Chiral Auxiliary Approach for Gold(I)‐Catalyzed Cyclizations

Abstract

Two different classes of stereoselective cyclizations have been developed using a chiral auxiliary approach with commercially available [JohnPhosAu(MeCN)SbF6] as catalyst. First, a stereoselective cascade cyclization of 1,5‐enynes was achieved using the Oppolzer camphorsultam as chiral auxiliary. In this case, a one‐pot cyclization‐hydrolysis sequence was developed to directly afford enantioenriched spirocyclic ketones. Then, the stereoselective alkoxycyclization of 1,6‐enynes was mediated by an Evans‐type oxazolidinone. A reduction‐hydrolysis sequence was selected to remove the auxiliary to give enantioenriched b‐tetralones. DFT studies confirmed that the steric clash between the chiral auxiliary and alkene accounts for the experimentally observed diastereoselective cyclization through the Si face.

Azobenzene-Integrated NHC Ligands: A Versatile Platform for Visible-Light-Switchable Metal Catalysis

“…More specifically, protodeauration, the reaction of an organogold complex (LAuR) with a Bro̷nsted acid (X–H), plays a central role in gold catalysis by simultaneously releasing both the product (R–H) and the catalyst (LAuX). Numerous studies have highlighted this formal acid–base reaction as a critical elementary step, indicating its potential as a key control lever for regulating catalytic reactivity. − …”

Microporous Polymeric Networks Containing a Long-Term Stable AuI Catalyst for Enyne Cyclization

“…Looking at a specific field of catalysis, in the last 2 decades, Au I complexes have emerged as exceptional catalytic materials − for the activation of alkynes , and, in particular, enynes, − which has permitted the obtainment of a wide variety of cyclic products used in synthetic chemistry as starting compounds . Au I complexes, of the [AuXL] type, are usually used for these reactions, which in the presence of a Ag salt, acting as a halide extractor, leads to the formation of a naked gold [AuL] + that acts as a very soft and active electrophile.…”

Fluorinated Biphenyl Phosphine Ligands for Accelerated [Au(I)]-Catalysis

“…Interestingly, in the case of PedroPhos (Scheme , results reported in red), the energy of all intermediates is lowered by 4.0 ± 0.7 kcal/mol, suggesting a more efficient catalysis as well as stabilizing action toward the involved organo-gold species. With respect to its chemospecificity 3 vs 3 ′, an even greater energy difference between the two competing protodeauration transition states TS 6 – 3 and TS 7 – 3 ′ (16.1 kcal/mol for JohnPhosAu vs 17.3 kcal/mol for PedroPhos Au) is observed, thus strongly suggesting that the final protodeauration step is the key to account for the overall chemoselectivity …”