Synthesis of 5-hydroxy-Δ1-pyrrolines from aryl isoalkyl ketoximes and acetylene in a tuned superbase medium

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.

Synthesis of Pyrrolo[2,1-a]isoquinolinium Salts from 1-Pyrrolines and Alkynes via Rhodium-Catalyzed C-H Functionalization/N-Annulation Tandem Reaction

A convenient synthesis of pyrrolo[2,1-a]isoquinolinium salts from 1-pyrrolines and alkynes through rhodium-catalyzed C-H functionalization/N-annulation tandem reaction is described. The protocol features a good substrate tolerance, mild reaction conditions, and high yields of target products. Exploration of the alkyne scope unexpectedly revealed a novel labile functional group-promoted rhodium-catalyzed C-H functionalization/C-annulation/elimination cascade reaction of 1-pyrrolines with electron-deficient alkynes.

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity - more diversity

Expedient protocols for the synthesis of three types of highly functionalized azaheterocyclic scaffolds (dihydropyridazines, tetrahydropyridazines, and partially saturated tricyclic systems) from readily available hydroxypyrrolines and hydrazides are described. The directions of the transformation of a common initial intermediate, namely a Brønsted acid-activated hydroxypyrroline, depend on the reaction conditions and the structure of the hydrazides.

Acetylene in Organic Synthesis: Recent Progress and New Uses

Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and the construction of a number of functionalized molecules with different levels of molecular complexity were recently studied. Of particular importance is the utilization of acetylene in the synthesis of pharmaceutical substances and drugs. The increasing interest in acetylene and its involvement in organic transformations highlights a fascinating renaissance of this simplest alkyne molecule.

Transition-Metal-Free C-Vinylation of Ketones with Acetylenes: A Quantum-Chemical Rationalization of Similarities and Differences in Catalysis by Superbases MOH/DMSO and tBuOM/DMSO (M = Na, K)

Transition-metal-free C-vinylation of acetone with phenylacetylene catalyzed by superbases MOH/DMSO and tBuOM/DMSO (M = Na, K) has been theoretically evaluated in the B3LYP/6-311++G**//B3LYP/6-31+G* approach to rationalize similarities and differences in activity of the above catalytic systems. The close solvate surroundings of sodium and potassium tert-butoxides have been studied. Formation of tBuOM· nDMSO complexes and their structure and thermodynamic stability are discussed in comparison with similar complexes of alkali-metal hydroxides MOH· nDMSO. Activation barriers of the title reaction in the presence of tBuOM· nDMSO complexes are found to be less than those with MOH· nDMSO complexes participating.

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.