Synthesis of different types of valerolactams starting from 2,5-dihydrooxazoles

Still Relevant Today: The Asinger Multicomponent Reaction

The Asinger multicomponent reaction is a versatile synthetic tool which gives access to multiple drug-like scaffolds such as 3-thiazolines. The diversity and easy access of its starting materials, its operational simplicity combined with mild conditions and relatively good yields, renders the Asinger reaction, today more than ever, a cornerstone not only in heterocyclic chemistry and modern synthesis but also in medicinal chemistry. In this review, we perform a thorough analysis of the scope and limitations on the different reaction variants with their starting materials, the three-dimensional solid-state conformations of the Asinger derivatives, and we underline and classify all the major post-modifications that have been described. In addition, we report all the major applications in drug discovery projects.

Silver-Promoted Site-Selective Intramolecular Cyclization of 2-Methylthiobenzamide Through α-C(sp3)-H Functionalization

Silver-mediated intramolecular α-C(sp³)-H bond functionalization of the methylthio group has been established in the presence of Selectfluor as an additive. This novel strategy provides efficient access to various diverse sulfur-based heterocycles with good yields and functional group compatibility. It is noteworthy that the completely novel benzooxathiin-4-imine skeletons were reported for the first time in this study.

Double 1,4-addition of (thio)salicylamides/thiosalicylic acids with propiolate derivatives: a direct, general synthesis of diverse heterocyclic scaffolds

A simple and practical ring-closure procedure to prepare a range of diverse heterocycles has been developed.

Three-component reaction toward polyannulated quinazolinones, benzoxazinones, and benzothiazinones

An efficient conversion of readily accessible cyclic imines with acid chlorides, that are able to take part in nucleophilic aromatic substitution (SNAr) reactions is realized in a new three-component, one-pot reaction, giving at least tricyclic annulated quinazolinones, benzoxazinones, and benzothiazinones as a result of the employed nitrogen, oxygen, or sulfur nucleophiles, respectively. Especially in the case of quinazolinones, this convenient strategy enables the access to heterocycles of heightened diversity, which offer the development of efficient derivatizations of the elaborated heterocyclic scaffolds. In a subsequent Heck or Ullmann cyclization, further annulations to the mentioned quinazolinones can be carried out.

Direct imine acylation for molecular diversity in heterocyclic synthesis

Imines and carboxylic acids have been directly coupled using propylphosphonic acid anhydride and NEt(i-Pr)2 to give N-acyliminium ions, which were intramolecularly trapped with oxygen, nitrogen, sulfur, and carbon nucleophiles to provide a wide range of structurally diverse heterocycles.