gem-Difluoro-Masked o-Quinone Methides Generated by Photocatalytic Radical (3+3) Annulation and Their (4+1) Cycloaddition with Sulfur Ylides

Scandium Triflate Catalyzed Cycloadditions of Vinyl Diazo Compounds and In Situ Formed Naphthoquinone Methides

Vinyl diazo carbonyl compounds have received great attention and are widely employed in the cycloadditions of in situ formed reactive intermediates. Metal carbenes are predominantly involved in cycloadditions, and transformations of vinyl diazo compounds that do not proceed via the metal carbene pathway have been seldom reported. Herein, scandium-catalyzed cycloadditions of vinyl diazo compounds and in situ formed 2-naphthoquinone-8-methides are achieved, and naphthalene-fused polycyclic products were obtained in up to 88% yield. In the transformation, the nucleophilic conjugate addition of vinyl diazo compounds to in situ formed 2-naphthoquinone-8-methides generates vinyl diazonium intermediates, which undergo an intramolecular Friedel-Crafts reaction and intramolecular transesterification to yield the final product.

Photoinduced Formal Cross-[3+3] Cycloaddition of Vinyldiazo Reagents with Acceptor-Only Diazoalkanes

In this study, we devised an innovative approach for the synthesis of pyrazine derivatives through a photoinduced formal cross-[3+3] cycloaddition between vinyldiazo reagents and acceptor-only diazoalkanes. This method leverages the differential reactivity of two distinct diazo compounds: vinyldiazo reagents, which upon visible light irradiation form key cyclopropane intermediates, and acceptor-only diazoalkanes, which function as 1,3-dipoles to capture the photogenerated reactive species. The reactions proceed exclusively under visible light, yielding 1,4-dihydropyridazines with a broad substrate scope and compatibility with various functional groups. Importantly, the synthesized 1,4-dihydropyridazines can be readily converted to other valuable products. The mechanism, elucidated through UV-vis absorption studies, deuterium labeling experiments, control experiments, and in situ NMR spectroscopy, provides a clear understanding of the observed reactivity.

Blue light-induced diazo cross-coupling: synthesis of allyldiazo compounds through reshuffling of functionalities

In this paper, we describe a new type of cross-coupling between simple diazo and vinyldiazo compounds that gives access to unusual allyldiazo products. Blue light discriminates two diazo compounds towards free carbene formation, triggering sequential cyclopropenation, (3+2) cycloaddition and ring opening rearrangement processes. This strategy involves an overall reshuffle of diazo functionality and olefinic carbons of vinyldiazo compounds with an extrusion of nitrogen. Mechanistic studies including a 15N-labelling experiment demonstrate that the diazo functionality of allyldiazo products derives from simple diazo compounds, while vinyldiazo reagents are selectively decomposed via energy transfer with thioxanthone photocatalyst. The obtained allyldiazo compounds can be efficiently converted into synthetically useful structures such as 1,3-dienes, gem-difluoro-1,4-diene, hydrazine, dihydropyrazole, pyridazine, and bicyclobutane.

o-Quinone methides in natural product synthesis: an update

In recent years, ortho-quinone methides have emerged as indispensable reactive species for enhancing synthetic efficiency in accessing various bioactive natural products. Importantly, the emulation of nature's patterns and strategies has yielded numerous refined synthetic pathways for the construction of intricate molecules. o-Quinone methides (o-QMs) have demonstrated remarkable versatility in organic synthesis, especially in strategies guided by biomimetic logic. This review aims to delve into bio-inspired strategies employed over the past five years in the total synthesis of natural products involving ortho-quinone methides.

Lewis-Acid-Catalyzed Diastereoselective [4 + 2] Cycloaddition of Vinyldiazo Compounds with N-Acyliminium Cations

An FeCl3-catalyzed [4 + 2] cycloaddition of vinyldiazo compounds with N-acyliminium cations generated from 3-hydroxyisoindolinones is described. A series of diazo-containing isoindolo[2,1-a]quinolinones were constructed in good yields with excellent diastereoselectivities, including those with three contiguous stereogenic centers. The resultant products were readily converted into various isoindolo[2,1-a]quinolinone derivatives based on the rich chemistry of the remaining diazo functionality.

Radical 1,3-Hydrosulfonylation of Vinyldiazo Compounds with Sulfinyl Sulfones

Sulfinyl sulfones, as high-valence sulfurization reagents, are widely used to assemble sulfur sources on carbon skeletons, such as one-, two-, and four-carbon synthons, to access organosulfur compounds. However, their reaction with three-carbon synthons has remained a mystery until now. We report here a radical 1,3-hydrosulfonylation of vinyldiazo compounds with sulfinyl sulfones. This reaction not only represents the first example of the reaction of sulfinyl sulfones with three-carbon synthons but also opens up the application of vinyldiazo compounds in radical monofunctionalization.

Photocatalytic (3 + 3) Annnulation of Vinyldiazo Compounds and Aminocyclopropanes

A (3 + 3) annulation of aminocyclopropanes and vinyldiazo compounds enabled by organo-photocatalysis is described. The reaction allows the regioselective synthesis of cyclohexenes bearing adjacent amino and carbonyl groups with broad functional group tolerance. In a departure from previous reports, our work demonstrated that a distonic radical cation can be preferentially intercepted by weakly nucleophilic vinyldiazo compounds, followed by an exclusive 6-endo radical cyclization for ring closure. Based on the interaction between adjacent amino and ester groups, the products can be further converted to cyclohexene-fused 1,3-oxazinane and azetidine.