A Theoretical Study on the Structure of Poly((<i>R</i>)-3-hydroxybutanoic acid)

Conformational features of oligomers of 3-(R)-butanoic acid have been studied using quantum mechanics methods. Conformational search of Ac−OCH(CH3)−CH2−COOCH3 indicates that the compound is quite flexible with several conformations similar in stability. Study of Ac−[OCH(CH3)−CH2−CO]nOCH2CH3, n = 1−8, using a repeating unit approach for 21-helix, 31-helix, 41-helix, 51-helix, and pleated strand structure indicates that only the 31-helix has a cooperative effect and is also most stable. Crystal orbital calculations on the crystal packing energies of the 21-, 31-, and 41-helices have been performed. The 21-helix is found to have much stronger crystal packing stabilization than the 31- and 41-helices. This explains why the 21-helix is found in crystal structures of poly((R)-3-hydroxybutanoic acid) (PHB) despite the fact that the 31-helix is the most stable single helix. The stabilization of the 21-helix in the crystal structure is mainly from the dipole interaction between adjacent parallel helices but not from adjacent antiparallel helices. The study also provides useful information for the study of ion channel structures of PHB

Mechanistic Understanding of the Unexpected Meta Selectivity in Copper-Catalyzed Anilide C–H Bond Arylation

DFT calculations suggest that the unexpected meta product in the copper-catalyzed arylation of anilide is formed via a Heck-like four-membered-ring transition state involving a CuIII–Ph species. A competitive electrophilic substitution mechanism delivers the ortho product when a methoxy group is present at the meta position of pivanilide. A series of experiments including kinetic studies support the involvement of a CuI catalyst

Mechanistic Understanding of the Unexpected Meta Selectivity in Copper-Catalyzed Anilide C–H Bond Arylation

DFT calculations suggest that the unexpected meta product in the copper-catalyzed arylation of anilide is formed via a Heck-like four-membered-ring transition state involving a CuIII–Ph species. A competitive electrophilic substitution mechanism delivers the ortho product when a methoxy group is present at the meta position of pivanilide. A series of experiments including kinetic studies support the involvement of a CuI catalyst

Hydrogen-Bonding Directed Reversal of Enantioselectivity

A successful stereochemical reversal was achieved in AgOAc catalyzed [3+2] cycloaddition by the formation of hydrogen bonding between ligand and reactant. This strategy provides an efficient and convenient route to prepare both enantiomers of a chiral compound. DFT studies proposed a reasonable mechanism of the reversal of the enantioselectivity; hydrogen bonding changed the transition state. The strategy may provide some useful hints for ligand design

A Family of Donor–Acceptor Photovoltaic Polymers with Fused 4,7-Dithienyl-2,1,3-benzothiadiazole Units: Effect of Structural Fusion and Side Chains

A new optoelectronic building block, dithieno­[3′,2′:3,4;2″,3″:5,6]­benzo­[1,2-<i>c</i>]­[1,2,5]­thiadiazole, was designed by applying a fusion strategy on 4,7-dithienyl-2,1,3-benzothiadazole (DTBT) and named as fDTBT. In combination with benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene (BDT), fDTBT was used for the construction of a family of donor–acceptor copolymers, P­(BDT_<i>n</i>-fDTBT), with different side chains (<i>n</i> 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_<i>n</i>-fDTBT) (<i>n</i> = 8, 10, and 12) bearing small alkyl side chains show poor solubility even in hot solvents. P­(BDT_<i>n</i>-fDTBT) (<i>n</i> = 20 and 24) have good solubility but inferior photovoltaic performance with an efficiency of 1.04% and 0.49%, respectively. Only P­(BDT₁₆-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(BDT₁₆-fDTBT) with the nonfused reference polymer P­(BDT₂₀-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-C₆₁-butyric acid methyl ester (PC₆₁BM), finally resulting in improved photovoltaic performance

Highly Enantioselective Iridium-Catalyzed Hydrogenation of 2-Benzylquinolines and 2-Functionalized and 2,3-Disubstituted Quinolines

The enantioselective hydrogenation of 2-benzylquinolines and 2-functionalized and 2,3-disubstituted quinolines was developed by using the [Ir(COD)Cl]2/bisphosphine/I2 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

Highly Effective and Diastereoselective Synthesis of Axially Chiral Bis-sulfoxide Ligands via Oxidative Aryl Coupling

A series of axially chiral bis-sulfoxide ligands have been efficiently synthesized via oxidative coupling with high diastereoselectivities. The axial chirality is well controlled by the tert-butylsulfinyl or the p-tolylsulfinyl group. These axially chiral bis-sulfoxides proved to be remarkably efficient ligands for the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to 2-cyclohexenone with 99% ee

Highly Enantioselective Iridium-Catalyzed Hydrogenation of 2-Benzylquinolines and 2-Functionalized and 2,3-Disubstituted Quinolines

The enantioselective hydrogenation of 2-benzylquinolines and 2-functionalized and 2,3-disubstituted quinolines was developed by using the [Ir(COD)Cl]2/bisphosphine/I2 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

Highly Effective and Diastereoselective Synthesis of Axially Chiral Bis-sulfoxide Ligands via Oxidative Aryl Coupling

A series of axially chiral bis-sulfoxide ligands have been efficiently synthesized via oxidative coupling with high diastereoselectivities. The axial chirality is well controlled by the tert-butylsulfinyl or the p-tolylsulfinyl group. These axially chiral bis-sulfoxides proved to be remarkably efficient ligands for the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to 2-cyclohexenone with 99% ee

Chiral Rodlike Platinum Complexes, Double Helical Chains, and Potential Asymmetric Hydrogenation Ligand Based on “Linear” Building Blocks: 1,8,9,16-Tetrahydroxytetraphenylene and 1,8,9,16-Tetrakis(diphenylphosphino)tetraphenylene

This paper is concerned with the synthesis of 1,8,9,16-tetrahydroxytetraphenylene (3a) via copper(II)-mediated oxidative coupling, its resolution to optical antipodes, and its conversion to 1,8,9,16-tetrakis(diphenylphosphino)tetraphenylene (3b). On the basis of these chiral “linear” building blocks, three rodlike chiral complexes, triblock (R,R,R,R)-17 and (S,S,S,S)-20 and pentablock (R,R,R,R,R,R,R,R)-22, were constructed. As a hydrogen bond donor, racemic and optically active 3a was allowed to assemble with linear acceptors to afford highly ordered structures. A 1:1 adduct of 4,4‘-bipyridyl and (±)-3a exists in a dimeric form of 3a linked by 4,4‘-bipyridyl through hydrogen bonds. Pyrazine serves as a short linker between achiral parallel chains each formed by (±)-3a, while self-assembly of homochiral 3a into alternate parallel chains occurs in the adduct of 5,5‘-dipyrimidine with (±)-3a. Self-assembly of (S,S)-3a or (R,R)-3a with 4,4‘-dipyridyl yielded a packing of chiral double helical chains formed by chiral tetrol 3a molecules. A novel chiral ligand, (S,S)-23, derived from 3a was used in the asymmetric catalytic hydrogenation of α-acetamidocinnamate, yielding up to 99.0% ee and 100% conversion