One-pot synthesis of pyrazoles through a four-step cascade sequence

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Heterocyclic Chemistry

Background:

• Pyrazoles are important heterocyclic compounds with diverse applications.
• Efficient synthesis of substituted pyrazoles remains a key challenge in organic chemistry.

Purpose of the Study:

• To develop a novel and efficient one-pot synthetic method for 3,4,5- and 1,3,5-pyrazoles.
• To explore the selective synthesis of different pyrazole isomers based on starting material substituents.

Main Methods:

• A four-step cascade reaction sequence was employed.
• Key steps include FeCl3-catalyzed propargylic substitution, aza-Meyer-Schuster rearrangement, base-mediated 6π electrocyclization, and thermal [1,5] sigmatropic shift.
• Tertiary propargylic alcohols and para-tolylsulfonohydrazide were used as starting materials.

Main Results:

• A one-pot synthesis of 3,4,5- and 1,3,5-pyrazoles was successfully achieved.
• The reaction demonstrated selectivity, yielding different pyrazole isomers based on the substituents of the starting alcohols.
• The cascade sequence efficiently constructs the pyrazole core.

Conclusions:

• The developed one-pot method offers an efficient route to substituted pyrazoles.
• This synthesis provides a valuable tool for accessing diverse pyrazole scaffolds.
• The regioselectivity is controllable by modifying the starting propargylic alcohols.