Gold(I)-catalyzed enantioselective synthesis of benzopyrans via rearrangement of allylic oxonium intermediates

Phosphoramidite gold(I)-catalyzed diastereo- and enantioselective synthesis of 3,4-substituted pyrrolidines

In this article the utility of phosphoramidite ligands in enantioselective Au(I) catalysis was explored in the development of highly diastereo- and enantioselective Au(I)-catalyzed cycloadditions of allenenes. A Au(I)-catalyzed synthesis of 3,4-disubstituted pyrrolidines and γ-lactams is described. This reaction proceeds through the enantioselective Au(I)-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (-)-isocynometrine.

Gold(I)-catalyzed diastereo- and enantioselective 1,3-dipolar cycloaddition and Mannich reactions of azlactones

Azlactones participate in stereoselective reactions with electron-deficient alkenes and N-sulfonyl aldimines to give products of 1,3-dipolar cycloaddition and Mannich addition reactions, respectively. Both of these reactions proceed with good to excellent diastereo- and enantioselectivity using a single class of gold catalysts, namely C(2)-symmetric bis(phosphinegold(I) carboxylate) complexes. The development of the azlactone Mannich reaction to provide fully protected anti-α,β-diamino acid derivatives is described. 1,3-Dipolar cycloaddition reactions of several acyclic 1,2-disubstituted alkenes and the chemistry of the resultant cycloadducts are examined to probe the stereochemical course of this reaction. Reaction kinetics and tandem mass spectrometry studies of both the cycloaddition and Mannich reactions are reported. These studies support a mechanism in which the gold complexes catalyze addition reactions through nucleophile activation rather than the more typical activation of the electrophilic reaction component.

Enantioselective gold-catalyzed functionalization of unreactive sp3 C-H bonds through a redox-neutral domino reaction

Selectivity is golden: The first asymmetric redox-neutral domino reaction catalyzed by gold that results in the direct functionalization of unreactive sp(3) C-H bonds has been reported. This method consists of a heterocyclization/1,5-hydride transfer/cyclization reaction and provides synthetically valuable azepines with high enantioselectivities and in high yields (Tf = triflate; see scheme).

Weinreb amides in carbene chemistry: a time-resolved IR investigation into a potential intramolecular stabilization mechanism

A chloromethylhydroxamiccarbene was generated photochemically in an attempt to form an intramolecularly stabilized carbene. A rapidly formed intermediate at 1645 cm(-1) decayed with an observed rate of 1.99 × 10(6) s(-1). Other intermediates were also observed. These also decayed, albeit much more slowly (k(obs) = 3.47 × 10(3) and 1.98 × 10(4) s(-1)). Multiple intermediates are apparently a function of both the proximal N,O-dimethylhydroxamic ester and multiple conformers of both the carbene and precursor.

Gold(I)-catalyzed enantioselective polycyclization reactions

A series of enantioselective polycyclization reactions, catalyzed by a cationic bisphosphine gold complexes, are described. The polycyclization reactions, which employ an alkyne as an initiating group, begin with a gold-promoted 6-exo-dig cyclization and can be terminated with a variety of nucleophiles including carboxylic acids, phenols, sulfonamides, and electron-rich aryl groups. This method allows for the preparation of up to four bonds in a single operation with excellent diastereo- and enantioselectivity.

A Reactivity-Driven Approach to the Discovery and Development of Gold-Catalyzed Organic Reactions

Approaches to research in organic chemistry are as numerous as the reactions they describe. In this account, we describe our reactivity-based approach. Using our work in the area of gold-catalysis as a background, we discuss how a focus on reaction mechanism and reactivity paradigms can lead to the rapid discovery of new synthetic tools.

Gold(I)-catalyzed enantioselective [4 + 2]-cycloaddition of allene-dienes

An enantioselective gold(I)-catalyzed intramolecular [4 + 2]-cycloaddition of allenes and dienes is reported. The reactions allow for the asymmetric synthesis of trans-hexahydroindenes and pyrrolidine products using C(3)-symmetric phosphitegold(I) and ortho-arylphosphoramiditegold(I) complexes as catalysts, respectively.