Current Organic Chemistry - Volume 23, Issue 22, 2019

Thio-, seleno-substituted triazoles are useful scaffolds employed in the fields of organic synthesis, medicinal chemistry, and material science. A number of synthetic approaches to efficient formation of thio- and seleno-triazoles have been disclosed, including the interception of copper(I) triazolides generated in-situ, cycloaddition of internal alkynes (thio-, halo-, and metalated alkynes) to azides, and the coupling of azides and nonalkyne substrates. This mini-review intends to summarize the synthetic methods toward thio-, seleno-1,2,3-triazoles and the relative reaction mechanisms.

C-N bond formation reactions are the most important transformations in (bio)organic chemistry because of the widespread occurrence of amines in pharmaceuticals, natural products, and biologically active compounds. The Hofmann rearrangement is a well-known method used for the preparation of primary amines from amides. But, the traditional version of the Hofmann rearrangement often gave relatively poor yields due to over-oxidation or due to the poor solubility of some amides in aqueous base, and created an enormous amount of waste products. Developments over the last two decades, in particular, have focused on refining both of these factors affecting the reaction. This review covers both the description of recent advances (2000-2019) in the Hofmann rearrangements and its applications in the synthesis of heterocycles, natural products and complex molecules of biological interest. It is revealed that organo-catalytic systems especially hypervalent iodine-based catalysts have been developed for the green and environmentally friendly conversion of carboxamides to primary amines and carbamates.

γ-Hydroxybutenolides (γ-HB) is an important structural core found in many bioactive marine natural products (MNPS). The γ-HB core containing NPS served as an inspiration to medicinal chemists to undertake designing of the new synthetic strategies to construct γ-HB core. Subsequently, it further results in the development of novel physiological and therapeutic agents. The most notable example includes manoalides, cacospongionolides, petrosaspongioide M and dysidiolide from marine sponges possessing anti-inflammatory properties. γ-HB containing MNPS were known to possess various pharmacological properties such as antimicrobial (acantholide B), cytotoxic (acantholide A-E, spongianolide A), inhibitors of secretory phospholipase A2 (cladocorans A and B), BACE inhibitors (ianthellidone G), etc. Moreover, the γ-HB moiety was explored as antifouling agents as well. Owing to their numerous biological activities and attractive molecular structures, there are lots of advances in the synthetic methodology of these compounds. This review gives the account on isolation and biological studies of MNPS with γ-HB skeleton as a core unit. Furthermore, the synthesis of selective γ-HB containing bioactive MNPS like manoalide, secomanoalide, cacospongionolides, luffarielloide and dysidiolide were highlighted in the article.

The palladium-catalyzed reaction of aryl halide and boronic acid for the formation of C–C bonds so-called Suzuki–Miyaura cross-coupling reaction has many applications in Modern Synthetic Organic Chemistry. In 2013, we emphasized the applications of the intramolecular Suzuki cross-coupling reaction in cyclization and heterocyclization. Due to a plethora relevant papers appeared in the chemical literature, herein, we wish to cover by updating our previous review, the applications of the intramolecular Suzuki cross-coupling reaction in cyclization and heterocyclization leading to various homocyclic and heterocyclic compounds reported during a period of 2013 to 2018.

Synthesis of symmetrical 1,3-diynes from terminal alkynes through an oxidative process is generally called Glaser coupling. The classic Glaser coupling is catalyzed by copper salts under an atmosphere of molecular oxygen as an oxidant. Over the past years, different metal catalysts and oxidants were successfully used in this atom economical C-C coupling reaction. Moreover, several procedures for the preparation of unsymmetrical 1,3-diynes by coupling two different alkyne substrates have been developed. In this review, we will highlight the usefulness of transition metal nanoparticles as efficient catalysts in homo- and hetero-coupling of alkynes by hoping that it will be beneficial to the development of novel and extremely efficient catalytic systems for this fast-growing and important reaction.