Quinone-mediated hydrogen anode for non-aqueous reductive electrosynthesis.

Electrochemical synthesis can provide more sustainable routes to industrial chemicals1-3. Electrosynthetic oxidations may often be performed 'reagent-free', generating hydrogen (H2) derived from the substrate as the sole by-product at the counter electrode. Electrosynthetic reductions, however, require an external source of electrons. Sacrificial metal anodes are commonly used for small-scale applications4, but more sustainable options are needed at larger scale. Anodic water oxidation is an especially appealing option1,5,6, but many reductions require anhydrous, air-free reaction conditions. In such cases, H2 represents an ideal alternative, motivating the growing interest in the electrochemical hydrogen oxidation reaction (HOR) under non-aqueous conditions7-12. Here we report a mediated H2 anode that achieves indirect electrochemical oxidation of H2 by pairing thermal catalytic hydrogenation of an anthraquinone mediator with electrochemical oxidation of the anthrahydroquinone. This quinone-mediated H2 anode is used to support nickel-catalysed cross-electrophile coupling (XEC), a reaction class gaining widespread adoption in the pharmaceutical industry13-15. Initial validation of this method in small-scale batch reactions is followed by adaptation to a recirculating flow reactor that enables hectogram-scale synthesis of a pharmaceutical intermediate. The mediated H2 anode technology disclosed here offers a general strategy to support H2-driven electrosynthetic reductions.

Accessing Diverse Azole Carboxylic Acid Building Blocks via Mild C-H Carboxylation: Parallel, One-Pot Amide Couplings and Machine-Learning-Guided Substrate Scope Design.

This manuscript describes a mild, functional group tolerant, and metal-free C-H carboxylation that enables direct access to azole-2-carboxylic acids, followed by amide coupling in one pot. This demonstrates a significant expansion of the accessible chemical space of azole-2-amides, compared to previously known methodologies. Key to the described reactivity is the use of silyl triflate reagents, which serve as reaction mediators in C-H deprotonation and stabilizers of (otherwise unstable) azole carboxylic acid intermediates. A diverse azole substrate scope designed via machine-learning-guided analysis demonstrates the broad utility of the sequence. Density functional theory calculations provide detailed insights into the role of silyl triflates in the reaction mechanism. Transferrable applications of the protocol are successfully established: (i) A low pressure (CO2 balloon) option for synthesizing azole-2-carboxylic acids without the need for high-pressure equipment; (ii) the use of 13CO2 for the synthesis of labeled compounds; (iii) isocyanates as alternative electrophiles for direct C-H amidation; (iv) and the use of the developed chemistry in a 24 × 12 parallel synthesis workflow with a 90% library success rate. Fundamentally, the reported protocol expands the use of heterocycle C-H functionalization from late-stage functionalization applications toward its use in library synthesis. It provides general access to densely functionalized azole-2-carboxylic acid building blocks and demonstrates their one-pot diversification.

Calcium Dialkylamine Diazeniumdiolates: Synthesis, Stability, and Nitric Oxide Generation.

The therapeutic application of nitric oxide, an endogenous cellular signaling molecule, has been limited due to the difficulty of developing stable pro-drugs with slow kinetics of NO release. Diazeniumdiolates are valuable NO donors; however, synthetic challenges have hampered their use. O2-alkylation or arylation of diazeniumdiolates form stable pro-drugs which have found application in hypertension, cancer, and as antimicrobial agents. The synthesis of sodium diazeniumdiolates has proven to be challenging due to hazardous reaction conditions (high N2O concentrations, and flammable solvents), which can lead to detonation and suffered from limited scope. We have previously disclosed that synthesis of calcium diazeniumdiolate salts are a safer and more scalable alternative. Herein, we report the expanded scope of calcium diazeniumdiolates from benzylic amines, amides, and sterically bulky amines hitherto inaccessible and a comparison of their reactivity in comparison to sodium diazeniumdiolate.

Nine-Step Stereoselective Synthesis of Islatravir from Deoxyribose.

A stereoselective nine-step synthesis of the potent HIV nucleoside reverse transcriptase translocation inhibitor (NRTTI) islatravir (EfdA, MK-8591) from 2-deoxyribose is described. Key findings include a diastereodivergent addition of an acetylide nucleophile to an enolizable ketone, a chemoselective ozonolysis of a terminal olefin and a biocatalytic glycosylation cascade that uses a unique strategy of byproduct precipitation to drive an otherwise-reversible transformation forward.

Scalable Synthesis of Diazeniumdiolates: Application to the Preparation of MK-8150.

Synthetic diazeniumdiolate (DAZD)-based nitric oxide is utilized to modulate the nitric oxide (NO) concentration in cellular environments and to control physiological processes, yet chemists are still struggling to find efficient and scalable methodologies that will enable them to access sufficient quantities of the high-energy diazeniumdiolate intermediates for biological studies. Now, a general, scalable, safer, and high-yielding new methodology adaptable to the large-scale synthesis of DAZDs has been developed.

Enantioselective Synthesis of α-Methyl-ß-cyclopropyldihydrocinnamates.

α- and ß-substitution of dihydrocinnamates has been shown to increase the biological activity of various drug candidates. Recently, we identified enantio- and diastereopure α-methyl-ß-cyclopropyldihydrocinnamates to be important pharmacophores in one of our drug discovery programs and endeavored to devise an asymmetric hydrogenation strategy to improve access to this valuable framework. We used high throughput experimentation to define stereoconvergent Suzuki-Miyaura cross-coupling conditions affording (Z)-α-methyl-ß-cyclopropylcinnamates and subsequent ruthenium-catalyzed asymmetric hydrogenation conditions affording the desired products in excellent enantio- and diastereoselectivities. These conditions were executed on multigram to kilogram scale to provide three key enantiopure α-methyl-ß-cyclopropyldihydrocinnamates with high selectivity.

A practical synthesis of renin inhibitor MK-1597 (ACT-178882) via catalytic enantioselective hydrogenation and epimerization of piperidine intermediate.

A practical enantioselective synthesis of renin inhibitor MK-1597 (ACT-178882), a potential new treatment for hypertension, is described. The synthetic route provided MK-1597 in nine steps and 29% overall yield from commercially available p-cresol (7). The key features of this sequence include a catalytic asymmetric hydrogenation of a tetrasubstituted ene-ester, a highly efficient epimerization/saponification sequence of 4 which sets both stereocenters of the molecule, and a short synthesis of amine fragment 2.

Enantioselective hydrogenation of N-H imines.

N-H ketoimines 3a-3v are readily prepared in high yield via organometallic addition to nitriles and isolated as corresponding bench-stable hydrochloride salts. Homogeneous asymmetric hydrogenation of unprotected N-H ketoimines 3a-3v using Ir-(S,S)-f-binaphane as catalyst provides chiral amines 4a-4v in 90-95% yield with enantioselectivities up to 95% ee.