Novel Aliphatic Polyesters Based on Functional Cyclic (Di)Esters

Recent progress in the chemical synthesis of novel aliphatic polyesters via ring‐opening polymerization of functional cyclic (di)esters are reviewed in this article. Syntheses of these functional aliphatic polyesters are being classified into three groups according to the structure of the cyclic monomers: (i) cyclic diesters, (ii) morpholine‐2,5‐dione derivatives, and (iii) cyclic esters. Progress in the synthesis and polymerization of monomers in each category is reported with an emphasis on controlled synthesis. The recent achievements have enabled the synthesis of a variety of novel aliphatic polyesters, including hydrophilic, halogenated, and unsaturated polyesters.

Structure of the most common R‐functionalized cyclic precursors of aliphatic polyesters.     

Vector-valued singular integral operators with rough kernels

In this paper, we establish a weak-type (1,1) boundedness criterion for vector-valued singular integral operators with rough kernels. As applications, we obtain weak-type (1,1) bounds for the convolution singular integral operator taking value in the Banach space Y with a rough kernel, the maximal operator taking vector value in Y with a rough kernel and several square functions with rough kernels. Here, $Y={[H,X]}_{\theta }$ is a complex interpolation space between a Hilbert space H and a UMD space X.     

Circumcoronenes

Circumcoronene, a hexagonal graphene fragment with six zigzag edges, has been the focus of theoretical studies for many years, but its synthesis in solution has remained a challenge. In this study, we present a facile method for synthesizing three derivatives of circumcoronene using Brønsted/Lewis acid-mediated cyclization of vinyl ether or alkyne. Their structures were confirmed through X-ray crystallographic analysis. Bond length analysis, NMR measurement, and theoretical calculations showed that circumcoronene mostly follows Clar's bonding model and exhibits dominant local aromaticity. Its absorption and emission spectra are similar to those of the smaller hexagonal coronene due to its six-fold symmetry.     

A Fused [5]Helicene Dimer with a Figure-Eight Topology: Synthesis,Chiral Resolution,and Electronic Properties

Chiral shape-persistent molecular nanocarbons are promising chiroptical materials; their synthesis, however, remains a big challenge. Herein, we report the facile synthesis and chiral resolution of a double-stranded figure-eight carbon nanobelt 1 in which two [5]helicene units are fused together. Two synthetic routes were developed, and, in particular, a strategy involving Suzuki coupling-mediated macrocyclization followed by Bi(OTf)₃-catalyzed cyclization of vinyl ether turned out to be the most efficient. The structure of 1 was confirmed by X-ray crystallographic analysis. The isolated (P,P)- and (M,M)- enantiomers show persistent chiroptical properties with relatively large dissymmetric factors (|g_abs|=5.4×10⁻³ and |g_lum|=1.0×10⁻²), which can be explained by the effective electron delocalization along the fully conjugated belt and the unique D₂ symmetry. 1 exhibits local aromatic character with a dominant structure containing eight Clar's aromatic sextet rings.