Tetrahydroxydiboron has previously been used as a borylation or reducing reagent in organic synthesis. Herein, we present a novel tetrahydroxydiboron-promoted radical addition of internal alkynes followed by intramolecular oxidation of alcohol through 1,5-hydrogen atom transfer. Preliminary mechanistic studies showed that the process might be initiated through N,N-dimethylformamide-assisted homolytic cleavage of tetrahydroxydiboron. This process provides a convenient synthesis of fluoroalkyl-substituted alkenes with a pendant aldehyde or ketone moiety.

Herein we report a hydrogen-bonding controlled nickel-catalyzed regioselective cyclotrimerization of terminal alkynes in moderate to excellent yields with high regioselectivities toward 1,3,5-trisubstituted benzenes. This method features a cheap catalyst, mild reaction conditions, and excellent functional group compatibility. The Ni–B­(OH)2 complex in situ generated from NiCl2·DME and tetrahydroxydiboron might act as an active catalyst. After three consecutive cis-additions of terminal alkynes, internal migratory insertion cyclization, and β-boron elimination induced aromatization, 1,3,5-trisubstituted benzenes were selectively established.

The reactivity of N-difluoromethylpyridinium salts is seldom explored because of their instability and low availability. Here we present a novel nucleophilic addition of N-difluoromethylpyridinium salts with nitroalkanes to synthesize N-CF2H-dihydropyridines and N-CHO-dihydropyridines in a highly efficient and regioselective pathway. This protocol exhibits good functional group tolerance and good to excellent yields.

Phenothiazine derivatives have attracted tremendous research attention due to their rich redox-active properties. In this work, a phenothiazine-based, highly crystalline, and two-dimensional covalent organic framework (PTz-An-COF) was developed. PTz-An-COF exhibited a low bandgap of 1.92 eV with a broad visible-light absorption. Interestingly, PTz-An-COF can serve as an efficient photoinitiator for visible-light-induced radical polymerization of methyl acrylate. Remarkably, PTz-An-COF as a photoinitiator can be easily recycled and maintains the same catalytic activity as that of pristine PTz-An-COF. This work provides new insights into the development of high-performance heterogeneous photocatalysts for radical polymerization.

No abstract