1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene (TBD) Triggered Diastereoselective [3+2] Cycloaddition of Azomethine Imines and Pyrazoleamides

Abstract

A practical and mild approach to prepare tetrahydropyrazolo[1,2-a]-pyrazole-1,7-diones, bearing up to three stereocentres, by reacting ready available N,N'-cyclic azomethine imines and pyrazoleamides under catalytic loading of commercial 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), has been developed. The products are obtained in good yields and high diastereoselectivity, working at room temperature. Preliminary bioassay showed the products to inhibit growth of Gram-positive bacteria.

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

“…They can be successfully employed as alternative reagents under milder reaction conditions and then easily elaborated to afford common carbonyl compounds or other derivatives . Inspired by the pivotal work of Yamamoto ,, and Mukaiyama on the reactivity of nitrosobenzene in aldol-type reactions and prompted by our interest in synthetic applications of carboxylic acid surrogates, we sought to develop a methodology for α-imination of relatively α-acidic N -acyl pyrazoles. We speculated that N -acyl pyrazoles treated with nitrosoarenes under basic conditions would undergo a base-catalyzed N -nitroso aldol reaction followed by dehydration to give unprecedented α-imino N -acyl pyrazoles suitable for further functionalizations (Scheme e).…”

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

“…The reaction products were separated by column chromatography and their structures proved by spectral data. Because there are contradictory data on the product structures of the reaction of DABCH with chalcones in the literature [ 11 , 13 ], we have carried out the careful structure analysis of the obtained compounds. So, in the 1 H NMR spectrum of compound 3a there are only two signals for the substituted pyrazolidine ring – a doublet (2H) at 4.48 ppm ( J = 7.4 Hz) and a triplet (1H) at 4.39 ppm ( J = 7.4 Hz).…”

Nitrone/Imine Selectivity Switch in Base‐Catalysed Reaction of Aryl Acetic Acid Esters with Nitrosoarenes: Joint Experimental and Computational Study

“…Intrigued by this observation, we questioned whether a similar approach could be applied to access ketonitrones, by reacting easily available aryl acetic acid esters, which are notoriously less acidic at the αposition than the corresponding acyl pyrazoles (Scheme 1 D). [19] This would open a direct and convenient route to ketonitrones, alternative to route B (iii) (Scheme 1). Moreover, we investigated the issues affecting the nitrone/imine selectivity and the overall mechanistic framework, by means of experimental and computational studies, to pursue a better understanding of the Ehrlich-Sachs type reaction, useful for further applications.…”

“…High chemical selectivity toward imines observed, although traces of nitrones were occasionally detected, when using compounds less prone to enolate formation. Intrigued by this observation, we questioned whether a similar approach could be applied to access ketonitrones, by reacting easily available aryl acetic acid esters, which are notoriously less acidic at the α‐position than the corresponding acyl pyrazoles (Scheme 1 D) [19] . This would open a direct and convenient route to ketonitrones, alternative to route B(iii) (Scheme 1).…”