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Abstract An unprecedented Ag^I‐catalyzed efficient method for the coupling of imino ethers and enol diazoacetates through a [3+2]‐cycloaddition/C−O bond cleavage/[1,5]‐proton transfer cascade process is reported. The general class of imino ethers that includes oxazolines, benzoxazoles and benzimidates are applicable substrates for these reactions that provide direct access to fully substituted pyrroles with uniformly high chemo‐ and regioselectivity. High variability in substitution at the pyrrole 2‐, 5‐ and N‐positions characterizes this methodology that also presents an entry point for further pyrrole diversification via facile modification of resulting N‐functional pyrroles. 

Abstract 1,2,3‐Trisubstituted donor–acceptor cyclopropenes (DACPs) generated in situ from enoldiazo compounds react with nucleophiles to form α‐substituted succinic acid derivatives in high yields. Initial dirhodium(II) carboxylate catalysis rapidly converts enoldiazo‐acetates or ‐acetamides to DACPs that undergo catalyst‐free Favorskii ring opening with amines, and also with anilines, alcohols, and thiols, when facilitated by catalytic amounts of 4‐dimethylaminopyridine (DMAP). This methodology provides easy access to mixed esters and amides of monosubstituted succinic acids, including derivatives of naturally occurring compounds. It also affords dihydrazide, dihydroxamic acid, and diamide derivatives, as well as α‐substituted tetrahydropyridazine‐3,6‐diones in high yields. Attempts to generate optically enriched DACPs were not successful because their populations having theRandSconfigurations formed with a chiral dirhodium catalyst are quite similar, and the loss of enantiocontrol likely originates from the DACP ring forming step which is reversible with its intermediate metal carbene. 

Abstract The direct Friedel–Crafts‐type coupling and dedinitrogenation reactions of vinyldiazo compounds with aromatic compounds using a metal‐free strategy are described. This Brønsted acid catalyzed method is efficient for the formation of α‐diazo β‐carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or homoallylic carbocation species via vinyldiazo compounds. By choosing suitable nucleophilic reagents to selectively capture these intermediates, both trisubstituted α,β‐unsaturated esters, β‐indole‐substituted diazo esters, and dienes are obtained with good to high yields and selectivity. Experimental insights implicate a reaction mechanism involving the selective protonation of vinyldiazo compounds and the subsequent release of dinitrogen to form vinyl cations that undergo intramolecular 1,3‐ and 1,4‐ hydride transfer processes as well as fragmentation. 

Brønsted acid catalyzed formal [4 + 4]-, [4 + 3]-, and [4 + 2]-cycloadditions of donor–acceptor cyclobutenes, cyclopropenes, and siloxyalkynes with benzopyrylium ions are reported. [4 + 2]-cyclization/deMayo-type ring-extension cascade processes produce highly functionalized benzocyclooctatrienes, benzocycloheptatrienes, and 2-naphthols in good to excellent yields and selectivities. Moreover, the optical purity of reactant donor–acceptor cyclobutenes is fully retained during the cascade. The 1,3-dicarbonyl product framework of the reaction products provides opportunities for salen-type ligand syntheses and the construction of fused pyrazoles and isoxazoles that reveal a novel rotamer-diastereoisomerism. 

Chiral copper( i ) catalysts are preferred over chiral dirhodium( ii ) catalysts for [3 + 3]-cycloaddition reactions of γ-alkyl-substituted enoldiazoacetates compounds with nitrones. Using the In-SaBox ligand these reactions effectively produce cis -3,6-dihydro-1,2-oxazine derivatives under mild conditions in high yield and with exceptional stereocontrol, and enantioselectivity increases with the size of the γ-substituent. Mechanistic studies show that cycloaddition occurs solely through the formation of ( Z )-γ-substituted metallo-enolcarbene intermediates that are catalytically gennerated from both ( Z )- and ( E )-γ-substituted enoldiazoactates via donor–acceptor cyclopropene intermediates.