Palladium-Catalyzed Direct Mono- or Polyhalogenation of Benzothiadiazole Derivatives

Pd(ii)-catalyzed enantioselective C-H olefination and photoregulation of sterically hindered diarylethenes

Sterically hindered diarylethenes with intrinsic chirality have shown great potential in chiral signal regulation, light-controlled liquid crystals (LCs), etc. Their unique enantiospecific phototransformation between axial chirality of ring-open isomers and central chirality of ring-closed isomers can break through the bottleneck of interference between multiple chiral centers in traditional chiral diarylethenes. However, these intrinsic chiral diarylethenes require necessary chiral resolution through preparative chiral HPLC, typically resulting in limited separation efficiency and production scale. Here, we present an enantioselective olefination strategy to directly construct intrinsic chiral diarylethenes from a prochiral sterically hindered diarylethene, achieving high yields and enantioselectivity. The resulting isomers can be further decorated by incorporating mesogenic units, and the derivatives enable the successful reversible photoregulation of blue, green, and red reflection colors of LCs with excellent thermal stability, fatigue resistance, and little texture disorderliness, demonstrating the practical application potential of direct enantioselective olefination in photoregulation with intrinsic chiral diarylethenes.

Derivatization of 2,1,3-Benzothiadiazole via Regioselective C-H Functionalization and Aryne Reactivity

Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C-B bond, the first examples of ortho-directed C-H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.

Regioselective electrophilic aromatic borylation as a method for synthesising sterically hindered benzothiadiazole fluorophores

Regioselective stepwise phenylation of 4,7-diarylbenzo[c][1,2,5]thiadiazole fluorophores has been achieved through a facile one-pot, three-step synthetic strategy involving sequential borylation, hydroxydechlorination and Suzuki-Miyaura cross-coupling reactions. Crucial to the selectivity was the use of BCl₃ to regioselectively install a boronic acid group in the ortho-position of only one of the diaryl groups. The subsequent introduction of ortho-phenyl groups through Suzuki-Miyaura cross-coupling gave rise to twisted structures with hindered intramolecular rotation, providing a structural lever with which the fluorophore absorption and emission properties could be adjusted.

Alkali halides as nucleophilic reagent sources for N-directed palladium-catalysed ortho-C-H halogenation of s-tetrazines and other heteroaromatics

A general palladium-catalysed selective C-H halogenation reaction is reported, which was successfully achieved for a large variety of functionalized aromatic rings incorporating diverse N-directing groups. By using simple alkali halides of MX type as the nucleophilic reagent source (M = Li, Na, K, Cs and X = I, Br and Cl), and phenyliodanediacetate oxidant, clean C-H-iodination, bromination and chlorination reactions were performed. This general protocol of selective ortho-monohalogenation, which complements but contrasts with the classical methods using electrophilic reagents, is achievable in a short time (30 min) with microwave irradiation assistance. The reaction was extended to substrates bearing N-directing pyridine, pyrimidine, pyrazole, oxazoline, naphtho[1,2-d]thiazole, and azobenzene groups. Notably, the topical and selectivity-challenging s-tetrazine, as a nitrogen-rich heteroaromatic, was successfully halogenated by this protocol.

Transient Directing Group Strategy as a Unified Method for Site Selective Direct C4-H Halogenation of Indoles

A unified method for direct C4-H halogenation of indoles has been accomplished with the assistance of anthranilic acids as suitable transient directing groups. Exclusive site selectivity (one out of five potential reactive sites) as well as good functional group tolerance was obtained to install three kinds of halogen atoms (Cl, Br and I, respectively) by using inexpensive N-halosuccinimides (NXS) as halogen sources under mild conditions. Taking advantage of the rich functional groups in the product, a diversity of nitrogen-containing heterocycles were facily constructed via one-step late-stage derivations.