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A mechanistic study on a direct arylation using a native picolylamine directing group is reported. Kinetic studies determined the concentration dependence of substrates and catalysts, as well as catalyst degradation, which led to the development of a new set of reaction conditions capable of affording a robust kinetic profile. During reaction optimization, a small impurity was observed, which was determined to be a dual C-H activation product. A second set of conditions were found to flip the selectivity of the C-H activation to form this tetracycle in high yield. A catalytic cycle is proposed for the intermolecular/intramolecular C-H activation pathway.

Generation of reactive intermediates and interception of these fleeting species under physiological conditions is a common strategy employed by Nature to build molecular complexity. However, selective formation of these species under mild conditions using classical synthetic techniques is an outstanding challenge. Here, we demonstrate the utility of biocatalysis in generating o-quinone methide intermediates with precise chemoselectivity under mild, aqueous conditions. Specifically, α-ketoglutarate-dependent non-heme iron enzymes, CitB and ClaD, are employed to selectively modify benzylic C-H bonds of o-cresol substrates. In this transformation, biocatalytic hydroxylation of a benzylic C-H bond affords a benzylic alcohol product which, under the aqueous reaction conditions, is in equilibrium with the corresponding o-quinone methide. o-Quinone methide interception by a nucleophile or a dienophile allows for one-pot conversion of benzylic C-H bonds into C-C, C-N, C-O, and C-S bonds in chemoenzymatic cascades on preparative scale. The chemoselectivity and mild nature of this platform is showcased here by the selective modification of peptides and chemoenzymatic synthesis of the chroman natural product (-)-xyloketal D.

A new Au(I)-catalyzed method for the preparation of trisubstituted indolizines from easily accessible 2-propargyloxy-pyridines is reported. The reaction tolerates a wide range of functionality, allowing for diversity to be introduced in four distinct regions of the product (R, R

N-Alkyl 2-pyridones and other enolizable heterocycles are important synthetic constructs, due to their prevalence in natural products and pharmaceutical targets and their capacity to serve as models for a number of biological and chemical processes. The disclosed Au(I)-catalyzed reaction utilizes 2-propargyloxypyridines to access N-alkylated 2-pyridone products derived from both 5-exo and 6-endo addition of the nitrogen to the pendent alkyne. Experimental and computational studies suggest that the desired 5-exo N-alkenyl 2-pyridonyl ethers are formed reversibly in the transformation. After extensive optimization, biaryl Au(I) catalyst 21 was found to overcome the inherent preference for the 6-endo pathway and provide the highest combination of 5-exo selectivity and yield. Herein, we report the application of this new Au(I)-catalyzed C-N bond formation to the preparation of a variety of N-alkenyl 2-pyridonyl ether analogues, which have the potential to serve as an entry point for the synthesis of complex N-alkyl 2-pyridone-containing frameworks.