Decarbonylation of benzaldehydes by dual photoorgano-cobalt catalysis

Abstract

We report a mild alternative to thermally-driven noble-metal catalyzed decarbonylation protocols for the defunctionalization of benzaldehydes in short reaction times. Our cooperative photocatalytic system involves thioxanthone as an inexpensive HAT-agent...

Photocatalytic Dehydroformylation of Benzyl Alcohols to Arenes

“…Based on the above observations and according to previous studies, [9,11,14] we proposed a plausible mechanism for the dehydroformylation of benzyl alcohols (Scheme 4). In the transformation, a stepwise radical mechanism could be involved, proceeding via photoinduced CÀ H activation.…”

“…To further test this hypothesis, we subjected the proposed aldehyde intermediate (1-ald) to our reaction conditions (Scheme 3c), which underwent decarbonylation to give 1 b in excellent yield (93 %). According to our previous work on the photocatalytic decarbonylation of benzaldehydes, [11] such a dual HAT-cobalt system performs well in the defunctionalization of aromatic aldehydes. In contrast, subjecting substrate 31 a to our conditions led to no arene formation (Scheme 3d), as the protection of the alcohol group prevents the initial dehydrogenation event.…”

“…Alternatively, the Zuo group successfully employed cerium complexes for the photocatalytic transformation of alcohols by formaldehyde extrusion. [10] Inspired by these methodologies and by our previous work on the photocatalytic decarbonylation of benzaldehydes (Scheme 1b), [11] we hypothesized that a two-step dehydroformylation sequence might unlock benzyl alcohols as substrates for their defunctionalization to arenes (Scheme 1c). For this purpose, an acceptorless light-driven HAT-cobalt system held positive prospects.…”

Direct Observation of Triplet States in the Isomerization of Alkenylboronates by Energy Transfer Catalysis

“…Thioxanthone (TX) has a venerable history in the vibrant arena of energy transfer catalysis − but despite its popularity, delineating the mechanistic nuances of reactions mediated by this popular organocatalyst is complicated by its nonemissive triplet state. − In contrast to many photoactive metal complexes, − invoking TX room-temperature emission quenching in support of triplet energy transfer is inappropriate, and thus, unifying catalysis data with detailed photophysical investigations would be highly enabling for future reaction design. Of the multitude of photochemical processes mediated by thioxanthone with hydrogen abstraction, electron transfer or energy transfer events being mechanistic key steps, ,− this low molecular weight catalyst has proven to be highly adept in facilitating the geometric E → Z isomerization of a plenum of activated alkenes. − Furthermore, the deracemization of chiral alkenes catalyzed by chiral TX derivatives has also recently been reported . Representative deployments include the isomerization of β-boryl acrylates, − elaborately substituted fumarates, , and photocatalytic cascade reactions to generate well-defined drug discovery vectors. , These transformations are assumed to occur by selective energy transfer from excited state thioxanthone (TX*) to the starting E -isomer: upon excitation, a transient triplet state intermediate is generated that can be processed to either the substrate or product isomers, thereby accumulating the Z -isomer in the reaction mixture (an energy diagram explaining this mechanism for our specific substrate is presented in the Results and Discussion section).…”

Regioselective Aldehyde Decarbonylation through Palladium-Catalyzed Nitrile Boronic Acid Cross-Coupling

“…5 However, the removal of aldehydes is challenging and often requires harsh conditions and metals including Rh, 6 Ni, 7 Ru, 8 Ir, 9 and Pd. 10 More recently, nanoparticles, 11 photocatalysts, 12 and microwave conditions 13 have been employed to overcome the high cost and harsh conditions associated with these catalysts. Additionally, many reports utilize an aldehyde scavenger to minimize catalyst poisoning.…”