10.1002/anie.201700195
The study reports a Pd-catalyzed asymmetric reductive Heck reaction using diboron–water as a hydride source. The researchers used N-aryl acrylamides as substrates and Pd(OAc)2 as the catalyst, along with tBuPhOX as the ligand and tetrahydroxydiboron as the diboron reagent. The reaction proceeds via intramolecular asymmetric carbopalladation of the substrates, followed by reduction of the C(sp3)-Pd intermediate using water as the hydride source, yielding enantioenriched 3,3-disubstituted oxindoles with high yields and enantioselectivities. The ligand plays a crucial role in determining both the enantioselectivity and the reaction pathways, allowing for either hydroarylation (reductive Heck) or carboborylation products. The study also demonstrates the synthesis of deuterated compounds by using heavy water (D2O) as a deuterium donor in combination with bis(catecholato)diboron.
10.1021/acs.orglett.0c02367
This research presents a novel synthetic strategy for the radical difluoroalkylation of internal alkynes to produce fluoroalkyl-substituted alkenes with a pendant aldehyde or ketone moiety. The study investigates the use of tetrahydroxydiboron [B2(OH)4] as a promoter for this radical addition reaction, which is initiated through N,N-dimethylformamide-assisted homolytic cleavage of the B-B bond. The authors optimized the reaction conditions, finding that the presence of B2(OH)4, a base (K2CO3), and a nickel complex (NiCl2·DME) with 1,10-phenanthroline as a ligand in DMF solvent at room temperature yielded the best results. The scope of the reaction was explored with various alkynol substrates and fluoroalkyl halides, demonstrating compatibility with a range of functional groups and achieving moderate to good yields. Control experiments and mechanistic studies suggest that B2(OH)4 plays a crucial role in initiating the radical process, potentially serving as a mild, low-toxicity radical initiator. This work highlights a convenient and versatile method for synthesizing fluoroalkylated alkenes, which are valuable building blocks in organic synthesis, and opens new avenues for the application of tetrahydroxydiboron in organic transformations.
