Synthesis of Amides and Nitriles from Vinyl Azides and p-Quinone Methides

A Three-Component Synthesis of Spiropyrrolines

A rapid synthesis of medicinally important spiropyrrolines has been achieved by the reaction of 1,3-indanediones, benzaldehyde, and (1-azidovinyl)benzene under catalyst- and reagent-free conditions. This is the first report to synthesize diverse spiropyrroline compounds from readily available feedstock materials under metal-free conditions.

BF3 ⋅Et2 O-Catalyzed Selective C-4 Alkylation of Isoquinolin-1(2H)-ones Employing p-Quinone Methides

The direct C-4 alkylation of isoquinolin-1(2H)-one moiety is a challenging transformation in organic synthesis. Here we present a practical and efficient synthesis of C-4 alkylated isoquinolin-1(2H)-ones through conjugate addition of isoquinolin-1(2H)-ones to p-quinone methides for the first time. The process is facilitated by Lewis acid catalysis and this operationally straightforward, mild, metal-free and one-pot transformation provides a wide range of C-4 alkylated isoquinolin-1(2H)-ones at ambient temperature in good to excellent yields.

Addition of sulfonylphthalides to para-quinone methides: Selective 1,6-additions and oxidative annulations

KO^tBu mediated addition of sulfonylphthalides to p-quinone methides led to the selective synthesis of isochroman-1,4-diones and addition products. Interestingly, isochroman-1,4-diones were obtained via an unprecedented oxidative annulation pathway. The present work highlights a wide variety of substrates, good yields, shorter reaction time and ambient reaction conditions. Furthermore, a few addition products were transformed into functionalized heterocyclic molecules. Additionally, the scale-up experiment suggests the practical feasibility of preparing isochroman-1,4-diones in higher-scale reactions.

Vinyl azides in organic synthesis: an overview

Among organic azides, vinyl azides have attracted significant attention, because of their unique properties in organic synthesis, which led to reports of many types of research on this versatile conjugated azide in recent years. This magical precursor can also be converted into intermediates such as iminyl radicals, 2H-azirines, iminyl metal complexes, nitrilium ions, and iminyl ions, making this compound useful in heterocycle synthesis.

Iridium-Catalyzed Enantioselective and Chemodivergent Allenylic Alkylation of Vinyl Azides for the Synthesis of α-Allenylic Amides and Ketones

The first enantioselective synthesis of α-allenylic amides and ketones through allenylic alkylation of vinyl azides is reported. In these chemodivergent reactions, cooperatively catalyzed by a Ir^I /(phosphoramidite,olefin) complex and Sc(OTf)₃ , vinyl azides act as the surrogate for both amide enolates and ketone enolates. The desiccant (molecular sieves) plays a crucial role in controlling the chemodivergency of this enantioconvergent and regioselective reaction: Under otherwise identical reaction conditions, the presence of the desiccant led to α-allenylic amides, while its absence resulted in α-allenylic ketones. Utilizing racemic allenylic alcohols as the alkylating agent, the overall process represents a dynamic kinetic asymmetric transformation (DyKAT), where both the products are formed with the same absolute configuration. To the best of our knowledge, this is the first example of the use of vinyl azide as the ketone enolate surrogate in an enantioselective transformation.

1,6-Addition of 1,2,3-NH triazoles to para-quinone methides: Facile access to highly selective N1 and N2 substituted triazoles

The regioselective syntheses of N¹ and N² substituted triazoles through a 1,6-addition reaction of 1,2,3-NH triazoles to p-quinone methide were achieved under mild reaction conditions. The present reactions showed superior results in terms of selectivity, mild reaction conditions, short reaction time and broad substrate scope with good functional-group compatibility. Considering the high synthetic value of N¹- and N²-substituted compounds and p-QM related research, the present strategy will greatly benefit researchers in various fields.

Silver-Catalyzed Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines and Phenols

A simple and efficient method for the silver-catalyzed regioselective 1,6-hydroarylation of para-quinone methides (p-QMs) with anilines and phenols has been established. Without the need for pre-protection, a broad range of...

Synthesis of 2-monosubstituted indolin-3-ones by cine-substitution of 3-azido-2-methoxyindolines

We report herein the formal cine-substitution/hydrolysis of 3-azidoindole intermediates generated from 3-azido-2-methoxyindolines (AZINs). This protocol enables the introduction of both various carboxylic acid and alcohol into indolin-3-ones at the C2-position,...

Vinyl Azides as Radical Acceptors in the Vitamin B12-Catalyzed Synthesis of Unsymmetrical Ketones

Vinyl azides are very reactive species and as such are useful building blocks, in particular, in the synthesis of N-heterocycles. They can also serve as precursors of ketones. These form in reactions of vinyl azides with nucleophiles or radicals. We have found, however, that under light irradiation vitamin B12 catalyzes the reaction of vinyl azides with electrophiles to afford unsymmetrical carbonyl compounds in decent yields. Mechanistic studies revealed that alkyl radicals are key intermediates in this transformation.

Silver-Catalyzed Regioselective Phosphorylation of para-Quinone Methides with P(III)-Nucleophiles

A simple and efficient method for the silver-catalyzed regioselective phosphorylation of para-quinone methides (p-QMs) with P(III)-nucleophiles (P(OR)₃, ArP(OR)₂, Ar₂P-OR) has been established via Michaelis-Arbuzov-type reaction. A broad range of P(III)-nucleophiles and para-quinone methides are well tolerated under the mild conditions, giving the expected diarylmethyl-substituted organophosphorus compounds with good to excellent yields. Moreover, a series of corresponding enantiomers can be obtained by employing dialkyl arylphosphonite (ArP(OR)₂) as substrates. The control experiments and ³¹P NMR tracking experiments were also performed to gain insights for the plausible reaction mechanism. This protocol may have significant implications for the formation of C(sp³)-P bonds in Michaelis-Arbuzov-type reactions.

An aryl thiol-vinyl azide coupling reaction and a thiol-vinyl azide coupling/cyclization cascade: efficient synthesis of β-ketosulfides and arene-fused 5-methylene-2-pyrrolidinone derivatives

The addition reaction of thiol to vinyl azide has been extensively studied. Variously substituted aryl thiols are all viable for this coupling process. The scope of the other partner is successfully expanded from α-aryl vinyl azide to α-alkyl vinyl azide. A thiol-vinyl azide coupling/cyclization cascade is realized with substituted aryl vinyl azides carrying a 2-methoxycarbonyl group. The value of β-ketosulfide products was demonstrated by its application in S-heterocycle synthesis.

Hf(OTf)4-Catalyzed 1,6-Conjugate Addition of 2-Alkyl-azaarenes to para-Quinone Methides

Herein we reported a Hf(OTf)₄-catalyzed carbon-carbon bond formation reaction between 2-alkyl-azaarenes and para-quinone methides (p-QMs). This 1,6-conjugate addition protocol offered rapid access to a large array of triarylethane products in good yields. The catalyst loading could be reduced to 1 mol %. Studies pertinent to scale-up reaction and product derivatization were also presented.

Metal-Free, Acid/Phosphine-Induced Regioselective Thiolation of p-Quinone Methides with Sodium Aryl/Alkyl Sulfinates

A simple and efficient method for the regioselective thiolation of p-quinone methides with sodium aryl/alkyl sulfinates has been established using an acid/phosphine-induced radical route under transition-metal-free conditions. A broad range of sodium aryl/alkyl sulfinates and p-quinone methides (p-QMs) are compatible for the reaction, giving the expected products with good to excellent yields. Control experiments were also performed to gain insights into the generation mechanism of thiyl radicals and hydrogen-atom transfer process. This protocol provides a safe and feasible way for the formation of carbon-sulfur bonds.

Iridium-Catalyzed Enantioselective α-Allylic Alkylation of Amides Using Vinyl Azide as Amide Enolate Surrogate

Among the unstabilized enolates used as nucleophiles in iridium-catalyzed asymmetric allylic alkylation reactions, amide enolates are the least explored. Vinyl azides are now employed as amide enolate surrogates in Ir-catalyzed asymmetric allylic alkylation with branched allylic alcohols as the allylic electrophile. Competing reaction pathways are suppressed through the systematic tuning of the steric and electronic properties of vinyl azide to effect the α-allylic alkylation of secondary acetamides with high atom economy, exclusive branched selectivity, and mostly excellent enantioselectivity.

A bench-stable low-molecular-weight vinyl azide surrogate for a cascade reaction: facile access to novel N-vinyl-1,2,3-triazoles

A novel metal-catalyzed cascade reaction of stable low-molecular-weight vinyl azide surrogate with S-/O-nucleophiles and alkynes was disclosed in a general fashion, thus providing mild and efficient access to various N-vinyl-1,2,3-triazoles bearing new functional groups.

InCl3-catalyzed 5-exo-dig cyclization/1,6-conjugate addition of N-propargylamides with p-QMs to construct oxazole derivatives

An InCl₃-catalyzed tandem intramolecular 5-exo-dig cyclization/1,6-conjugate addition/aromatization of N-propargylamides with p-QMs to produce oxazoles tethering diarylmethane has been successfully developed.

BF3·OEt2-Catalyzed Vinyl Azide Addition to in Situ Generated N-Acyl Iminium Salts: Synthesis of 3-Oxoisoindoline-1-acetamides

BF₃·OEt₂-catalyzed nucleophilic addition of vinyl azides to in situ generated N-acyl iminium salts obtained from 3-hydroxyisoindolinones is described in this article. The procedure is operationally simple, mild, additive, and metal-free. The reaction proceeds smoothly at ambient temperature with a wide range of 3-hydroxyisoindol-1-ones and vinyl azides to afford 3-oxoisoindoline-1-acetamides (32 examples) in high yields (up to 97%). Furthermore, the synthetic utility of this methodology is depicted by exploiting the reactivity of an amide functionality in the products.

Silver-mediated three-component cycloaddition reaction for direct synthesis of 1-N-vinyl-substituted 1,2,3-triazoles

Herein, we report direct synthesis of 1-N-vinyl-1,2,3-triazoles via silver-mediated three-component cycloaddition reaction of phenylacetylenes, trimethylsilylazide, and 1,3-dicarbonyl compounds. The synthetic protocol proceeds with operational simplicity, good substrate and functional group compatibility, and easily available feedstocks, and without the need for pre-installation of vinylazide precursors, and offers a practical method for the efficient elaboration of triazole derivatives.

Radical cyanomethylation via vinyl azide cascade-fragmentation

Herein, a novel methodology for radical cyanomethylation is described. The process is initiated by radical addition to the vinyl azide reagent 3-azido-2-methylbut-3-en-2-ol which triggers a cascade-fragmentation mechanism driven by the loss of dinitrogen and the stabilised 2-hydroxypropyl radical, ultimately effecting cyanomethylation. Cyanomethyl groups can be efficiently introduced into a range of substrates via trapping of α-carbonyl, heterobenzylic, alkyl, sulfonyl and aryl radicals, generated from a variety of functional groups under both photoredox catalysis and non-catalytic conditions. The value of this approach is exemplified by the late-stage cyanomethylation of pharmaceuticals.

Mn-Catalyzed 1,6-conjugate addition/aromatization of para-quinone methides

A series of ferrocenyl triazole ligands have been synthesized and characterized, which proved to be effective for the Mn-catalyzed 1,6-conjugate addition/aromatization of para-quinone methides with good to high yields under mild conditions. This protocol provided an efficient and practical route to the synthetically interesting functionalized quinones, methines and their analogues.

Copper-catalyzed regioselective cyclization of vinyl azides by gem-difluoromethylene for trisubstituted pyridines

A novel copper-catalyzed cyclization of readily available vinyl azides with gem-difluoromethylene is described.

Interruption of Formal Schmidt Rearrangement/Hosomi-Sakurai Reaction of Vinyl Azides with Allyl/Propargylsilanes

An interrupted Schmidt rearrangement/Hosomi-Sakurai reaction of N-tosyl and S-substituted vinyl azides is reported. With BF₃·Et₂O as a Lewis acid promoter, the denitrogenative fragmentation of vinyl azides facilitates the generation of the N/ S-stabilized carbocations, which further undergo nucleophilic addition by allyl/propargylsilanes for C-C bond formation. As a result, a variety of homoallylic/allenylic amines can be afforded in good yields under mild reaction conditions with well-defined functional-group tolerance.

Intramolecular Schmidt Reaction of Vinyl Azides with Cyclic Ketones

Cyclic ketones tethered with a vinyl azide group undergo a Schmidt-hydrolysis sequence to give secondary lactams bearing a ketone side chain. Secondary lactams are obtained in a regioselective manner that is not possible in a conventional Schimdt reaction. In addition to the well-documented C-2 nucleophilicity, the N nucleophilicity of vinyl azide disclosed in this work opens a new direction for reaction invention involving vinyl azides.

1,4-Conjugate addition/esterification of ortho-quinone methides in a multicomponent reaction

A novel 1,4-conjugate addition/esterification of ortho-quinone methides in a multicomponent reaction has been developed for facilely accessing 3,3-diarylpropanamides.

Enantioselective Synthesis of Functionalized 4-Aryl Hydrocoumarins and 4-Aryl Hydroquinolin-2-ones via Intramolecular Vinylogous Rauhut-Currier Reaction of para-Quinone Methides

A novel strategy for the asymmetric construction of functionalized 4-aryl-3,4-dihydrocoumarins and 4-aryl-3,4-dihydroquinolin-2-ones via an intramolecular vinylogous Rauhut-Currier reaction of para-quinone methides (p-QMs) under the bifunctional catalysis of chiral amine-phosphine is described. This intramolecular mode for the catalytic enantioselective 1,6-conjugate addition of p-QMs has been explored for the first time, delivering two types of synthetically important heterocycles in high yields and enantioselectivites.

α-Substituted vinyl azides: an emerging functionalized alkene

Vinyl azides are highly versatile synthons that provide access to numerous N-heterocycles and other functional groups.