A new optoelectronic building block, dithieno-[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole, was designed by applying a fusion strategy on 4,7-dithienyl-2,1,3benzothiadazole (DTBT) and named as fDTBT. In combination with benzo[1,2-b:4,5-b′]dithiophene (BDT), fDTBT was used for the construction of a family of donor−acceptor copolymers, P(BDT n -fDTBT), with different side chains (n is carbon number of the side chain and varies from 8, 10, 12, 16, 20, to 24). It was found that the side chains have great impact on processing and photovoltaic properties of the polymers. P(BDT n -fDTBT) (n = 8, 10, and 12) bearing small alkyl side chains show poor solubility even in hot solvents. P(BDT n -fDTBT) (n = 20 and 24) have good solubility but inferior photovoltaic performance with an efficiency of 1.04% and 0.49%, respectively. Only P(BDT 16 -fDTBT) having 2-hexyldecyl side chain possesses both suitable solution processability and good photovoltaic properties with an efficiency around 4.36%. The comparison between P(BDT 16 -fDTBT) with the nonfused reference polymer P(BDT 20 -DTBT) reveals that the structural fusion on DTBT endows the polymer a deeper HOMO energy level and a better film morphology when blending with [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM), finally resulting in improved photovoltaic performance.

The enantioselective hydrogenation of 2-benzylquinolines and 2-functionalized and 2,3-disubstituted quinolines was developed by using the [Ir(COD)Cl](2)/bisphosphine/I(2) system with up to 96% ee. Moreover, mechanistic studies revealed the hydrogenation mechanism of quinoline involves a 1,4-hydride addition, isomerization, and 1,2-hydride addition, and the catalytic active species may be a Ir(III) complex with chloride and iodide.

The preparation of both enantiomers of a chiral compound is still a vital task in pharmaceutical and bioorganic chemistry. 1 Basically, it can be achieved with the use of both enantiomers of a chiral ligand, respectively, in a catalytic asymmetric process. However, the two enantiomers of a chiral ligand are not always easily available from natural chiral sources, such as amino acids, carbohydrates, and alkaloids. Alternatively, the enantioselectivity can be reversed by using different metals 2 in the presence of the same ligands, including additives, 3 or changing the reaction parameters (temperature 4 and solvents 5 ) or other methods. 6 Although the use of hydrogen bonding to accelerate or catalyze certain reactions has been well documented recently, 7 reversal of enantioselectivity directed by hydrogen bonding is still rare. 8 We envisage that the formation of hydrogen bonds may reverse the enantioselectivity if ligands were properly designed. The reversal could be caused by the variation of reaction transition states (Figure 1), in which transition state A is common. Both substrates SM1 and SM2 coordinate with the central metal M, but in transition state B, SM2 can coordinate with the central metal M, while the other substrate SM1 has an interaction with NH 2 of the ligand through hydrogen bonding. Thus, different enantiofacial attack was afforded, leading to the reversal of enantioselectivity. In this Communication, we present a hydrogen-bond-directed reversal of enantioselectivity in AgOAc-catalyzed [3+2] cycloaddition of azomethine ylides.In our initial study, we chose the cycloaddition of iminoester 2a with dimethyl maleate as the model reaction, which is a useful way to form highly substituted pyrrolidine rings 9 (Table 1). Ligands 1a-e could be conveniently synthesized according to the known literature method. 10 The reaction proceeded smoothly in the presence of AgOAc/1a in Et 2 O, and only endo cycloaddition product was detected with 76% ee. To our delight, the opposite absolute configuration of adduct 3a was obtained with 83% ee when ligand 1b was used, whose substituents on the N atom are H atoms. To achieve better enantioselectivity, we replaced phenyl groups in 1a/ 1b with 3,5-dimethylphenyl (1c/1d). Both enantiomers of adduct 3a were obtained with 84% and -84% ees, respectively (entries 3 and 4). The ee was improved to 92% using 1c when the reaction was run at -25°C. Adduct 3a with 92% ee and opposite absolute configuration was obtained using ligand 1d at -25°C. Thus, both enantiomers of adduct 3a can be obtained with excellent enantioselectivity using AgOAc/1c/-25°C and AgOAc/1d/-25°C, respectively.To explore the scope of the hydrogen bond-directed reversal of enantioselectivity in cycloaddition of azomethine ylides, a variety of iminoester substrates derived from aldehydes with different steric and electronic properties were examined (Table 2). All reactions went to completion within 4 h in high isolated yields (91-98%). Reversal of the absolute configuration was realized in the reactions...

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Two chiral tetraphenylenes, 2,15-dideuteriotetraphenylene (7) and 2,7-dimethyltetraphenylene (15) were synthesized and resolved to address the tetraphenylene inversion barrier problem. Neutron diffraction investigation of enantiopure 7 showed that the molecule retained its chirality integrity during its synthesis from enantiopure precursors and therefore rules out the possibility of the tetraphenylene framework possessing a low-energy barrier to inversion. Thermal study on 15 and tetraphenylene 1 further revealed that their inversion barriers were not overcome up to 600 degrees C, at which temperature these compounds underwent skeletal contraction into triphenylene with activation energies of 62.8 and 58.2 kcal/mol, respectively. This result is supported by computational studies which yielded an inversion barrier of 135 kcal/mol for tetraphenylene as a consequence of the peri-hydrogen repulsions at its planar conformation.

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Cyclic ketones react with (E)-2-nitroallylic acetates in the presence of catalytic pyrrolidine-thiourea, which affords bicyclic skeletons with four or five stereocenters in one single reaction with up to 98 % ee in moderate to high yields. The cooperative effects of both enamine and the Brønsted acid are found to be crucial for the high reactivity and enantioselectivity of this cascade reaction, which is demonstrated by both theoretical calculation and experimental data.

ABSTRACT:The Rh(I)-catalyzed direct reorganization of organic frameworks and group exchanges between carboxylic acids and aryl ketones was developed with the assistance of directing group. Biaryls, alkenylarenes, and alkylarenes were produced in high efficiency from aryl ketones and the corresponding carboxylic acids by releasing the other molecule of carboxylic acids and carbon monoxide. A wide range of functional groups were well compatible. The exchanges between two partners were proposed to take place on the Rh-(III) center of key intermediates, supported by experimental mechanistic studies and computational calculations. The transformation unveiled the new catalytic pathway of the group transfer of two organic molecules. ■ INTRODUCTIONTraditional organic synthesis basically depends on the transformations between different functional groups. The scaffold reorganization of organic compounds through C−C bond cleavage could be a conceptually different, straightforward and efficient strategy to build up new skeletons from existing structural units. 1 Transition-metal catalyzed selective C−C bond activation (cleavage) is currently of great interest to organometallic chemists, due to not only its fundamental academic interest to carry out the reorganization of organic molecule skeletons, but also its potential application in organic synthesis. 2 However, the cleavage of C−C bonds faces several challenges from both thermodynamic and kinetic issues, including high bond dissociation energy (BDE) of C−C bonds while relatively lower BDE of forming C−M bonds, steric hindrance of attacked C−C bonds, and selectivity among various C−C bonds in the same molecule. 3 Over the past few decades, significant progress has been made to cleave C−C bonds through different strategies, for example, by relieving the strain of small rings, 4 forming small molecules, 5 inducing aromatic stabilization, 6 forming stable metallacyclic complexes, 7 cleavage of C−CN bond 8 and others. 9 Another successful strategy is to use directing group to assist the C−C cleavage, as shown in pioneer works by Suggs, 10 Jun 2c,e,11 and others. 12 With this strategy, our group recently reported the Rh-catalyzed selective cleavage of C−C bonds of secondary benzyl alcohols and following transformations. 5f,h,12e Among many types of organic molecules, ketones were seriously regarded as an objective due to their unique reactivity in the field of C−C activation (Figure 1). 4e,h,k,p,q,7b,9b,c,f,j−l,12h For example, with directing strategy in the presence of Rh(I), either one of the acyl C−C bond was cleaved through oxidative addition (path a and path b in Figure 1). Through path a, the carbonyl group remained, and new C−C bonds were formed