Pd-Catalyzed Assembly of Fluoren-9-ones by Merging of C–H Activation and Difluorocarbene Transfer

Abstract

We disclose a novel Pd-catalyzed assembly of fluoren-9-ones by merging of C–H activation and difluorocarbene transfer. ClCF2COONa served as a difluorocarbene precursor to be harnessed as a carbonyl source in this transformation. The current protocol enables us to afford fluoren-9-ones in high yields with excellent functional group compatibility, which also represents the first example of using difluorocarbene as a coupling partner in transition-metal-catalyzed C–H activation.

Multiple-fold C–F bond functionalization for the synthesis of (hetero)cyclic compounds: fluorine as a detachable chemical handle

“…In the search for a viable alternative, Song and co-workers turned to test a combination of readily available ClCF 2 CO 2 Na and K 2 CO 3 as the carbonyl equivalent (Scheme 24). 51 The treatment of ClCF 2 CO 2 Na as a potent coupling partner via difluorocarbene transfer for the palladium-catalyzed C–H carbonylation of 2-iodobiphenyls could synthesize fluoren-9-ones. Of note, this method accommodated a diverse set of 2-iodinebiphenyls substrates regardless of the varied nature of substituents, simultaneously obviating the straight utility of highly pressurized CO.…”

Palladium-Catalyzed Sequential Vinyl C–H Activation/Dual Decarboxylation: Regioselective Synthesis of Phenanthrenes and Cyclohepta[1,2,3-de]naphthalenes

“…For instance, a convenient and general palladium-catalyzed aryne annulation to synthesize phenanthrenes via arylpalladium­(II) aryne insertion and an intramolecular exo/endo-Heck reaction was reported by the groups of Larock and Yao, respectively . Very recently, a C­(aryl), C­(aryl)-palladacycle generated from 2-iodobiphenyls underwent two cross-coupling steps to attain the functionalization of both carbon atoms, as discovered and developed by the Zhang, Wang, Song, Liu, Xiang, Yang and Liang, and Luan groups, providing a feasible and reliable sequential synthetic strategy for the construction of PAHs. Despite significant advancements, there are still some limitations: (1) Electron-withdrawing groups are required, and the regioselective carbopalladation of asymmetric arynes is totally uncontrollable.…”

Rhodium-Catalyzed Reductive trans-Alkylacylation of Internal Alkynes via a Formal Carborhodation/C–H Carbonylation Cascade

“…Transition-metal-catalyzed carbonylation of C–H bonds has become a fundamental and powerful methodology in synthesis and has been extensively applied to build versatile carbonyl-based compound frameworks that are present in nature products, pharmaceuticals, agrochemicals, fragrance chemistry, and functional materials . Typical approaches for the assembly of a wide variety of ketones, including diaryl ketones, aryl alkyl ketones, and dialkyl ketones, have been significantly developed in recent decades and are very attractive due to their high atom-/step-economy and avoidance of the requirement of prefunctionalized reaction partners. − In contrast to the impressive progress made in the carbonylation of various aromatic C­(sp 2 )–H bonds in precursors, such as directing-group-based arenes and heteroarenes, with aryl halides, aromatic organometallics, or inherent arenes/nucleophilic arenes to assemble diaryl ketones, similar versions of carbonylation of aromatic C­(sp 2 )–H bonds with unsaturated hydrocarbons such as alkenes , or alkynes have been much less reported (Scheme A), which has been pioneered by the group of Moore through a Ru 3 (CO) 12 -catalyzed carbonylation of pyridine C­(sp 2 )–H bonds with carbon monoxide (CO) (150 psi; 10.56 atm) and terminal alkenes at 180 °C for the synthesis of pyridyl alkyl ketones (Scheme A-a). From a formal point of view, these methods all rely on transition-metal-catalyzed transfer hydrogenation via the chelation-assisted insertion of Ru 3 (CO) 12 into the C­(sp 2 )–H bonds to generate the ruthenium hydride complex, followed by addition across a π-system (often alkenes) and transfer hydrogenation reductive carbonylation of the alkene with a CO cascade to access aryl alkyl ketones.…”