Enantioselective Construction of Carbocyclic and Heterocyclic Tertiary Boronic Esters by Conjunctive Cross-Coupling Reaction

Asymmetric synthesis of atropisomers featuring cyclobutane boronic esters facilitated by ring-strained B-ate complexes

The strain-release-driven reactions of bicyclo[1.1.0]butanes (BCBs) have received significant attention from chemists. Notably, 1,2-migratory reactions enabled by BCB-derived B-ate complexes effectively complement the reactions initiated by common BCBs. The desired products are particularly valuable for late-stage transformations due to the presence of the C-B bond. However, asymmetric reactions mediated by BCB-derived boronate complexes have progressed slowly. In this study, we develop an asymmetric synthesis of atropisomers featuring cis-cyclobutane boronic esters facilitated by 1,2-carbon or boron migration of ring-strained B-ate complexes, achieving high enantioselectivity. The reaction is compatible with various aryl, alkenyl, alkyl boronic esters and B2pin2, and shows good compatibility with natural product derivatives. Mechanistic studies are conducted to understand stereoselective control in the dynamic kinetic asymmetric transformations (DYKATs). The target products can undergo a series of transformations, further demonstrating the practicality of this methodology.

The reactivity of alkenyl boron reagents in catalytic reactions: recent advances and perspectives

Recent advances focusing on novel reactivity of alkenyl boron reagents in polar or radical pathways within catalytic reactions by employing transition metal catalysis, organocatalysis have been summarized and discussed.

Asymmetric Synthesis of Chiral 1,2-Bis(Boronic) Esters Featuring Acyclic, Non-Adjacent 1,3-Stereocenters

The construction of acyclic, non-adjacent 1,3-stereogenic centers, prevalent motifs in drugs and bioactive molecules, has been a long-standing synthetic challenge due to acyclic nucleophiles being distant from the chiral environment. In this study, we successfully synthesized highly valuable 1,2-bis(boronic) esters featuring acyclic and nonadjacent 1,3-stereocenters. Notably, this reaction selectively produces migratory coupling products rather than alternative deborylative allylation or direct allylation byproducts. This approach introduces a new activation mode for selective transformations of gem-diborylmethane in asymmetric catalysis. Additionally, we found that other gem-diborylalkanes, previously challenging due to steric hindrance, also successfully participated in this reaction. The incorporation of 1,2-bis(boryl)alkenes facilitated the diversification of the alkenyl and two boron moieties in our target compounds, thereby enabling access to a broad array of versatile molecules. DFT calculations were performed to elucidate the reaction mechanism and shed light on the factors responsible for the observed excellent enantioselectivity and diastereoselectivity. These were determined to arise from ligand-substrate steric repulsions in the syn-addition transition state.

Synthesis of substituted benzylboronates by light promoted homologation of boronic acids with N-sulfonylhydrazones

The synthesis of benzylboronates by photochemical homologation of boronic acids with N-tosylhydrazones under basic conditions is described. The reaction involves the photolysis of the N-tosylhydrazone salt to give a diazoalkane followed by the geminal carboborylation of the diazoalkane. Under the mild reaction conditions, the protodeboronation of the unstable benzylboronic acid is circumvented and the pinacolboronates can be isolated after reaction of the benzylboronic acid with pinacol. The metholodogy has been applied to the reactions of alkylboronic acids with N-tosylhydrazones of aromatic aldehydes and ketones, and to the reactions of arylboronic acids with N-tosylhydrazones of aliphatic ketones. Moreover, the employment of the DBU/DIPEA bases combination allows for homogeneous reactions which have been adapted to photochemical continuous flow conditions. Additionally, the synthetic versatility of boronates enables their further transformation via Csp3-C or Csp3-X bond forming reactions converting this methodology into a novel method for the geminal difunctionalization of carbonyls via N-tosylhydrazones.