Iridium-Catalyzed Reductive Deoxygenation of Esters for the Synthesis of Sterically Hindered Ethers.

The synthesis of sterically hindered α-tertiary and β-quaternary (neopentylic) ethers has long been constrained by the limitations of traditional S2 and related S1 approaches, namely low or inexistent reactivity arising from severe steric hindrance or competitive elimination/rearrangement pathways diverting the reaction outcome. Herein, we describe a general solution to the synthesis of sterically hindered ethers via an iridium-catalyzed reductive deoxygenation reaction of readily available ester and lactone starting materials. Employing commercially available, bench-stable IrCl(CO)(P[OCH(CF)]) as a precatalyst at 1 mol% loading with 4 equivalents of tetramethyldisiloxane (TMDS) as the terminal reductant at room temperature, this practical synthetic approach to hindered ethers features a simple, mix-and-stir, single-vessel protocol under ambient conditions and produces a diverse range of both acyclic and cyclic ether products in good to excellent yields.

Regiodivergent Photocatalytic Annulation for the Synthesis of gem-Difluorinated Cyclic Hydrocarbons.

Regiodivergent synthesis is a powerful strategy for expanding chemical space. Given the significance of fluorine-containing molecules in pharmaceutical sciences, a regiodivergent [3+2] cycloaddition of gem-difluorocyclopropyl urea to olefins and [1.1.

General Pyrrolidine Synthesis via Iridium-Catalyzed Reductive Azomethine Ylide Generation from Tertiary Amides and Lactams.

An iridium-catalyzed reductive generation of both stabilized and unstabilized azomethine ylides and their application to functionalized pyrrolidine synthesis via [3 + 2] dipolar cycloaddition reactions is described. Proceeding under mild reaction conditions from both amide and lactam precursors possessing a suitably positioned electron-withdrawing or a trimethylsilyl group, using 1 mol% Vaska's complex [IrCl(CO)(PPh)] and tetramethyldisiloxane (TMDS) as a terminal reductant, a broad range of (un)stabilized azomethine ylides were accessible. Subsequent regio- and diastereoselective, inter- and intramolecular dipolar cycloaddition reactions with variously substituted electron-deficient alkenes enabled ready and efficient access to structurally complex pyrrolidine architectures.

A General Iridium-Catalyzed Reductive Dienamine Synthesis Allows a Five-Step Synthesis of Catharanthine via the Elusive Dehydrosecodine.

A new reductive strategy for the stereo- and regioselective synthesis of functionalized isoquinuclidines has been developed. Pivoting on the chemoselective iridium(I)-catalyzed reductive activation of β,γ-unsaturated δ-lactams, the efficiently produced reactive dienamine intermediates readily undergo [4 + 2] cycloaddition reactions with a wide range of dienophiles, resulting in the formation of bridged bicyclic amine products. This new synthetic approach was extended to aliphatic starting materials, resulting in the efficient formation of cyclohexenamine products, and readily applied as the key step in the shortest (five-step) total synthesis of vinca alkaloid catharanthine to date, proceeding via its elusive biosynthetic precursor, dehydrosecodine.

Iridium-Catalyzed Aza-Spirocyclization of Indole-Tethered Amides: An Interrupted Pictet-Spengler Reaction.

A mild, reductive spirocyclization of indole-linked amides and lactams for the efficient and selective synthesis of aza-spirocyclic indoline products is described. The catalytic reductive activation of tertiary amides or lactams by Vaska's complex with tetramethyldisiloxane as the terminal reductant allowed iminium ion formation, before a diastereoselective 5-endo-trig spirocyclization of the tethered indole moiety was triggered. Terminal reduction affords the aza-spiroindoline products in an overall highly chemoselective and diastereoselective one-pot process.

Synergistic activities of macrolide antibiotics against Pseudomonas aeruginosa, Burkholderia cepacia, Stenotrophomonas maltophilia, and Alcaligenes xylosoxidans isolated from patients with cystic fibrosis.

Azithromycin and clarithromycin were paired with other antibiotics to test synergistic activity against 300 multidrug-resistant pathogens isolated from cystic fibrosis (CF) patients. Clarithromycin-tobramycin was most active against Pseudomonas aeruginosa and inhibited 58% of strains. Azithromycin-trimethoprim-sulfamethoxazole, azithromycin-ceftazidime, and azithromycin-doxycycline or azithromycin-trimethoprim-sulfamethoxazole inhibited 40, 20, and 22% of Stenotrophomonas maltophilia, Burkholderia cepacia complex, and Achromobacter (Alcaligenes) xylosoxidans strains, respectively.