Fjord-Type AIEgens Based on Inherent Through-Space Conjugation

Through-space conjugation(TSC)is a noncovalently electronic interaction that is emerging as a potential complement to through-bond conjugation(TBC)-based strategies for constructing luminescent materials.However,the design of efficient luminogens based on TSC is currently challenging due to a lack of established structure-property understanding.This is particularly true in the case of luminogens displaying aggregation-induced emission(AIE)effects.In this work,three terphenyl derivatives were prepared,and their photophysical properties were systemically studied.It was found that relative to the corresponding m-and p-linked analogues,the electronic interaction of TBC is weakened while the strength of TSC is commensurately enhanced in the constitutional isomer containing an o-linked fjordtype subunit.Within this set of luminogens,the presence of a fjord-type arrangement promotes a transformation from aggregation-caused quenching to AIE.Further investigations involving congeneric quaterphenyl and pentphenyl isomers support the universality of the fjord-type unit as a framework for synthesizing AIE-active luminogens(AIEgens)with inherent TSC.This work not only provides a novel set of AIEgens but also establishes the utility of TSC in controlling the photophysical properties of nonconventional and twisted luminogens.

Synthesis of Chiral β-Lactams by Pd-Catalyzed Enantioselective Amidation of Methylene C(sp3)-H Bonds

A Pd(Ⅱ)-catalyzed enantioselective intramolecular amidation of both benzylic and unbiased methylene C(sp^3)-H bonds for the straightforward synthesis of chiral B-lactams from aliphatic carboxamides is reported.The combination of 2 prinylisopropyl(PIP)auxiiary with 3,3′-subtituted BINOL ligands is crucial for the enhancement of both reactivity and enantiocontrol of differentiating unbiased meth-ylene C(sp^3)-H bonds.The desired chemoselective C-N reductive elimination was achieved by employing 2-fluoro-1-iodo-4-nitrobenzene as oxidant.

Synthesis of Chiral β-Lactams by Pd-Catalyzed Enantioselective Amidation of Methylene C(sp3)-H Bonds Enabled by a 2-Pyridylisopropyl Auxiliary

In recent years,enantioselective C-H functionalization reactions have emerged as an efficient means to construct complicated chiral molecules.Compared to many precedents on the asymmetric functionalization of aryl C-H bonds,enantioselective functionalization of unbiased methylene C(sp3)-H bonds of linear systems via metal insertion is still very challenging for two main reasons(Scheme 1a).[1]First,it is more difficult to differentiate two enantiotopic protons residing on a single carbon center.Second,unbiased methylene C(sp3)-H bonds are less reactive than those of primary methyl and activated by specific electronic or inductive effects,such as C-H bonds adjacent to N-heteroatom,benzylic position or on conformationally rigid cyclic systems.The major breakthrough was first achieved by the Yu group in 2016(Scheme 1b).They developed a Pd(Ⅱ)-catalyzed arylation of unbiased methylene C(sp3)-H bonds in high enantioselectivity by taking advantage of weakly coordinating monodentate DG with a bidentate acetyl-protected aminoethyl quinolone ligand(up to 96%ee).