I2-Catalyzed sulfenylation of indoles and pyrroles using triethylammonium thiolates as sulfenylating agents

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Among the known aromatic nitrogen heterocycles, pyrrole represents a privileged aromatic heterocycle ranging its occurrence in the key component of "pigments of life" to biologically active natural products to active pharmaceuticals. Pyrrole being an electron-rich heteroaromatic compound, its predominant functionalization is legendary to aromatic electrophilic substitution reactions. Although a few excellent reviews on the functionalization of pyrroles including the reports by Baltazzi in 1963, Casiraghi and Rassu in 1995, and Banwell in 2006 are available, they are fragmentary and over fifteen years old, and do not cover the modern aspects of catalysis. A review covering a comprehensive package of direct functionalization on pyrroles via catalytic and non-catalytic methods including their translational potential is described. Subsequent to statutory yet concise introduction, the classical functionalization on pyrroles using Lewis acids largely following an ionic mechanism is discussed. The subsequent discussion follows the various metal-catalyzed C-H functionalization on pyrroles, which are otherwise difficult to implement by Lewis acids. A major emphasize is given on the radical based pyrrole functionalization under metal-free oxidative conditions, which is otherwise poorly highlighted in the literature. Towards the end, the current development of pyrrole functionalization under photocatalyzed and electrochemical conditions is appended. Only a selected examples of substrates and important mechanisms are discussed for different methods highlighting their scopes and limitations. The aromatic nucleophillic substitution on pyrroles (being an electron-rich heterocycle) happened to be the subject of recent investigations, which has also been covered accentuating their underlying conceptual development. Despite great achievements over the past several years in these areas, many challenges and problems are yet to be solved, which are all discussed in summary and outlook.

Recent Advances in Iodine-Promoted C-S/N-S Bonds Formation

Sulfur-containing scaffold, as a ubiquitous structural motif, has been frequently used in natural products, bioactive chemicals and pharmaceuticals, particularly C-S/N-S bonds are indispensable in many biological important compounds and pharmaceuticals. Development of mild and general methods for C-S/N-S bonds formation has great significance in modern research. Iodine and its derivatives have been recognized as inexpensive, environmentally benign and easy-handled catalysts or reagents to promote the construction of C-S/N-S bonds under mild reaction conditions, with good regioselectivities and broad substrate scope. Especially based on this, several new strategies, such as oxidation relay strategy, have been greatly developed and accelerated the advancement of this field. This review focuses on recent advances in iodine and its derivatives promoted hybridized C-S/N-S bonds formation. The features and mechanisms of corresponding reactions are summarized and the results of some cases are compared with those of previous reports. In addition, the future of this domain is discussed.

T3P® mediated domino C(sp2)–H sulfenylation/annulation of enaminones and methylsulfinyls for the synthesis of chromone thioether derivatives

Regio-selective preparation of 3-sulfenylated chromone using T3P® has been described for the first time.

Metal-Free Synthesis of 2-Aminobenzothiazoles via Iodine-Catalyzed and Oxygen-Promoted Cascade Reactions of Isothiocyanatobenzenes with Amines

In this paper, a highly efficient and sustainable synthesis of 2-aminobenzothiazoles through the cascade reactions of isothiocyanatobenzenes with primary or secondary amines by using iodine as a catalyst and oxygen as an oxidant is presented. Mechanistically, the formation of the title compounds involves the in situ formation of the required benzothiourea intermediate followed by its intramolecular cross dehydrogenative coupling of a C(sp²)-H bond and a S-H bond. To our knowledge, this should be the first example in which 2-aminobenzothiazoles are efficiently prepared from simple and cheap isothiocyanates and amines under metal-free conditions by using iodine as a catalyst and molecular oxygen as an oxidant with water as the byproduct. Compared with literature protocols, this method eliminates the use of ortho-halo-substituted precursors, expensive transition-metal catalysts, and hazardous oxidants.

I2-Catalyzed cross dehydrogenative coupling: rapid access to benzoxazinones and quinazolinones

An efficient and applicable I₂-catalyzed intramolecular dehydrogenative C–O/C–N coupling reaction has been developed for the first time to provide both benzoxazinones and quinazolinones.

Facile synthesis of benzo[b]thiophenes via metal-free radical-triggered intramolecular C–S bond formation

A facile method for the synthesis of benzo[b]thiophenes with good to excellent yields via metal-free intramolecular C–S bond formation has been developed by utilizing I₂ as a catalyst and O₂ from air as an oxidant (20 examples).