Process Development for a 1H-Indazole Synthesis Using an Intramolecular Ullmann-Type Reaction.

Within the scope of developing a new route to an active pharmaceutical ingredient intermediate, we had need of a fluorinated indazole. Although an established route was in place, it was undesirable due to safety and selectivity concerns. A concise and improved route was developed to form the desired indazole, which takes advantage of an electronically directed metalation/formylation sequence followed by condensation with methyl hydrazine to form a hydrazone and culminates in a copper-catalyzed intramolecular Ullmann cyclization. The Ullmann reaction was plagued with difficulties ranging from poor reactivity to thermal hazard concerns, but use of high-throughput screening, statistical modeling, and an unusual isolation method for fine chemicals, safe and optimal conditions were found that produce high-purity isolated material in excellent yields at a laboratory scale.

Defluorodearomatization: A Photocatalytic Birch-Like Reduction That Enables C-C Bond Formation and Provides Access to Unnatural Cannabinoids.

Within the framework of discovery chemistry, polyfluorination remains a synthetic challenge despite its ability to provide useful characteristics, such as a reduction in the number of hydrogen bond donors and metabolic stability. Coupling a reversal of this methodology with photocatalysis has been demonstrated to allow the rapid synthesis of previously difficult or impossible targets by starting with fluorines everywhere and selectively removing or functionalizing them. Herein, we demonstrate a novel method to synthesize 1,4-cyclohexadienes through a dearomative photocatalytic C-C coupling reaction. This allows for access to materials that are orthogonal to the selectivity of the Birch reaction and are more functional-group-tolerant. The reaction also allows the efficient synthesis of polyfluorinated cannabinoids. While the yields are modest, the access to the new chemical space provided by the reaction is unprecedented by any means. The trifluorinated analog of THC, 1-deoxy-1,2,4-trifluoro-THC, is synthesized, demonstrating the importance of discovery chemistry and the ability to explore otherwise unknown structure-activity relationships.

Solubility of Iridium and Ruthenium Organometallic Photoredox Catalysts.

Despite the exponential growth of the field of photocatalysis, for reasons that are not entirely clear, these precious photocatalysts are often used in the literature at loadings that exceed their maximum solubility. On an industrial scale, the quantity of any precious metal catalyst can be a substantial financial burden or a sourcing issue, not to mention concerns as to the ecological and earth abundance of these catalysts. We believe that inattention to solubility has made these reactions appear less efficient than they actually are, because much of the photocatalyst remains undissolved. Therefore, the maximum solubilities of iridium and ruthenium centered photocatalysts have been systematically identified in industrially relevant solvents. Further, a literature photocatalytic reaction which our results suggested was beyond the maximum solubility has been revisited, with interesting results.

Visible Light Mediated Generation of trans-Arylcyclohexenes and Their Utilization in the Synthesis of Cyclic Bridged Ethers.

While accessible via UV-irradiation of cis-cyclohexene, trans-cyclohexene has thus far been an investigation driven by curiosity, and due primarily to its short lifespan, has until recently not been employed for productive synthesis. Herein, we present straightforward conditions that provide access to a class of trans-arylcyclohexenes and demonstrate their utility in the formation of oxabicyclic ethers, which are otherwise inaccessible from the corresponding cis-cyclohexene. A key challenge to utilizing the incredible ca. 52 kcal/mol strain energy of trans-cyclohexene to drive synthesis was overcoming its short lifetime. Herein, we show that preorganization via hydrogen bonding between the substrate and the reaction partner prior to isomerization is a viable strategy to overcome the inherently short lifetime of trans-cyclohexene.

Selective and Scalable Perfluoroarylation of Nitroalkanes.

Functionalized per- and polyfluoroarenes are important building blocks, with many industrially and medicinally important molecules containing them. Nucleophilic aromatic substitution can be employed as a quick and straightforward way to synthesize these building blocks. While many methods to derivatize fluoroarenes exist that use heteroatom centered nucleophiles, there are fewer methods that use carbon centered nucleophiles, and of those many are poorly defined. This work presents the SNAr reaction of nucleophiles generated from nitroalkanes with a variety of fluorinated arenes. Given that the products are versatile, accessing polyfluorinated arene building blocks in substantial scale is important. This method is highly regioselective, and produces good to moderate yields on a large scale, sans chromatography, and thus fulfills this need. In addition, the regioselectivity of the addition was probed using both DFT calculations and experimentally via halogen exchange.

Advances in Photocatalysis: A Microreview of Visible Light Mediated Ruthenium and Iridium Catalyzed Organic Transformations.

Photocatalytic organic transformations utilizing ruthenium and iridium complexes have garnered significant attention due to the access they provide to new synthetic spaces through new reaction mechanisms. A survey of the photophysical data and the diversity of transformations that may be accomplished utilizing commercially available photocatalysts is contained herein.