Facile Route to Tetrasubstituted Pyrazoles Utilizing Ceric Ammonium Nitrate

Abstract

A convenient approach for the synthesis of tetrasubstituted pyrazoles is described. The method involves the treatment of 1,3-diketones and allyltrimethylsilane with CAN followed by cerium-catalyzed addition of substituted hydrazines to construct pyrazoles in good yields.

Base-free two-step synthesis of 1,3-diketones and β-ketoesters from α-diazocarbonyl compounds, trialkylboranes, and aromatic aldehydes

“…In reactions with the free hydrazines 7a-b (Table 3), we employed ceric ammonium nitrate (CAN), which was recently reported to improve yields in this transformation. 14 The reaction with the unsymmetrical diketone 6b produced the expected 1 : 1 (determined by 1 H NMR) mixture of regioisomeric pyrazoles 8a, (Table 3, entry 1). However, when symmetrical diketones 6a,c-f were employed, several symmetrical tetrasubstituted pyrazoles 8a-f were obtained in moderate to excellent yields (Table 3, entries 2-7).…”