Azides are important intermediates in organic synthesis. They can function as precursors to form amines, amides, quinolones, pyridines, triazoles, amidines, indoles, and so on. Although there are some reviews about the applications of azides, few are concerned about their fundamental mechanisms. This review will focus on recent advances of azides based on three reactivity patterns, which may enlighten the further research.
Abstract2‐Propargyl alcohols are widely used in organic reactions. Their great success is rooted in the presence of multiple functional groups. This review will focus on six types of mechanisms: (i) 2‐propargyl alcohols as carbocation precursors, (ii) alkynes as electrophiles, (iii) alcohols as nucleophiles, (iv) fracture via ketones or elimination into alkene intermediates, (v) oxidation into alkynyl‐ortho‐quinone methides or carbonyl intermediates, and (vi) ring expansions. Reactions involving alkanes, alkenes, alkynes, arenes, alcohols, amines, amides, ketones, CO2, hydrazine, iodobenzene, azides, carbenes, arylboronic acids, etc. will be discussed. We hope that this review will help to promote future research in this area.magnified image
Sulfonyl hydrazides are widely used as organic reagents. Advances in the past decade are summarized in the following categories by key intermediates: (1) [RO2S.]; (2) RO2SSR; (3) [ArS.]; (4) [RO2S−]; (5) RSO2‐[Metal] species; (6) Ar‐[Metal] species; (7) RSX; (8) RS‐DBU; (9) nucleophilic amino group; (10) sulfonyl hydrazides as diazene or sulfinic acid surrogate. Reactions with alkenes, alkynes, aldehydes, alcohols, thiophenol, Grignard reagents, among others, are discussed. We hope this review will promote future research in this area.
The development of a methodology for the preparation of arylboronic acids or arylboronates is of significant interest to organic chemists. Classical synthetic methods to prepare these organoboron compounds are based on the reaction of Grignard or lithium reagents with trialkyl borates. In the past few decades, the transition‐ metal‐catalyzed borylation of aryl halides, or pseudohalides, and C–H bonds of hydrocarbons has been a powerful tool for the synthesis of arylboronates in modern organic synthesis. These transformations are generally considered to proceed via organometallic intermediates generated by oxidative addition or transmetalation processes from the boron reagent. Several reviews on this type of borylation catalyzed by transition metals have been published in the literature. Interestingly, there has been a novel recognition that the boron reagent can participate in free‐radical coupling via the homolytic cleavage of the boron‐boron bond in recent years. In this review, recent advances in this new area of boron chemistry are summarized and the reaction mechanisms are also discussed.
An efficient metal-free sulfenylation of indoles with disulfides has been developed, leading to 3-arylthioindoles in moderate to excellent yields. Furthermore, bromosulfenylation of indoles with disulfides has been realized for the first time providing a new family of 2-bromo-3-arylthioindole derivatives in good yield by the one-pot construction of C À S and C À Br bonds. It is noteworthy that the system enables the use of both the RS moieties in RSSR and shows a broad functional group tolerance.
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