounds are present in a wide range of biologically important natural products, drugs, catalysts, and ligands and they have wide applications in material chemistry. Transition metal-catalyzed C-S bond-forming reactions have successfully overcome the obstacles associated with traditional organosulfur compound syntheses such as stoichiometric use of metal-catalysts, catalyst-poisoning and harsh reaction conditions. One of the key demands in metal-catalyzed C-S bond-forming reactions is the use of an appropriate sulfur source due to its odor and availability. The unpleasant odor of many organic sulfur sources might be one of the reasons for the metal-catalyzed C-S bond-forming reactions being less explored compared to other metal-catalyzed C-heteroatom bond-forming reactions. Hence, employing an appropriate sulfur surrogate in the synthesis of organosulfur compounds in metal-catalyzed reactions is still of prime interest for chemists. This review explores the recent advances in C-S bond formation using transition metal-catalyzed cross-coupling reactions and C-H bond functionalization using diverse and commercially available sulfur surrogates. Based on the different transition metal-catalysts, this review has been divided into three major classes namely (1) palladium-catalyzed C-S bond formation, (2) copper-catalyzed C-S bond formation, and (3) other metal-catalyzed C-S bond formation. This review is further arranged based on the different sulfur surrogates. Also, this review provides an insight into the growing opportunities in the construction of complex organosulfur scaffolds covering natural product synthesis and functional materials.

The copper-catalyzed synthesis of (Z)-2H-naphtho[1,8-bc]thiophenes with solid emission

In recent years, one of the main research interests of our group has been the construction of 6/5 π-systems through the regioselective conversion of parallel alkynes in naphthalene with the aim of exploiting potential fluorescent materials. Herein, the copper-catalyzed synthesis of polysubstituted (Z)-2H-naphtho[1,8-bc]thiophenes from 8-halo-1-ethynylnaphthalenes using potassium ethylxanthate as the sulfur source is reported. In this protocol, a series of thiophene-fused 6/5 π-system compounds was synthesized via copper-catalyzed Ullmann-type C(aryl)-S bond formation and the α-addition of an alkyne bond with high selectivity and in high yields. The synthesized polysubstituted (Z)-2H-naphtho[1,8-bc]thiophenes exhibited solid emission, which made them potential candidates for use in optoelectronic conjugated materials. By using DMSO/D2O (3 : 1) as the reaction solvent, the deuterated products could be obtained in good yields under standard conditions.

Recent Progress in the Synthesis of Benzo[b]thiophene

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Due to such a wide range of applicability, the synthesis of benzo[b]thiophene derivatives has attracted intensive research. Numerous mild and efficient approaches for the synthesis of benzo[b]thiophenes have been developed over the years. Different catalysts and substrates have been applied for benzo[b]thiophene synthesis. This review will focus on the studies in the construction of benzo[b]thiophene skeleton, which date back from 2012.

CuSO4-Catalyzed dual annulation to synthesize O, S or N-containing tetracyclic heteroacenes

In this work, CuSO4 is utilized as a practical redox catalyst for tandem dual annulation in the synthesis of indole-fused tetracyclic heteroacenes, which are important skeletons in both medicinal chemistry and materials chemistry. The preparation of such skeletons in a convenient and efficient manner is in high demand. This method realizes the modular synthesis of benzofuro-, benzothieno-, and indoloindoles from abundant feedstocks such as 2-halobenzyl halides and nitrile derivatives in up to 99% yields, providing a rapid access to diverse indole-fused heteroacenes with biological or optoelectronic properties.