Chemo- and Regioselective 1,3-Dipolar Cycloaddition of 2-Diazopropane over 1,4-Benzoquinone: Synthesis of New Pyrazoloquinones

Abstract

1,3-Dipolar cycloaddition reaction of 2-diazopropane 1 with 1,4-benzoquinone 2 carried out at −20 °C led to a minor mono-cycloadduct 4 and mixture of bis-cycloadducts 6 and 7. The same addition realized with 3H-pyrazole 7 at −60 °C for 2 h yields a mixture of compounds 8 and 9 and results in O-alkylation. The reaction of 3H-pyrazoles 4 and 7 with dimethylsulfoxide and oxalyl chloride under Swern conditions led to pyrazolenines 11 and 12.

GRAPHICAL ABSTRACT

Keywords:

• 1,3-Dipolar cycloaddition
• pyrazoloquinone
• regiochemistry
• Swern oxidation