5-Endo-dig cyclizations in organic syntheses

Design and Synthesis of Indazole-Indole Hybrid via tert-Butyl Nitrite Mediated Cascade Diazotization/Isomerization/Cyclization

In this report, a tert-butyl nitrite (TBN)-mediated straightforward metal-free approach has been presented for the synthesis of a diverse range of C-3-substituted indazole-indole hybrids using readily accessible 2-(indolin-3-ylidenemethyl)aniline derivatives. This strategy is proposed to occur via a diazonium salt intermediate that is capable of cascade isomerization and intramolecular C-N bond formation through a 5-endo-dig cyclization to achieve a wide variety of indazole-indole hybrids in good yields.

Selenium in Peptide Chemistry

In recent years, researchers have been exploring the potential of incorporating selenium into peptides, as this element possesses unique properties that can enhance the reactivity of these compounds. Selenium is a non-metallic element that has a similar electronic configuration to sulfur. However, due to its larger atomic size and lower electronegativity, it is more nucleophilic than sulfur. This property makes selenium more reactive toward electrophiles. One of the most significant differences between selenium and sulfur is the dissociation of the Se-H bond. The Se-H bond is more easily dissociated than the S-H bond, leading to higher acidity of selenocysteine (Sec) compared to cysteine (Cys). This difference in acidity can be exploited to selectively modify the reactivity of peptides containing Sec. Furthermore, Se-H bonds in selenium-containing peptides are more susceptible to oxidation than their sulfur analogs. This property can be used to selectively modify the peptides by introducing new functional groups, such as disulfide bonds, which are important for protein folding and stability. These unique properties of selenium-containing peptides have found numerous applications in the field of chemical biology. For instance, selenium-containing peptides have been used in native chemical ligation (NCL). In addition, the reactivity of Sec can be harnessed to create cyclic and stapled peptides. Other chemical modifications, such as oxidation, reduction, and photochemical reactions, have also been applied to selenium-containing peptides to create novel molecules with unique biological properties.

A Pd-catalyzed one-pot cascade consisting of C-C/C-O/N-N bond formation to access benzoxazine fused 1,2,3-triazoles

A Pd-catalyzed one-pot cascade consisting of C-C/C-O/N-N bond formation to access clinically important fused 1,2,3-triazoles using N-aryl-α-(tosylhydrazone)acetamides with isocyanide has been developed. Besides, various substitutions on the N-aryl part of acetamides along with different isocyanides show good compatibility in this protocol. Next, two plausible mechanistic routes were proposed; however, one of the routes was more favourable which involved the formation of a benzoxazine ring first followed by the realization of a triazole ring. Additionally, the more favourable mechanistic route was investigated using DFT studies which suggests that the formations of a Pd(II)-isocyanide complex and α-diazoimino intermediates were key steps in the catalytic cycle.

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

Great progress has been made in the tandem annulation of enynes in the past few years. This review only presents the corresponding reactions of 1,3-enyne structural motifs to provide the functionalized pyridine and pyrrole derivatives. The functionalization reactions cover iodination, bromination, trifluoromethylation, azidation, carbonylation, arylation, alkylation, selenylation, sulfenylation, amidation, esterification, and hydroxylation. We also briefly introduce the applications of the products and the reaction mechanisms for the synthesis of corresponding N-heterocycles.

Synthesis of polysubstituted pyrroles via isocyanide-based multicomponent reactions as an efficient synthesis tool

The present review covers all synthetic methods based on isocyanide-based multicomponent reactions for the preparation of polysubstituted pyrroles as the parent cores of many essential drugs, biologically active compounds, and compounds with wide application in materials science.