Au-catalyzed ring-opening reactions of 2-(1-alkynyl-cyclopropyl)pyridines with nucleophiles

Rh(II)-Catalyzed Alkynylcyclopropanation of Alkenes by Decarbenation of Alkynylcycloheptatrienes

Alkynylcyclopropanes have found promising applications in both organic synthesis and medicinal chemistry but remain rather underexplored due to the challenges associated with their preparation. We describe a convenient two-step methodology for the alkynylcyclopropanation of alkenes, based on the rhodium(II)-catalyzed decarbenation of 7-alkynyl cycloheptatrienes. The catalytic system employed circumvents a fundamental problem associated with these substrates, which usually evolve via 6-endo-dig cyclization or ring-contraction pathways under metal catalysis. This unique performance unlocks a rapid access to a diverse library of alkynylcyclopropanes (including derivatives of complex drug-like molecules), versatile intermediates that previously required much lengthier synthetic approaches. Combining experiments and DFT calculations, the complete mechanistic picture for the divergent reactivity of alkynylcycloheptatrienes under metal catalysis has been unveiled, rationalizing the unique selectivity displayed by rhodium(II) complexes.

Radical-based functionalization-oriented construction: rapid assembly of azaarene-substituted highly functionalized pyrroles

Totally different functionalization and construction as two fundamental synthetic protocols have long been applied to furnish azaarene variants. Here, a novel radical-based functionalization-oriented construction strategy by exploiting the electronic properties of azaarenes and the high reactivity of radicals is developed. Under a photoredox catalysis platform, the robust ability of such an artful combination of functionalization with construction is disclosed in the synthesis of valuable 3-azaarene-substituted densely functionalized pyrroles. In addition to the ability to use the readily accessible feedstocks, the high synthetic efficiency and the good functional group tolerance, the substrate scope is broad (81 examples) resulting from the capability to flexibly replace the types of azaarenes and other substituents. Control experiments and density functional theory (DFT) calculations elucidate the plausible mechanism involving the reaction pathways and the important role of NaH2PO4 as an additive in the reaction.

Gold(i)-catalyzed nucleophilic cyclization of β-monosubstituted o-(alkynyl)styrenes: a combined experimental and computational study

The diastereospecific 5-endo cyclization of β-monosubstituted o-(alkynyl)styrenes to 1-functionalized-1H-indenes is reported. The regiospecific generation of a cyclopropyl gold carbene intermediate is also supported by DFT calculations.

Efficient Gold(I) Acyclic Diaminocarbenes for the Synthesis of Propargylamines and Indolizines

Mononuclear gold(I) acyclic diaminocarbenes (ADCs) were prepared by the reaction of 1,2-cyclohexanediamine with the corresponding isocyanide complexes [AuCl(CNR)] (R = Cy, t Bu). The three-component coupling of aldehydes, amines, and alkynes was investigated by using these gold(I) ADC complexes. The new gold(I) metal complexes are highly efficient catalysts for the synthesis of propargylamines and indolizines in the absence of solvent and in mild conditions. This method affords the corresponding final products with excellent yields in short reaction times. Additionally, chiral gold(I) complexes with ADCs have been prepared and tried in the enantioselective synthesis of propargylamines.

Investigation of the Pyridinium Ylide--Alkyne Cycloaddition as a Fluorogenic Coupling Reaction

The cycloaddition of pyridinium ylides with alkynes was investigated under mild conditions. A series of 13 pyridinium salts was prepared by alkylation of 4-substituted pyridines. Their reactivity with propiolic ester or amide in various reaction conditions (different temperatures, solvents, added bases) was studied, and 11 indolizines, with three points of structural variation, were, thus, isolated and characterized. The highest yields were obtained when electron-withdrawing groups were present on both the pyridinium ylide, generated in situ from the corresponding pyridinium salt, and the alkyne (X, Z = ester, amide, CN, carbonyl, etc.). Electron-withdrawing substituents, lowering the acid dissociation constant (pKa) of the pyridinium salts, allow the cycloaddition to proceed at pH 7.5 in aqueous buffers at room temperature.

Synthesis of substituted indolizines via radical oxidative decarboxylative annulation of 2-(pyridin-2-yl)acetate derivatives with α,β-unsaturated carboxylic acids

A copper mediated radical oxidative annulation of 2-(pyridin-2-yl)acetate derivatives with α,β-unsaturated carboxylic acids is developed.

Recent advances in the synthesis of indolizines and their π-expanded analogues

Synthesis of indolizines developed during the last decade is reviewed, with special emphasis given to densely functionalized architectures, breakthrough strategies, compounds bearing electron-donating and electron-withdrawing substituents and π-expanded systems.

C3 functionalization of indolizines via In(iii)-catalyzed three-component reaction

Post-functionalization at the C3 position of indolizines via In(iii)-catalyzed three-component coupling reaction with amines and aldehydes allowed rapid access to a new class of indolizines with diverse functional groups at the C3 position in good to excellent yields.