3H-Pyrroles from ketoximes and acetylene: synthesis, stability and quantum-chemical insight

Diastereoselective synthesis of tetrahydropyrrolo[1,2-d]oxadiazoles from functionalized Δ1-pyrrolines and in situ generated nitrile oxides

Tetrahydropyrrolo[1,2-d]oxadiazoles have been synthesized in good-to-excellent yields via the cycloaddition of nitrile oxides (in situ generated from aldoximes) to readily accessible functionalized Δ¹-pyrrolines. The reaction proceeds smoothly at room temperature in a two-phase system in the presence of sodium hypochloride as an oxidant to diastereoselectively afford pharmaceutically prospective 1,2,4-oxadiazolines fused with a five-membered ring. The reaction tolerates a broad range of substrates, including those with oxidant-sensitive functional groups and competitive reaction sites.

Modular approach to non-aromatic and aromatic pyrroles through gold-catalyzed [3 + 2] cycloaddition of 2H-azirines and ynamides

The developed modular approach to hard-to-reach non-aromatic 3H- and 2H-pyrroles is based on the integration of 2H-azirines and ynamides.

The Elusive Paal-Knorr Intermediates in the Trofimov Synthesis of Pyrroles: Experimental and Theoretical Studies

We have used isoxazolo[3,4-b]pyridin-3(1H)-one and isoxazolo[3,4-b]quinolin-3(1H)-one as "masked" heterocyclic hydroxylamines to generate Paal-Knorr intermediates of the Trofimov pyrrole synthesis. The previously inaccessible intermediates, trapped by ethyl propiolate, were obtained by reacting corresponding isoxazolones with 4-fold excess of ethyl propiolate under basic conditions at ambient temperature, and characterized by means of IR and NMR spectroscopic data as well as by single crystal X-ray analysis. Quantum chemical calculations of a [3,3]sigmatropic rearrangement of the N,O-divinyl hydroxylamines to corresponding imino-aldehydes (Paal-Knorr intermediates) revealed that this reaction proceeds via chairlike transition state and is exothermic.

From Heteroaromatic Acids and Imines to Azaspirocycles: Stereoselective Synthesis and 3D Shape Analysis

Heteroaromatic carboxylic acids have been directly coupled with imines using propylphosphonic anhydride (T3P) and NEt(iPr)2 to form azaspirocycles via intermediate N-acyliminium ions. Spirocyclic indolenines (3H-indoles), azaindolenines, 2H-pyrroles and 3H-pyrroles were all accessed using this metal-free approach. The reactions typically proceed with high diastereoselectivity and 3D shape analysis confirms that the products formed occupy areas of chemical space that are under-represented in existing drugs and high throughput screening libraries.