Diastereospecific Gold(I)-Catalyzed Cyclization Cascade for the Controlled Preparation of N- and N,O-Heterocycles

Advancements in Gold-Catalyzed Cascade Reactions to Access Carbocycles and Heterocycles: An Overview

This review summarizes recent developments (from 2006 to 2022) in numerous important and efficient carbo- and heterocycle generations using gold-catalyzed cascade protocols. Herein, methodologies involve selectivity, cost-effectiveness, and ease of product formation being controlled by the ligand as well as the counter anion, catalyst, substrate, and reaction conditions. Gold-catalyzed cascade reactions covered different strategies through the compilation of various approaches such as cyclization, hydroarylation, intermolecular and intramolecular cascade reactions, etc. This entitled reaction is also useful for the synthesis of spiro, fused, bridged carbo- and heterocycles.

Assembling Complex Structures through Cascade and Cycloaddition Processes via Non-Acceptor Gold or Rhodium Carbenes

The ability of highly energetic metal–carbene intermediates to engage in complex cascade or formal cycloaddition processes is one of the most powerful tools for building intricate molecular architectures in a straightforward manner. Among this type of organometallic intermediates, non-acceptor metal carbenes are particularly challenging to access and, therefore, have experienced slower development. In this regard, our group has exploited the use of electrophilic gold(I) complexes to selectively activate certain classes of substrates for the generation of this type of intermediate. Thus, very different types of molecules, such as enynes or 7-substituted cycloheptatrienes, lead to the formation of carbenes under gold(I) catalysis. Related rhodium(II) carbenes can also be generated from cycloheptatrienes. In this account, we aim to summarize our efforts towards the in situ generation of such highly versatile organometallic species as well as studies on their reactivity through formal cycloadditions or complex cascade reactions.

1 Introduction

2 Generation of Au(I)-Vinylcarbenes via a Cycloisomerization/1,5-Alkoxy Migration Cascade

2.1 Intramolecular Trapping of Au(I) Vinylcarbenes

2.1.1 Applications in Total Synthesis

2.2 Intermolecular Trapping of Au(I) Vinylcarbenes

2.2.1 Total Synthesis of Schisanwilsonene A

2.2.2 Trapping with Furans, 1,3-Dicarbonyl Compounds and Cyclic Alkenes

2.2.3 Mechanism of the Cycloisomerization/1,5-Migration Sequence and the Role of the OR Migrating Group

2.2.4 (4+3) Cycloadditions from Enynes

3 Formal Cycloadditions of Simple Donor Metal Carbenes

3.1 The Metal-Catalyzed Retro-Buchner Reaction

3.2 Formal Cycloadditions with Non-Acceptor Carbenes via Metal-Catalyzed Aromative Decarbenations

3.2.1 (4+1) Cycloadditions of Au(I) Carbenes

3.2.2 (3+2) Cycloadditions of Au(I) Carbenes

3.2.3 (4+3) Cycloadditions of Rh(II) Carbenes

4 Concluding Remarks

Understanding the reaction mechanism of gold-catalyzed reactions of 2,1-benzisoxazoles with propiolates and ynamides

The detailed reaction mechanisms of gold-catalyzed reactions of 2,1-benzisoxazoles with propiolates and ynamides have been investigated with the aid of density functional theory calculations.

(Z)-Trifluoromethyl-Trisubstituted Alkenes or Isoxazolines: Divergent Pathways from the Same Allene

Because of a charge-dipole interaction involving nonbonding electron pairs on fluorine, protonation of trifluoromethyl allenes leads to tri- or tetrasubstituted alkenes with high (Z)-selectivity. Treatment of the same allenes with catalytic Au(I) initiates a reaction cascade that produces isoxazolines in high yield.

Gold Catalysed 1,4-Enyne Acetate Strategy for the Synthesis of 1H-Indenes and Partially Hydrogenated Methanonaphtho[1,2-c]furan-1,3(4H)-diones

A synthetic method to prepare 1H-indenes and partially hydrogenated methanonaphtho[1,2-c]furan-1,3(4H)-diones from gold(i)-catalysed 1,4-enyne acetate cycloisomerisation and oxidation or Diels–Alder reaction with maleic anhydride is described. The proposed mechanism involves Rautenstrauch rearrangement of the 1,4-enyne motif to give an insitu formed 1,3-cyclopentadiene intermediate. This is followed by 6-endo-dig cyclisation of the cyclic adduct and oxidation to give the aromatic carbocycle or Diels–Alder reaction with maleic anhydride to afford the bridged furan product.

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

Gold is currently one of the most used metals in organometallic catalysis. The ability of gold to activate unsaturated groups in different modes, together with its tolerance to a wide range of functional groups and reaction conditions, turns gold-based complexes into efficient and highly sought after catalysts. Natural products and relevant compounds with biological and pharmaceutical activity are often characterized by complex molecular structures. (Cyclo)isomerization reactions are often a useful strategy for the generation of this molecular complexity from synthetically accessible reactants. In this review, we collect the most recent contributions in which gold(I)- and/or gold(III)-catalysts mediate intramolecular (cyclo)isomerization transformations of unsaturated species, which commonly feature allene or alkyne motifs, and organize them depending on the substrate and the reaction type.

Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones

A synthetic method to prepare 1-naphthyl ketones from gold(i)-catalysed oxidative cycloisomerisation of 1,6-diyne acetates is described. The proposed mechanism involves cyclopropenation–cycloreversion of the 1,6-diyne motif initiated by a 1,2-acyloxy migration. This is followed by nucleophilic attack of the ensuing gold carbenoid species by a molecule of water and autoxidation to give the aromatic product.