Synlett

Herein we report the synthesis of nonsymmetrically substituted azobenzene derivatives with meta-alkyl substituents on one side and meta-aryl moieties with electron-donating or electron-withdrawing groups on the other side. The half-lives for the thermal (Z)- to (E)-isomerization of these molecules were measured in n-octane, which allows investigation of the strength of the aryl–alkyl interactions between their substituents. It was found that the London dispersion donor strength of the alkyl substrate is the decisive factor in the observed stabilization, whereas the electronic structure of the aryl fragment does not influence the isomerization in a significant way.

A computational study of the aza-Cope rearrangement leading to angularly substituted 1-azabicyclic ring systems is presented. The calculations estimate the probability of the proton transfer between reaction intermediates and protic solvents, explain the experimentally observed reaction selectivity, and suggest new potentially more efficient systems for further in vitro and in silico investigations.

A metal-free approach for C(sp3)–H activation followed by an intramolecular Giese reaction to construct a wide range of cyclic ether scaffolds of various ring sizes under environmentally benign and straightforward conditions is reported. An easily prepared pyrylium salt is employed as an organophotocatalyst for this visible-light-driven, highly atom-economical (PMI = 64.34 g/g for a 0.2 mmol scale), cost-effective, and chemoselective transformation. The reported method has a broad functional-group tolerance, resulting in good-quality products. Furthermore, downstream functionalizations of a product and a gram-scale synthesis (PMI = 17.41 g/g for a 10 mmol scale) are demonstrated, highlighting our method’s advantages.

Synlett 2022; 33: A167-A182DOI: 10.1055/s-0040-1720577Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

Synlett 2022; 33: V-DOI: 10.1055/s-0042-1752367Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

Zhipeng Zhang (left) received his B.S. degree from Shandong University (China) in 2004, and his Ph.D. degree from the Shanghai Institute of Organic Chemistry (SIOC) in 2010 under the supervision of Professor Kuiling Ding. In 2011, he began his postdoctoral studies with Professor Benjamin List at the Max Planck Institute for Coal Research in Mülheim an der Ruhr, Germany. After three years of research on asymmetric organocatalysis, he joined the group of Professor Jin-Quan Yu at The Scripps Research Institute in La Jolla, California as a postdoctoral research associate in 2014. He subsequently worked at the Genomics Institute of the Novartis Research Foundation (GNF) from 2016, before he began his independent career as a professor at the East China University of Science and Technology (ECUST) in 2017. His current research interests include asymmetric catalysis and synthetic methodology, focusing on the design and development of novel chiral ligands and catalysts.
Baoguo Zhao (right) received his B.S. degree from Wuhan University in 1996, his M.S. degree from Nanjing University under the supervision of Professor Jianhua Xu in 2002, and his Ph.D. degree from the Shanghai Institute of Organic Chemistry (SIOC) under the supervision of Professor Kuiling Ding in 2006. He subsequently worked with Professor Yian Shi for five years as a postdoctoral fellow at the Department of Chemistry of Colorado State University. In 2011, he joined Shanghai Normal University at the Department of Chemistry as a full professor. His current research interests are in the area of biomimetic asymmetric catalysis, including the development of bioinspired chiral catalysts and synthetic methodologies.

Vicinal dihalides not only emerge as reactive intermediates in synthetic organic chemistry, but also are extensively existing in bioactive marine natural products. The dihalogenation of alkenes is the most direct and effective method for the synthesis of vicinal dihalides. Because there is always an exchange process between the chiral haloniums and the unreacted olefins to cause racemization, the development of catalytic enantioselective dihalogenation of alkenes is of great difficulty. Recently, great progress has been made in catalytic asymmetric manner. However, there is a lack of related review of discussions of the mechanisms and reaction systems. This review is aimed at summarizing enantioselective dihalogenation of alkenes, including 1,2-dichlorination, 1,2-dibromination, and 1,2-difluorination, which is expected to encourage more researchers to participate in this field.1 Introduction2 Enantioselective 1,2-Dichlorination and 1,2-Dibromination of Alkenes2.1 Chiral-Boron-Complex-Promoted Enantioselective 1,2-Dichlorination2.2 Organocatalytic Asymmetric 1,2-Dichlorination and 1,2-Dibromination2.3 Chiral-Titanium-Complex-Catalyzed 1,2-Dihalogenation3 Chiral-Iodide-Catalyzed Enantioselective Oxidative 1,2-Difluorination4 Summary and Outlook

A visible-light-induced O–H insertion reaction of diazo compounds is reported. This synthetic method, unlike conventional pathways, does not rely on transition metals, Lewis acids, or Brønsted acids; does not use any catalyst; and produces valuable α-hydroxy and α-alkoxy esters in good yields of up to 98%. The protocol exhibits a broad substrate scope and good functional-group tolerance. Notably, a gram-scale synthesis has been performed in a photochemical continuous-flow mode.

Ni(II) complex of the Schiff base of the chiral auxiliary (S)-2-N-(N′-benzylprolyl)aminobenzophenone (BPB) and dehydroalanine as the initial complex in the addition reaction was investigated. The obtained four new derivatives of α-alanine were investigated as inhibitors of aldose reductase. Only one of them: (S)-2-amino-3-[(4-methylbenzyl)amino]propanoic acid showed activity. It becomes a reason for studying the patterns of biological activity of the structure of α-amino acids. The results of docking analysis indicated that (S)-2-amino-3-[(4-methylbenzyl)amino]propanoic acid demonstrated the ability to form bonds with different functional groups of the enzyme which let us assume that some amino acids of nonfunctional groups, such as Trp20 of ALR2, can play a key role in inhibitor–enzyme interactions.

A chiral ruthenium catalyst is introduced which contains a cyclometalated N-(3-nitrophenyl)-imidazo[1,5-a]pyridinylidene ligand in addition to a bidentate 4-mesityl-2-(pyridin-2-yl)thiazole and two acetonitriles to complement the octahedral coordination sphere of the monocationic complex. Tetrafluoroborate serves as the counterion. Since all coordinated ligands are achiral, the overall chirality is formally due to a stereogenic metal center generating either a left-handed (Λ) or right-handed (Δ) helical topology of this chiral-at-metal complex. Nonracemic Λ and Δ complexes were synthesized using (R)- and (S)-N-benzoyl-tert-butanesulfinamide as chiral auxiliary ligands, respectively. The position of the nitro group in the metalated phenyl moiety is of crucial importance for the generation of enantiomerically pure complexes. The catalytic activity of the cycloruthenated chiral-at-metal catalyst was demonstrated for the enantioselective intramolecular cyclopropanation of trans-cinnamyl diazoacetate and an alkenyl diazoketone to generate bicyclic cyclopropanes in high yields (96–97%) and with satisfactory enantioselectivity (93% ee).