[3 + 2] Coupling of Quinone Monoacetals by Combined Acid–Hydrogen Bond Donor

Catalyst-Controlled Divergent Synthesis of 2H-Chromenes via [3 + 3] Annulation of Vinyl Sulfoxonium Ylides with Quinones

Herein, we report the synthesis of 2H-chromenes via catalyst-controlled highly regioselective [3 + 3] annulation of vinyl sulfoxonium ylides with quinones. Under boron-catalyzed conditions, the reaction between the ylide and quinone resulted in the formation of 2H-chromene-4-carboxylates. In contrast, a different mechanistic pathway was observed when utilizing a Ru(II) catalytic system, which led to the formation of 2H-chromene-2-carboxylates through a furan intermediate.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

[3 + 2] Coupling of Quinone Monoacetals with Vinyl Ethers Effected by Tetrabutylammonium Triflate: Regiocontrolled Synthesis of 2-Oxygenated Dihydrobenzofurans

The synthesis of 2-oxygenated dihydrobenzofurans involving the [3 + 2] coupling of quinone monoacetals with vinyl ethers has been realized by tetrabutylammonium triflate catalysis. The reaction involves a new activation method of the acetal moiety in quinone monoacetals under acid-free conditions affording the highly oxygenated dihydrobenzofurans. This new activation mode was achieved by using the triflate anion catalyst for stabilization of the highly reactive cationic intermediate.

Triflimide-Promoted Nucleophilic C-Arylation of Halopurines to Access N7-Substituted Purine Biaryls

Functionalized nucleobases are utilized in a wide range of fields; therefore, the development of new synthesis methods is essential for their continued application. With respect to the C⁶-arylation of halopurines, which possess a substituent at the N⁷-position, only a small number of successful cases have been reported, which is predominately a result of large steric hinderance effects. Herein, we report efficient and metal-free C⁶-arylations and S_NAr reactions of N⁷-substituted chloropurines in aromatic and heteroatom nucleophiles promoted by triflimide (Tf₂NH) in fluoroalcohol.

Catalyst-free synthesis of α,α-disubstituted carboxylic acid derivatives under ambient conditions via a Wolff rearrangement reaction

Herein, a hexafluoroisopropanol (HFIP)-promoted Wolff rearrangement reaction was developed, delivering various α,α-disubstituted carboxylic acid derivatives in good to excellent yields.

Exploiting hexafluoroisopropanol (HFIP) in Lewis and Brønsted acid-catalyzed reactions

Hexafluoroisopropanol (HFIP) is a solvent with unique properties that has recently gained attention for promoting a wide range of challenging chemical reactions. It was initially believed that HFIP was almost exclusively involved in the stabilization of cationic intermediates, owing to its high polarity and low nucleophilicity. However, in many cases, the mechanism of action of HFIP appears to be more complex. Recent findings reveal that many Lewis and Brønsted acid-catalyzed transformations conducted in HFIP additionally involve cooperation between the catalyst and HFIP hydrogen-bond clusters, akin to Lewis- or Brønsted acid-assisted-Brønsted acid catalysis. This feature article showcases the remarkable versatility of HFIP in Lewis and Brønsted acid-catalyzed reactions, with an emphasis on examples yielding mechanistic insight.

Nucleophilic Arylation of Halopurines Facilitated by Brønsted Acid in Fluoroalcohol

Various aryl-substituted purine derivatives were synthesized through the direct arylation of halopurines with aromatic compounds, facilitated by the combination of triflic acid and fluoroalcohol. This metal-free method is complementary to conventional coupling reactions using metal catalysts and reagents for the syntheses of aryl-substituted purine analogues.

A catalytic asymmetric one-pot [3+2] cyclization/semipinacol rearrangement sequence: an efficient construction of a multi-substituted 3H-spiro[benzofuran-2,1′-cyclopentane] skeleton

We report an asymmetric construction of multi-substituted 3H-spiro[benzofuran-2,1’-cyclopentane]s with three new stereocenters and two new ring systems.

NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations

In contrast to Nature that accomplishes polyene cyclizations seemingly with ease, such transformations are difficult to conduct in the lab. In our program dealing with the development of selective halogenations of alkenes, we now asserted that standard X⁺ reagents are perfectly suited for the biomimetic cation-π cyclization of both electron rich and poor linear polyenes in the presence of the Lewis base morpholine and the Lewis acid HFIP. The method stands out due to its broad substrate scope and practicability together with high chemical yields and excellent selectivities, even for highly challenging chloriranium-induced polyene cyclizations.

Catalytic asymmetric chemodivergent arylative dearomatization of tryptophols

The first catalytic asymmetric arylative dearomatization of tryptophols has been established. By using quinone imine ketals as aryl group surrogates and modulating the reaction conditions, the cascade reaction of tryptophols with quinone imine ketals afforded two series of arylative dearomatization products in generally high yields, and excellent diastereo- and enantioselectivities.

One-step formation of dihydrofuranoindoline cores promoted by a hypervalent iodine reagent

Treatment of aniline derivatives in the presence of a hypervalent iodine reagent and furan produces dihydrofuranoindoline cores in one step.

Ag(i)-catalyzed intramolecular transannulation of enynone tethered donor–acceptor cyclopropanes: a new synthesis of 2,3-dihydronaphtho[1,2-b]furans

An efficient AgOTf catalyzed tandem intramolecular transannulation of ((2-alkynyl)aryl)cyclopropyl ketones leading to the 2,3-dihydronaphtho[1,2-b]furans has been developed.

Synthesis of o-chlorophenols via an unexpected nucleophilic chlorination of quinone monoketals mediated by N,N'-dimethylhydrazine dihydrochloride

An unexpected nucleophilic chlorination of a quinone monoketal while carrying out a pyrazolidine synthesis has led to a general preparation of multisubstituted phenols. The products are obtained in good to high yields under mild conditions. The bridged pyrazolidines that were the original targets are obtained in the presence of a protic solvent.