Synlett

This SYNLETT cluster highlights research work conducted in universities across Thailand. As a country rich in biodiversity, chemical research in Thailand was originally founded on the study of natural products. The discovery and development of novel, biologically active agents has contributed to drug discovery and advanced the development of novel compounds.1 Since the 1990s, the growth of petrochemical industries in Southeast Asia has spurred chemical research on synthetic methodologies, the creation of high-value compounds from petroleum-based starting materials and polymer sciences. The results have led to significant economic and strategic advantages that have enabled the competitiveness of local petrochemical industries. Moving into the new era, Thailand and the region faces global sustainability challenges. Green chemistry has also become a key theme for driving chemical research, which is expected to help in generating new ideas and innovations to deliver a more sustainable society. This cluster contains 27 articles that have been submitted from 12 different Thai universities. The articles are organized into 3 main themes, as outlined below.

Synlett 2022; 33: V-DOI: 10.1055/s-0041-1738690Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

This article aims to summarizing the evolution of my lab’s research efforts in making and understanding peptide macrocycles. What started as a curiosity-driven investigation of amphoteric structures in multicomponent reactions, has turned into a sustained exploration of complex macrocyclic peptides. As part of this journey, my students and I have introduced new tools that enable chemical synthesis and property-driven optimization of cyclic peptides. These contributions are expected to be relevant in the areas of drug discovery and biological probe design.

Catalytic asymmetric 1,3-dipolar cycloaddition reactions of activated isocyanides with various 2π dipolarophiles have been intensively studied, affording a wide range of enantioenriched five-membered N-heterocycles. In sharp contrast, the catalytic enantioselective higher-order cycloaddition of activated isocyanides has not been achieved yet. We present here our recent work on the development of an unprecedented silver-catalyzed highly diastereo- and enantioselective [3+3] cycloaddition of activated isocyanides with azomethine imines. This method features high efficiency, good to excellent stereocontrol, wide substrate scope, as well as operational simplicity. It is also noteworthy that the same catalytic system was proved to be suitable for not only the late-stage functionalization of complex bioactive molecules but also the kinetic resolution of racemic azomethine imines.1 Introduction2 Results and Discussion3 Summary and Outlook

A tandem formal [3+3]-cycloaddition/oxidation between chalcones and β-enamine esters, employing iodine as a catalyst, was developed for the construction of various substituted m-terphenyls. A wide range of chalcones and β-enamine esters were tested under metal- and solvent-free conditions for the synthesis of substituted m-terphenyls in good to excellent yields in the presence of sulfur as an oxidant. This reaction proceeds with the formation of four new bonds and one new ring, with a high atom economy.

In recent years, gold catalysis involving Au(I)/Au(III) redox cycle has gained significant attention. This account summarizes our contributions to the development of Au(I)/Au(III) catalysis, focusing on cross-coupling reactions and 1,2-difunctionalization reactions of C–C multiple bonds. A special emphasis has been given to understanding the mechanism of the reactions.1 Introduction2 Gold-Catalyzed Cross-Coupling Reactions3 Gold-Catalyzed 1,2-Difunctionalization of C–C Multiple Bonds4 Conclusion and Outlook

The synthesis of 2-C-substituted 5-deoxyglucals from d-ribose, by using a nickel-catalyzed cross-coupling reaction of 2-iodo-5-deoxyglucals with Grignard reagents, is reported. The obtained 2-C-substituted 5-deoxyglucals were then transformed into 2-C-substituted 5-deoxyglycosides and 2-C-substituted 5-deoxynucleosides. During this work, structures published in the literature were reassigned.

Photochemical cascade (domino) reactions provide a unique opportunity for the construction of complex molecular architectures. Specifically, an intramolecular ortho photocycloaddition of 7-(alkenyloxy)-indanones triggers a sequence of consecutive reactions that can lead in a single operation to the complete skeleton of two important classes of sesquiterpenes: protoilludanes and prezizaenes. In the former case, two transformations follow the initial photocycloaddition, while in the latter case, there are three consecutive transformations, two of which are initiated by a photon. Remarkably, the reaction cascades proceed with exquisite diastereoselectivity, generating three (protoilludane) or five (prezizaene) stereogenic centers with defined relative configurations.1 Introduction2 First Encounter and Initial Studies3 Protoilludane-Type Sesquiterpenes4 Prezizaene-Type Sesquiterpenes5 Enantioselectivity6 Perspective and Summary

Controlled sulfonyl migration is considered an important transformation for total synthesis and scaffold elaboration. Accordingly, efforts to understand the underlying properties of these often serendipitously identified reactions have important implications. Following the attempted synthesis of a tetrahydroindazolone analogue, we report here an unexpected 1,5-nitrogen to carbon tosyl migration, resulting in the isolation of an unusual sulfonated dimedone. Synthetic and mechanistic investigations provide early insight into the scope of this reaction, with two potential mechanisms proposed.

The strained/frustrated electrostatic interactions between the ion pair of TTBPy+X– increases the reactivity in both the ions, resulting in the activation of a third molecule like sulfonamides (aromatic/­aliphatic) via hydrogen bonding. This intriguing weak-interactions-based reactivity has been utilized to develop an organocatalytic synthesis of 2-deoxy-sulfonamido-glycosides from glycals. The sulfonamidoglycosylation of glycals using a catalytic amount of 2,4,6-tri-tert-butylpyridinium salts proceeded stereoselectively to provide N-glycosides in good to high yields. This process was demonstrated with l-rhamnal and d-galactal. Besides, IR spectroscopic studies explain that the hindered protonated pyridine cannot behave as a cationic Brønsted acid as is generally perceived.