Rhodium-Catalyzed Deoxygenation and Borylation of Ketones: A Combined Experimental and Theoretical Investigation

Abstract

The rhodium-catalyzed deoxygenation and borylation of ketones with B 2 pin 2 have been developed, leading to efficient formation of alkenes, vinylboronates, and vinyldiboronates. These reactions feature mild reaction conditions, a broad substrate scope, and excellent functional-group compatibility. Mechanistic studies support that the ketones initially undergo a Rh-catalyzed deoxygenation to give alkenes via boron enolate intermediates, and the subsequent Rh-catalyzed dehydrogenative borylation of alkenes leads to the formation of vinylboronates and diboration products, which is also supported by density functional theory calculations.

The Synthesis of Tetrasubstituted Cycloalkenes Bearing π‐Conjugated Substituents and Their Optical Properties

“…For instance, alkenes bearing four 4,5,9,10-tetrahydropyren-2-yl units can only be synthesized using the McMurry reaction, [20] whereas alkenes bearing two pyrenyl units directly attached to the double bond can be synthesized by means of the McMurry reaction, [21] the Wittig reaction, [22] Horner-Wadsworth-Emmons (HWE) modification, [23] metathesis, [24] carbonyl group condensation, [25] and the rhodium-catalyzed deoxygenation-Suzuki reaction sequence. [26] A similar trend can also be observed in relation to alkenes with two pyrene units that are connected to the double bond via a spacer. Such substances can be efficiently synthesized through the formation of a substituted double-bond moiety via the McMurry reaction [27] or cross-metathesis [28] followed by the Suzuki reaction.…”

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

“…[27][28][29] In 2020, Lisg roup conceived am etal-free version of direct carbonyl deoxyborylation reaction, [30] which was enabled by the unique partnership of the Lewis acidic bis(catecholato)diboron (B 2 cat 2 )a nd the mildly basic N,N-dimethylacetamide (DMA) (Scheme 5E). Amechanism analogous to that in Lius [25][26][27] and Zhaos [28,29] works was proposed, albeit in the absence of the metal catalyst. Of note,t he lability of catecholatoborates in the aqueous environment often induces proto-deboronation.…”

“…Interestingly,t he simple addition of alcohol (e.g., MeOH or EtOH) to the current Cu-catalyzed protocol or using ZhaosR h/PR 3 /B 2 pin 2 /HBpin catalysis completely switched the selectivity to deoxygenative hydroboration. [27][28][29] In 2020, Lisg roup conceived am etal-free version of direct carbonyl deoxyborylation reaction, [30] which was enabled by the unique partnership of the Lewis acidic bis(catecholato)diboron (B 2 cat 2 )a nd the mildly basic N,N-dimethylacetamide (DMA) (Scheme 5E). Amechanism analogous to that in Lius [25][26][27] and Zhaos [28,29] works was proposed, albeit in the absence of the metal catalyst.…”

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

“…A similar scenario could happen with the stepwise addition of pinB‐SiMe 2 Ph as the Nu 2 , achieving a deoxygenative gem ‐silylborylation on the aldehyde/ketone carbonyls ( 5.19 to 5.22 ). Interestingly, the simple addition of alcohol (e.g., MeOH or EtOH) to the current Cu‐catalyzed protocol or using Zhao's Rh/PR 3 /B 2 pin 2 /HBpin catalysis completely switched the selectivity to deoxygenative hydroboration [27–29] …”