Recently, gem-diborylalkanes have attracted much attention as versatile building blocks and fundamental intermediates in organic synthesis, because they enable multiple C-C bond construction and further transformation at C-B bonds. Importantly, gem-diborylalkanes can be utilised as bisnucleophilic partners in a variety of chemo-selective C-C bond-forming reactions. This review describes recent developments in synthesising gem-diborylalkanes in complex molecules along with their chemical transformation. In the first part of the review the different synthetic approaches used to synthesise gem-diborylalkanes are described. In the second part, an overview of the chemoselective transformation of gem-diborylalkanes into various functionalized materials is discussed along with one-carbon homologation of diborylmethane via a selective uni- and bidirectional method.

Herein we describe a cobalt-catalyzed C-H activation of aryl and heteroaryl sulfonamides and their intermolecular heteroannulation reaction with allenes, providing a convergent strategy for the synthesis of biologically interesting heterocyclic scaffolds. Carbometallation of allenes proceeds selectively through a Co-alkenyl pathway for a wide range of electron-poor and electron-rich allenes.

The first example of simple Re(2)O(7)-catalyzed direct dehydrative coupling between allylic alcohols with electron-deficient amines has been achieved under mild and open flask conditions. The protocol has also been successfully applied to benzylic and propargylic alcohols. The mechanistic proof for the S(N)1-type process has also been provided.

Cobalt‐catalyzed sp2 C−H bond functionalization of diarylphosphinamides with heterobicyclic alkenes was demonstrated at room temperature employing commercially available cobalt(II)‐salts. The effectiveness of this strategy was illustrated with the reaction of various 8‐aminoquinoline derived phosphinic amides and 7‐oxa/azabenzonorbornadienes. The reaction conditions exhibited excellent functional group tolerance and high diastereoselectivities. Furthermore, extension of this approach to the preparation of polyaryl cyclic phosphinamides was achieved through the dehydrative ring opening/aromatization sequence.magnified image

A new palladium-catalyzed intramolecular oxidative cycloisomerization of readily available starting materials, 2-cinnamyl-1,3-dicarbonyls, has been demonstrated for the creation of structurally diverse 2-benzyl furans. The cycloisomerization occurs by a regioselective 5-exo-trig pathway. The reaction shows a broad substrate scope with good to excellent yields. Furthermore, a one-pot procedure has been executed by using readily available cinnamyl alcohols and 1,3-diketones.

An unprecedented dehydrative C-C bond formation between unprotected anilines with benzyl alcohols is disclosed. Re2O7 catalyst (5 mol %) at elevated reaction temperature (80 °C) provided C-benzylanilines with high to excellent yields and with good chemoselectivities (over N-alkylation). A probable mechanism has been proposed based on mechanistic studies.

Air-/moisture-stable, crystalline, and storable chiral salicyloxazoline based oxorhenium(V) complexes have been synthesized and their catalytic application for the asymmetric reduction of ketimines using hydrosilane as hydride source is disclosed. A broad substrate scope, high yields, and excellent enantioselectivities (up to 99 %) are attained. Furthermore, the syntheses of enantiopure α-amino esters, γ- and δ-lactams, and isoindolinones have also been carried out using this methodology. Finally, the method has been applied to synthetic targets of pharmaceutical relevance, such as R-(+)-salsolidine and R-(+)-crispine A.

Partially saturated nitrogen heterocycles are versatile building blocks for the preparation of other nitrogen heterocycles. For example, dihydropyridines can be converted to pyridines, tetrahydropyridines, and piperidines through oxidation, reduction, and functionalization reactions, respectively. Dearomatization of heteroarenes is an attractive approach for the synthesis of partially saturated heterocycles such as dihydropyridines due to the wide availability of heteroarenes. Significant research efforts have been dedicated to the addition of nucleophiles to various heteroarenium salts in this direction using organoboron or organometallic reagents. The availability of organoboron and organometallic coupling partners has been an important limitation to this chemistry. Direct coupling of electrophiles with heteroareniums could significantly improve the scope of these dearomatization reactions due to the wider availability of electrophiles compared to nucleophiles such as organoboron and organometallic reagents. Herein, we report the coupling of aryl iodides with pyridinium and related heteroarenium salts catalyzed by Ni/bpp and an Ir photocatalyst using Zn as a terminal reductant. This methodology tolerates a wide range of functional groups and allows the coupling of aryl and heteroaryl iodides, thus significantly expanding the scope of nitrogen heterocycle scaffolds that could be prepared through dearomatization of heteroarenes. The reaction products have been further functionalized to prepare various nitrogen heterocycles. Initial mechanistic studies indicate that the reaction described herein goes through a unique mechanism involving dimers of dihydroheteroarenes.