Rhodium-catalyzed Borylation of Aryl and Alkenyl Pivalates through the Cleavage of Carbon–Oxygen Bonds

Abstract

Rhodium-catalyzed borylation reactions of aryl and alkenyl pivalates, using a diboron reagent, via the cleavage of carbon–oxygen bonds have been developed. The inert nature of the pivalate moiety enables relatively complex aryl boronates to be synthesized via the tandem cross-coupling of carbon–halogen and carbon–oxygen bonds.

Ni‐Catalyzed Stannylation of Aryl Esters via C−O Bond Cleavage

“…At present, the existing precedents for C−heteroatom bond formation of aryl esters via C−O cleavage remain essentially confined to C−P and C−N bond formations . Aimed at providing better flexibility in synthesis design through further derivatization techniques, aryl esters have recently been converted into aryl trialkylsilanes or aryl boronates via C−O cleavage;, unfortunately, only a limited number of transformations via cleavage of the C−Si bond of aryl trialkylsilanes are within reach, whereas high temperatures and noble catalysts are needed to forge C−B bonds from aryl esters, thus reinforcing a change in strategy. Prompted by our interest in C−O functionalization, we questioned whether an umpolung strategy could be designed to convert electrophilic aryl esters into nucleophilic organotin reagents, superb reaction intermediates for subsequent C−Sn cleavage (Scheme b) .…”

Palladium‐Catalyzed Cross‐Coupling of Alkenyl Carboxylates

“…A major focus of new reaction development is to expand the scope of suitable electrophiles beyond aryl halides . Alkenyl carboxylates, and acetates in particular, are an attractive alternative: they are a convenient source of non‐aromatic functionality, are easily prepared by O‐acylation of ketones, and impart high reaction mass efficiency relative to other leaving groups. Unfortunately, using alkenyl acetates in cross‐coupling remains challenging.…”

C−O Activation by a Rhodium Bis(N‐Heterocyclic Carbene) Catalyst: Aryl Carbamates as Arylating Reagents in Directed C−H Arylation

“…Based on its remarkable activity in C−H activation, we decided to use a rhodium catalyst, even though rhodium complexes are rarely used for C−O bond activation processes . Reported rhodium complexes that can activate the C(aryl)−O bond require the use of a pincer‐type ligand, or boron‐based reagents,– both of which cannot be directly applied to our target C−H/C−O cross‐coupling reactions. We chose ortho arylation of 1 a with aryl carbamate 2 a as our model reaction for catalyst development.…”