Synthesis of Difluoroglycine Derivatives from Amines,Difluorocarbene, and CO2: Computational Design,Scope, and Applications

A three-component reaction (3CR) for the synthesis of difluoroglycine derivatives has been achieved by using amines, difluorocarbene (generated in situ), and the abundant, inexpensive, and nontoxic C₁ source CO₂. Various tert-amines and pyridine, (iso)quinoline, imidazole, thiazole, and pyrazole derivatives were incorporated, and the corresponding products were isolated in solid form without purification by column chromatography on silica gel. Detailed reaction profiles of the 3CR were obtained from computational analysis using DFT calculations, and the results critically suggest that simple ammonia is not applicable to this reaction. In addition, as strongly supported by computational predictions, a new reagent that can generate difluorocarbene at 0 °C without any additives was discovered. Finally, radical substitution reactions of the obtained difluoroglycine derivatives under photoredox conditions, as well as a synthetic application as an N-heterocyclic carbene ligand are shown.     

ABC–ABC-Type Directly meso–meso Linked Porphyrin Dimers

Covalently linked porphyrin oligomers are attractive because of their extended π-conjugated systems. Among various porphyrin oligomers, directly meso–meso linked porphyrin oligomers exhibit unique photophysical properties due to their strong exciton couplings derived from the alternative orthogonal geometry of the porphyrins. Although their structural and electronic properties can be greatly altered by substituents at meso positions, it is still difficult to introduce different substituents at the meso positions. Thus, it is a challenge to develop general synthetic methodologies for functional porphyrin dimers and oligomers with different substituents at the meso positions. Herein, a general synthetic strategy for ABC–ABC-type directly meso–meso linked porphyrin dimers by stepwise functionalization starting from 10,15,20-meso-free 5-substituted porphyrin as building block is established. A meso-ABC–ABC-type meso–meso-linked donor–π-acceptor-type porphyrin dimer was prepared and exhibited the highest power conversion efficiency (7.91 %) ever reported for dye-sensitized solar cells based on dimeric orthogonal donor–π-acceptor-type organic sensitizers. This synthetic strategy will provide useful guidance for the rational design of functional porphyrin dimers and oligomers for diverse applications.     

Phenolic Compounds Isolated from the Bark of Abies sachalinensis

Eight spiro‐biflavonoids named abiesinols A–H, along with three neolignans, quercetin, and protocatechuic acid were isolated from the MeOH extract of the bark of Abies sachalinensis. The structures of these phenolic compounds were characterized by spectroscopic methods including NMR and MS. The absolute configurations of the abiesinols were determined by Mosher's method, CD, and NOESY data.     

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l ‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d ,l ‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T_g = approximately ?40 °C). Successive polymerization of l ‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (T_m = approximately 150 °C) for the crystalline PLLA segments and still low T_g (approximately ?30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their T_m as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 489–495