Potassium tert-Amylate: A Cautionary Tale.

Potassium tert-amylate ( t-AmylOK) is a well-known, commercially available base and generally regarded as a more solvent-soluble form of potassium tert-butoxide ( t-BuOK). However, despite the structural similarity between the tert-butyl and amyl moieties, potassium tert-amylate in toluene can undergo distinct physical property changes in the presence of protic solvents that warrant further consideration. This is particularly surprising given that t-AmylOH is a byproduct of deprotonation with t-AmylOK, as well as the fact that its structurally similar relative, t-BuOK, is commercially available in t-BuOH.

The palladium-catalyzed aerobic kinetic resolution of secondary alcohols: reaction development, scope, and applications.

The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

Kinetic Modeling of the Nickel-Catalyzed Esterification of Amides.

Nickel-catalyzed coupling reactions provide exciting tools in chemical synthesis. However, most methodologies in this area require high catalyst loadings, which commonly range from 10-20 mol % nickel. Through an academic-industrial collaboration, we demonstrate that kinetic modeling can be used strategically to overcome this problem, specifically within the context of the Ni-catalyzed conversion of amides to esters. The successful application of this methodology to a multigram-scale coupling, using only 0.4 mol % Ni, highlights the impact of this endeavor.

Heterogeneous reductive isomerization reaction using catalytic Pd/C and H2.

[reaction: see text] A highly selective catalytic reductive isomerization reaction is described. The extremely mild and neutral reaction conditions (10% Pd/C, H2, and MeOH at 0 degrees C) tolerate a wide range of functional groups and generally result in excellent yields. Mechanistic studies suggest that this reaction does not proceed via a stepwise reduction/elimination sequence or a pi-allylpalladium intermediate.

Discovery of ABT-267, a pan-genotypic inhibitor of HCV NS5A.

We describe here N-phenylpyrrolidine-based inhibitors of HCV NS5A with excellent potency, metabolic stability, and pharmacokinetics. Compounds with 2S,5S stereochemistry at the pyrrolidine ring provided improved genotype 1 (GT1) potency compared to the 2R,5R analogues. Furthermore, the attachment of substituents at the 4-position of the central N-phenyl group resulted in compounds with improved potency. Substitution with tert-butyl, as in compound 38 (ABT-267), provided compounds with low-picomolar EC50 values and superior pharmacokinetics. It was discovered that compound 38 was a pan-genotypic HCV inhibitor, with an EC50 range of 1.7-19.3 pM against GT1a, -1b, -2a, -2b, -3a, -4a, and -5a and 366 pM against GT6a. Compound 38 decreased HCV RNA up to 3.10 log10 IU/mL during 3-day monotherapy in treatment-naive HCV GT1-infected subjects and is currently in phase 3 clinical trials in combination with an NS3 protease inhibitor with ritonavir (r) (ABT-450/r) and an NS5B non-nucleoside polymerase inhibitor (ABT-333), with and without ribavirin.

Development of an enantiodivergent strategy for the total synthesis of (+)- and (-)-dragmacidin f from a single enantiomer of quinic Acid.

An enantiodivergent strategy for the total chemical synthesis of both (+)- and (-)-dragmacidin F beginning from a single enantiomer of quinic acid has been developed and successfully implemented. Although unique, the synthetic routes to these antipodes share a number of key features, including novel reductive isomerization reactions, Pd(II)-mediated oxidative carbocyclization reactions, halogen-selective Suzuki couplings, and high-yielding late-stage Neber rearrangements.

The total synthesis of (+)-dragmacidin F.

The first total synthesis of (+)-dragmacidin F has been accomplished, establishing the absolute configuration of this biologically important, antiviral marine alkaloid. The convergent route described features a palladium-mediated oxidative pyrrole carbocylization reaction to construct the [3.3.1] bicycle, as well as a highly selective Suzuki coupling to build the carbon skeleton of the natural product. A late-stage Neber rearrangement allows for the facile installation of the aminoimidazole moiety to provide (+)-dragmacidin F.