Decarboxylative Conjunctive Cross‐coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

Abstract

The synthesis of complex alkyl boronic esters through conjunctive cross‐coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross‐coupling cascade of vinyl boronic esters. Excellent functional‐group tolerance is displayed, and application of a range of carboxylic acids, including secondary α‐amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross‐coupling was also applied to the synthesis of sedum alkaloids.

Iron-Catalyzed Enantioselective Multicomponent Cross-Couplings of alpha-Boryl Radicals

“…In addition, this method tolerates a range of electronrich and -poor meta-and para-substituents including C-Cl bonds that can be further handles in cross-coupling reactions (10)(11). [19][20] Finally, extended π-systems work well in this transformation albeit modest enantiomeric ratios were observed for some systems (15)(16)(17)(18). Notably, x-ray analysis of 18 unambiguously determined the absolute stereochemistry of the major enantiomer as (S).…”

“…Herein we report the first general and broadly applicable use of commercially available iron salts and chiral bisphosphine ligands to promote asymmetric multicomponent radical cross-coupling between a range of (difluoro)alkyl halides, Grignard reagents, and vinyl boronates. Based on prior work by us 11f and others, [14][15][16][17] we initiated our studies using tert-butyl bromide, vinylB(pin), and 4fluorophenylmagnesium bromide as model substrates to investigate the asymmetric three-component iron-catalyzed CCR. We hypothesized that under slow addition of Grignard reagent, we could generate the active chiral monoaryl-and Table 1.…”