Dehydrohalogenative polycondensation of 2-bromo-3-hexylthiophene was successful with Herrmann's catalyst and tris(2-dimethylaminophenyl)phosphine as catalyst precursors, giving head-to-tail poly(3-hexylthiophene) (HT-P3HT) with high molecular weight (M(n) = 30,600, M(w)/M(n) = 1.60) and high regioregularity (98%) in almost quantitative yield (99%).

The palladium-catalyzed direct arylation of aromatic compounds with aryl halides has been proposed to involve an arylpalladium carboxylate intermediate. However, isolated arylpalladium complexes, which undergo C−H bond cleavage of aromatic substrates without the aid of additional activators or promoters, have been scarcely documented. This paper reports that [PdAr(μ-O 2 CR)(PPh 3 )] n complexes (1: Ar = Ph, 2-MeC 6 H 4 , 2,6-Me 2 C 6 H 3 ; R = Me, t Bu) successfully react with 2-methylthiophene (2) in the absence of additives to afford 5-aryl-2-methylthiophenes (3) in high yields. The reactivity increases with increasing bulkiness of the Ar group, whereas the bulky pivalate ligand (R = t Bu) reduces the reactivity as compared with the acetate ligand (R = Me). Complex 1 is in equilibrium with the monomeric species [PdAr(O 2 CR-κ 2 O)(PPh 3 )] (5) in solution, as confirmed by IR spectroscopy. Kinetic examinations have suggested that the direct arylation proceeds via 5, which undergoes C−H bond cleavage of 2. Complex 1 serves as a good catalyst for direct arylation of 2 with aryl bromides.

The synthesis of regioregular head-to-tail poly(3-hexylthiophene)s capped with aryl groups (Ar-HT-P3HTs) has been accomplished by palladium-catalyzed polycondensation of 2-bromo-3-hexylthiophene (1) via direct arylation. A variety of aryl groups are installed at the initiated end in 86%-98% selectivity using aryl bromides and iodides as capping agents. The polymerization proceeds via a two-stage process. Before monomer 1 is consumed, the competitive formation of end-capped and non-capped HT-P3HTs is operative, where the molecular weight increases linearly with monomer conversion. After 1 is consumed, the resulting polymers are coupled with each other to afford highly end-capped HT-P3HTs.

Diethanolamine (DEA) has been extensively utilized as an alkaline buffer in current assays of alkaline phosphatase (ALP) activity in the past decades. While playing the role of a buffer, the chemical reactivity of DEA has been widely ignored in such assays. Herein, we report an interesting chromogenic interaction between DEA and 4-aminophenol (AP) in the presence of HO for the first time, which inspires us to develop a novel DEA-participated ALP activity assay by using 4-aminophenyl phosphate (APP) as a substrate. This APP/DEA-based colorimetric approach has been proved to be comparable and even superior to the conventional p-nitrophenyl phosphate (pNPP)-based one, especially in the low ALP activity region, due to its higher sensitivity. The clear response mechanism and excellent sensing performance ensure that it can be further applied to determining ALP activity in real biological samples, screening potential ALP inhibitors in vitro, establishing ALP-enabled ELISA, and even fluorophore-assisted fluorescent ALP activity assay. It is demonstrated that this strategy not only possesses a good feasibility, but also exhibits a promising outlook for a series of ALP-related and -extended detections.

No abstract

An unprecedented approach for the synthesis of imine derivatives was achieved via a Pd(II)-catalyzed dearomatization reaction of N-aryl ureas with internal alkynes. The corresponding spirocyclic imine derivatives were obtained with 20 examples in good to excellent yields. Mechanistic investigation indicated that an interesting 1,3-palladium migration process led to the α-regioselective dearomatization when 2-naphthyl ureas were used as the substrates. Fused ring products could also be obtained to further prove this migration process.

Analyte-responsive chromo-fluorogenic reactions under accessible conditions are important for designing small-molecule spectroscopic probes. We describe a series of newly constructed motifs based on the chromo-fluorogenic reaction between catechol derivatives (typically hydroxytyrosol, dopamine, and levodopa) and naphthoresorcin (NR) in aqueous solution under ambient conditions. The weakly absorptive and fluorogenic catechols/NR was converted to products having visible absorption and bright fluorescence within several minutes. The chromo-fluorophores produced from this reaction had a maximum absorbance at 458 nm and emission at 480 nm with high fluorescence quantum yields (30–84%). Inspired by the tyrosinase-catalyzed hydroxylation of monophenols to catechols, the tyrosinase-enabled chromo-fluorogenic reaction was verified by using monophenol (typically tyrosol) as the substrate. In this regard, a dual-readout tyrosinase activity assay was developed by virtue of the in situ “turn-on” optical signals. Furthermore, a test of tyrosinase inhibition, by using a common inhibitor kojic acid, demonstrated the potential of the chromo-fluorogenic reaction for developing other tyrosinase related assays and signal transduction.

This paper reports a conceptually new and concise synthetic method leading to unprecedented, fully alkyl substituted pyranylidene carbene complexes 2 from M(CO) 6 (M ) Cr, Mo, W) and the readily aVailable 1-lithio-1,3-butadiene 1, bearing a leaVing group, Via an intramolecular trapping of metallaacylate intermediates. These carbenes haVe been demonstrated to haVe interesting and unique reactiVity.Synthesis and demetalation of Fischer-type carbene complexes have continuously been a challenging subject in synthetic science and chemical industry. 1 Among the family of Fischertype carbene complexes, six-membered pyranylidene carbene complexes of the group 6 metals Cr, Mo, and W have recently attracted increasing interest due to their utilizations in ringopening reactions, 2 Diels-Alder reactions, 3 and 1,6-addition. 4 Several methods have been developed for the syntheses of pyranylidene carbene complexes; 5-8 the first report was by the reaction of cyclopropenylidene complexes with pyridinium ylides. 5 The condensation reactions of the (1-alkynyl)carbene complexes (CO) 5 MdC(OEt)CtCPh (M ) Cr, W) with carbon nucleophiles, e.g. 1,3-diketones, provided a typical route for the formation of pyranylidene carbene complexes, which bear one acyl group and two alkyl/aryl groups on the pyran ring. 6 Recently, two independent groups, Iwasawa 3b,c,4 and Uemura, 7 have reported the reaction of M(CO) 5 • L (M ) Cr, Mo, W; L ) THF, NEt 3 ) with β-ethynyl R,β-unsaturated