Jie Wu

As valuable C1 building blocks, isocyanides represent an important class of reactive species and synthons. During the past decades, exhaustive efforts have been devoted to the discovery of highly efficient reactions involving isocyanide on the basis of the development of the Passerini and Ugi reactions. Several types of reactions involving isocyanides have been reported, such as nucleophilic attack, electrophilic addition, imidoylation reactions, and oxidation etc. In this review, recent progress in isocyanide insertion chemistry is presented. Among all isocyanide insertions, two catalytic systems have been developed, that is, Lewis (Brønsted) acid-catalyzed isocyanide insertions and transition-metal-enabled isocyanide insertions, respectively. This review is hence written in the sequence of Lewis (Brønsted) acid-catalyzed isocyanide insertion and transitional metal-enabled isocyanide insertion, where isocyanide insertion into heteroatom-hydrogen bonds, carbon-halogen bonds, carbon-hydrogen bonds, and metal carbenes are summarized.

Pyridinium salts are valuable building blocks, which have been widely applied in various organic transformations during the past few decades. In particular, N-functionalized pyridinium salts have been explored as convenient radical precursors, which would go through reductive single-electron transfer. As a result, the chemistry of such pyridinium compounds for generating carbon-, nitrogen-, and oxygen-centered radicals has been witnessed, and a remarkable progress has been achieved, making it a hot topic over the last five years. This Review describes recent advances in the area of pyridinium salts as radical precursors, concerning the development of radical reactions involving pyridinium salts in organic synthesis.

This review is focused on the recent advances in the chemistry of sulfur dioxide fixation through a radical process. Diverse sulfonyl compounds can be obtained efficiently under mild conditions.

A catalyst-free approach for the generation of sulfonyl radicals from aryldiazonium tetrafluoroborates in the presence of DABCO⋅(SO2 )2 is realized. The combination of aryldiazonium tetrafluoroborates, DABCO⋅(SO2 )2 , and aryl propiolates affords 3-sulfonated coumarins in good to excellent yields. This tandem reaction process involves radical addition, spirocyclization, and 1,2-migration of esters. Additionally, the in situ diazotization of a number of anilines allows the directional synthesis of desired 3-sulfonated coumarins in a one-pot, two-step process.

The coupling of aryldiazonium tetrafluoroborates, DABCO⋅(SO2)2, and hydrazines under metal-free conditions leads to the formation of aryl N-aminosulfonamides. The reaction proceeds smoothly at room temperature and shows broad functional-group tolerance. A radical process is proposed for this transformation.