Enantioselective and Regiodivergent Gold and Chiral Brønsted Acid Catalyzed Cycloisomerization/Diels-Alder Reaction of 1,10-Dien-4-yn-3-yl Acetates: Synthesis of Norbornene-Embedded Tricarbocycles.

A synthetic method for the enantioselective and regiodivergent synthesis of hexahydro-2H-2,4a-methanonaphthalen-4-yl and octahydro-2,4-methanoazulen-1-yl esters that relies on the gold(I)- and chiral Brønsted acid-catalyzed cycloisomerization/Diels-Alder (CDA) reaction of (E)-1,10-dien-4-yn-3-yl acetates is described.

Recent Advances in the Gold-Catalyzed Reactions of Propargyl Esters.

ConspectusLate-transition-metal-based complexes represent an indispensable catalytic tool in chemical synthesis due to their ability to increase molecular complexity rapidly and efficiently from readily accessible substrates in a single operation. Added to this is the exquisite control of product chemo-, diastereo-, enantio-, and site-selectivities achieved by catalytic systems of the transition-metal salts that have been developed to mediate a wide range of functional group transformations. Within this venerable synthetic toolbox, complexes and salts of Au(I) and Au(III) have emerged in recent years as an invaluable addition as a result of their potent σ- and π-Lewis acidities and ability to stabilize cationic reaction intermediates. The insights provided by mechanistic studies examining the various electronic, steric, and stereoelectronic factors at play in the organogold species that are expected to be formed in the catalytic chemistry of the transition-metal complex have also been pivotal in understanding and exploring their potential synthetic utility. Illustrative of this, for example, is the contribution made by the gold-catalyzed cycloisomerization chemistry of propargyl esters in synthetic strategies to a variety of bioactive natural products and compounds of current pharmaceutical and materials interest. This Account summarizes our efforts over the past decade toward realizing new single-step strategies for carbocyclic and heterocyclic synthesis that relied on the gold-catalyzed reactions of propargyl esters. It outlines synthetic methods developed by the group that exploited the unique reactivities of the gold-carbene species typically generated from the [2,3]-sigmatropic rearrangement of the compound class containing a terminal or electron-deficient alkyne moiety on exposure to the transition-metal salt. This Account also describes the realization of synthetic methods initiated by the gold-catalyzed 1,3-acyloxy migration of propargyl esters with an electronically unbiased disubstituted C≡C bond that delivers the corresponding allenyl ester that is primed for further reactivity on activation by the group 11 metal complex. The studies formed a part of an ongoing overarching program within our group that was focused on determining reactivities in gold catalysis that would enable their application as readily recognizable disconnections in retrosynthetic analysis. They were additionally a part of efforts aimed at evaluating the opportunities offered by the relativistic effects possessed by a Au(I) and Au(III) complex, the most pronounced among the d-block elements and thus the catalyst of choice in alkyne activation chemistry, to generate new chemical space. For instance, we demonstrated in several studies the cycloisomerization of 1,3- and 1,4-enyne esters to be a reliable strategy for the in situ formation of a wide range of 1,4-cyclopentadienyl derivatives. Their further reaction with an appropriately placed functional group or a second starting material was then shown to afford a variety of synthetic targets containing the five-membered ring structure. An example of this was the assembly of a new member of the 1H-isoindole compound family that was found to exhibit potent TNF-α (tumor necrosis factor-α) inhibitor activity.

Copper(I)-catalysed site-selective C(sp3)-H bond chlorination of ketones, (E)-enones and alkylbenzenes by dichloramine-T.

Strategies that enable intermolecular site-selective C-H bond functionalisation of organic molecules provide one of the cornerstones of modern chemical synthesis. In chloroalkane synthesis, such methods for intermolecular site-selective aliphatic C-H bond chlorination have, however, remained conspicuously rare. Here, we present a copper(I)-catalysed synthetic method for the efficient site-selective C(sp3)-H bond chlorination of ketones, (E)-enones and alkylbenzenes by dichloramine-T at room temperature. A key feature of the broad substrate scope is tolerance to unsaturation, which would normally pose an immense challenge in chemoselective aliphatic C-H bond functionalisation. By unlocking dichloramine-T's potential as a chlorine radical atom source, the product site-selectivities achieved are among the most selective in alkane functionalisation and should find widespread utility in chemical synthesis. This is exemplified by the late-stage site-selective modification of a number of natural products and bioactive compounds, and gram-scale preparation and formal synthesis of two drug molecules.