Room Temperature ICl-Induced Dehydration/Iodination of 1-Acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles. A Selective Route to Substituted 1-Acyl-4-iodo-1H-pyrazoles

Abstract

A number of new functionally substituted 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles have been prepared in moderate to excellent yields from the corresponding 2-alkyn-1-ones. The resulting dihydropyrazoles undergo dehydration and iodination in the presence of ICl and Li2CO3 at room temperature to provide 1-acyl-4-iodo-1H-pyrazoles.

Synthesis of Some 2-(3-Alkyl/aryl-5-trifluoromethylpyrazol-1-yl)-4-(coumarin-3-yl)thiazoles as Novel Antibacterial Agents

“…and ICl (3 equiv.). [44] To the best of our knowledge this is the first report describing the dehydration of hydroxyl pyrazoline with such a mild base like sodium carbonate (0.5 equiv.) in absolute EtOH with excellent yields, thus providing a greener and efficient protocol with reduced number of steps for such type of reactions.…”

One-pot activation–alkynylation–cyclization synthesis of 1,5-diacyl-5-hydroxypyrazolines in a consecutive three-component fashion

“…1-Acyl-5-hydroxypyrazolines have been shown to be analgesics with a slightly improved pain-relieving efficacy than Aspirin ® [24–25], and 5-nitro-2-furyl-substituted derivatives are active antibacterials against the strains S. aureus , A. aerogenes , E. coli and B. subtilis (Fig. 2) [26–27].…”

Intramolecular CH Oxidative N‐Allylation of C‐Homoallylhydrazones to 5‐Vinyl‐2‐pyrazolines Catalyzed by the [Pd(OAc)2]/BIMINAP System

“…This method, based on a Michael addition process, remains the most widely used,6 and the same principle applies to a recently disclosed asymmetric version based on an acid‐catalyzed cycloisomerization of α,β‐unsaturated hydrazones 7. Nevertheless, alternative [2+3] processes have been devised for the synthesis of 2‐pyrazolines with specific substitution patterns from hydrazine equivalents and other three carbon electrophiles, such as homopropargylic alcohols,8 ynones (giving hydrated pyrazoles),9 1,3‐dihaloalkanes (through concomitant oxidation of the primary pyrazolidine product),10 or 2‐acylaziridines 11. Although 5‐carbonyl, 5‐cyano, and 5‐aryl‐2‐pyrazolines have been extensively studied,1 only a few vinyl‐substituted pyrazolines have been prepared, for example by [3+2] cycloaddition of diazoalkanes with Fischer carbene analogues of acrylic CC double bonds 12…”