Gold-Catalyzed Cycloaromatization of 2,4-Dien-6-yne Carboxylic Acids: Synthesis of 2,3-Disubstituted Phenols and Unsymmetrical Bi- and Terphenyls

Gold(I)-Catalyzed Intermolecular Formal [4+2] Cycloaddition of O-Aryl Ynol Ethers and Enol Ethers: Synthesis of Chromene Derivatives

Gold(I)-catalyzed formal [4+2] cycloaddition of O-aryl ynol ethers 1 and enol ethers 2 is described. This intermolecular reaction between two electron-rich unsaturated systems takes place, under mild conditions, in the presence of 5 mol% [IPrAu(CH3 CN)]SbF6 as catalyst giving chromene derivatives with good yields. The cycloaddition is completely regio- and stereoselective, as well as versatile for both reactives. Silyl enol ethers can also react in the same way and under the same reaction conditions with quantitative yields. A plausible mechanism through a selective addition of the enol ether to the alkyne gold activated complex followed by an intramolecular aromatic electrophilic substitution is proposed. Several experimental results support the presence of a cationic oxonium intermediate prior to the aromatic substitution. The reaction represents a new entry to the chromene core.

Gold-Catalyzed Addition of Carboxylic Acids to Alkynes and Allenes: Valuable Tools for Organic Synthesis

In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the initial cycloisomerization of an alkynoic acid are also discussed.

Temperature-controlled sequential Suzuki-Miyaura reactions for preparing unsymmetrical terphenyls

A one-pot protocol of double Suzuki-Miyaura reactions has been developed for the synthesis of unsymmetrical terphenyls. In the absence of a ligand, potassium bromophenyltrifluoroborate reacts with arylboronic acid and then sequentially with a hetero/aryl bromide by controlling the reaction temperature, providing unsymmetrical p- and m-terphenyl compounds in moderate to good overall yields. This protocol provides a convenient and practical approach to unsymmetrical terphenyls under ligand-free and aerobic conditions.

Total synthesis of complex terpenoids employing radical cascade processes

Covering: 2011-2017Radical cyclizations have a rich history in organic chemistry and have been particularly generous to the field of natural product synthesis. Owing to their ability to operate in highly congested molecular quarters, and with significant functional group compatibility, these transformations have enabled the synthesis of numerous polycyclic terpenoid natural products over the past several decades. Moreover, when programmed accordingly into a synthetic plan, radical cascade processes can be used to rapidly assemble molecular complexity, much in the same way nature rapidly constructs terpene frameworks through cationic cyclization pathways. This review highlights recent total syntheses of complex terpenoids (from 2011-2017) employing C-C bond-forming radical cascade sequences.

One-pot construction of sterically challenging and diverse polyarylphenols via transition-metal-free benzannulation and their potent in vitro antioxidant activity

One pot novel synthesis of highly functionalized polyarylphenols via benzannulation under transition-metal-free conditions and their antioxidant activities are described.

1,3-Dien-5-ynes: Versatile Building Blocks for the Synthesis of Carbo- and Heterocycles

1,3-Dien-5-ynes have been extensively used as starting materials for the synthesis of a wide number of different carbo- and heterocycles. The aim of this review is to give an overview of their utility in organic synthesis, highlighting the variety of compounds that can be directly accessed from single reactions over these systems. Thus, cycloaromatization processes are initially commented, followed by reactions directed toward the syntheses of five-membered rings, other carbocycles and, finally, heterocycles. The diverse methodologies that have been developed for the synthesis of each of these types of compounds from 1,3-dien-5-ynes are presented, emphasizing the influence of the reaction conditions and the use of additional reagents in the outcome of the transformations.

(Hetero)aromatics from dienynes, enediynes and enyne–allenes

Recent advances in the synthesis of (hetero)aromatics starting from polyenes, such as dienynes, enediynes and enyne–allenes, are discussed.

PtI2-catalyzed cyclization of 3-acyloxy-1,5-enynes with the elimination of HOAc and a benzyl shift: synthesis of unsymmetrical m-terphenyls

A new cyclization of 1,5-enyne was developed to synthesize the m-terphenyls via the elimination of HOAc and a benzyl shift.

An advanced and novel one-pot synthetic method for diverse benzo[c]chromen-6-ones by transition-metal free mild base-promoted domino reactions of substituted 2-hydroxychalcones with β-ketoesters and its application to polysubstituted terphenyls

Novel one-pot syntheses of a variety of benzo[c]chromen-6-one derivatives were accomplished by Cs₂CO₃-promoted reactions of 2-hydroxychalcones.

Synthesis of 6-substituted salicylates via biomimetic aromatization utilizing the cross metathesis of a vinyl dioxinone with homoallylic alcohols

We herein report biomimetic syntheses of 6-substituted salicylates from the cross metathesis of 2,2-dimethyl-6-vinyl-1,3-dioxin-4-one with homoallylic alcohols, oxidation, and aromatization of the intermediate enone–dioxinones. Of particular note is the use of the catalyst 1,4-diazabicyclo[2.2.2]octane in the microwave thermolytic ketene generation and trapping, cyclization, and dehydration reaction sequence.

Recent advances in the gold-catalyzed additions to C-C multiple bonds

C-O, C-N and C-C bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of C-C multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of X-H (X = O, N, C) bonds to C-C multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present.