From Propargylic Alcohols to Substituted Thiochromenes: gem-Disubstituent Effect in Intramolecular Alkyne Iodo/hydroarylation

One-Pot NIS-Promoted Cyclization/Palladium-Catalyzed Carbonylation for the Selective Synthesis of HFIP Ester-Containing Indenes and Thiochromenes

Practical and atom-economic procedures for the selective synthesis of HFIP ester-containing indenes/thiochromenes from the same propargylic thioethers and HFIP have been developed via one-pot NIS-promoted cyclization/palladium-catalyzed carbonylation. Solvent plays an important role in this transformation, and the reactions proceed selectively and efficiently to afford a variety of HFIP ester-containing indenes and thiochromenes in moderate to excellent yields. In addition, the use of formic acid as the CO source could avoid manipulation of toxic CO gas.

Intramolecular Halogenative-Arylation of Alkynes Using N-halosuccinimide (NXS) Reagents in the CH3CN-H2O System

The cyclizative arylation-halogenation of tethered alkynes has been well explored (particularly for iodo-arylations). It is an important method for the construction of benzo-fused heterocycles as well as carbocycles possessing a halo-olefin. However, to the best of our knowledge, no reaction condition is suitable to promote all three cyclizative halo-arylations, i.e., iodo-arylation, bromo-arylation, and chloro-arylation onto the tethered alkynes is known. Here, we report a set of general reaction conditions for the cyclizative halo-arylation of the tethered alkynes. Our method employs NXS (X = I, Br, Cl) reagents as the source of halonium ion (X+) in the CH3CN and H2O solvent mixture. This process avoids the use of any transition metal catalysts and additives (acids, bases, etc.). It shows broad substrate scope in terms of substitution on both the aryl groups, with yields ranging from 40 to 98%. A large-scale reaction and synthetic modifications of the products were also demonstrated to show the synthetic applicability of the reported procedures.

Development of Glycosylation Protocols Using Glycosyl N-Phenylethynyl Pyrrole-2-carboxylates as Donors

We herein introduce glycosyl N-phenylethynyl pyrrole-2-carboxylates (PEPCs) as novel and highly efficient glycosyl donors. The unique inclusion of the pyrrole group, serving as both an electron-donating group and an ortho-tethering scaffold, imparts exceptional shelf stability while retaining reactivity for glycosylation reactions. PEPC donors exhibit broad utility for both O- and N-glycosylation across a variety of substrates. Additionally, their versatility and efficiency were further demonstrated in a one-pot saccharide synthesis, showcasing their potential for diverse synthetic applications.

Recent developments in thiochromene chemistry

Thiochromenes are versatile sulfur-containing heterocyclic compounds that have received considerable interest in drug discovery because of their ability to act as crucial building blocks for synthesizing bioactive compounds. In particular, these scaffolds have found utility in the design of anticancer, anti-HIV, antioxidant, and antimicrobial agents, among others. Despite their pharmacological potential, the synthesis of these scaffolds is less explored in contrast to their oxygen-containing counterparts. This review classifies the synthetic processes into Michael addition, cycloaddition, ring-opening, coupling, cyclization and Diels-Alder reactions, and others. Reaction mechanisms, circumstances, and important instances are thoroughly discussed in each area. For instance, chiral catalysts and substrates like mercaptobenzaldehyde and cinnamaldehyde are used in Michael addition processes to achieve excellent enantioselectivity. In cycloaddition reactions, readily available substrates such as thioisatins and alkynes achieve regioselectivity and product production. Thiochromenes are also synthesized by ring-opening reactions with epoxides or aziridines. These reactions demonstrate the importance of catalysts and solvents in reaction control, particularly palladium catalysts for aryl halides and thiol coupling processes. Another major class discussed is cyclization reactions with alkynyl thiols and alkynes under regulated temperature and pressure conditions to efficiently synthesize thiochromenes. With the use of chiral substrates and catalysts, Diels-Alder processes increase yields and selectivity and enhance the variety of thiochromene compounds. This review emphasizes the versatility of thiochromenes in drug discovery and consolidates the existing literature on thiochromenes, scrutinizing the gaps and opportunities for synthesizing novel thiochromene-containing lead molecules.

Synthesis of highly substituted 1,3-dienes through halonium promoted 1,2-sulfur migration of propargylic thioethers

Conjugated 1-bromo or 1-iodo-1,3-dienes bearing a sulfide substituent have been synthesized via 1,2-sulfur migration from propargylic thioethers upon activation with NIS or NBS. The reaction generally proceeds with high control over the regio- and diastereoselectivity. Highly substituted thiophenes and selenophenes are easily obtained from the generated dienes.

Ag(I)-Mediated Annulation of 2-(2-Enynyl)pyridines and Propargyl Amines to Access 1-(2H-Pyrrol-3-yl)indolizines

An effective Ag(I)-mediated annulation of 2-(2-enynyl)pyridines and propargyl amines was developed, unexpectedly affording a broad range of functionalized 1-(2H-pyrrol-3-yl)indolizines in moderate to excellent yields. The developed method is characterized by operational simplicity, ready availability of starting materials, high regioselectivity, and broad substrate scope under mild reaction conditions. The Ag(I)-promoted cyclization of 2-(2-enynyl)pyridines and propargyl amines possibly results in the formation of the spiroindolizine, the ring-opening rearrangement of which may give the 1-(2H-pyrrol-3-yl)indolizine. Furthermore, a gram-scale reaction and synthetic transformations are also studied.

Metal-free intramolecular hydroarylation of alkynes

An efficient metal-free intramolecular hydroarylation reaction of alkynes is described here. A series of aryl and N-group attached alkynes generated the intramolecular hydroarylation products in high yields.

Temperature Controlled Di- and Monosulfonylation of Propargyl Alcohols with Sodium Sulfinates: Switchable Access to (E)-Allyl, Vinyldisulfones and Propargyl Sulfones

A switchable di- and monosulfonylation of propargyl alcohols with sodium sulfinates is developed, which successfully affords (E)-allyl, vinyldisulfones and propargyl sulfones in good to excellent yields, respectively. The salient features...

Stereoselective sulfenylation of oxindole-derived propargyl alcohols to access sulfenylated-3-alkenyloxindoles

A Ca-catalyzed, tetrasubstituted alkenyl-sulfenylation was achieved using readily available aryl/alkyl thiols and easily prepared oxindole-derived propargyl alcohols under solvent-free conditions. The reaction proceeded with hydrogen bonding assisted regioselective α-thiolation and subsequent calcium catalyzed stereoselective alkenylation to yield E-alkenyl thioethers with high diastereoselectivity.