Abstract
Ring-closing metathesis as a key step to construct 2,6-dihydropyrano[2,3-c]pyrazole ring system
Highlights
The pyrano[2,3-c]pyrazole ring system (Fig. 1, A) is present in a wide variety of biologically active compounds.[1]
We describe a method for the construction of the 2,6-dihydropyrano[2,3-c]pyrazole ring system (Fig. 1, E) via a ring-closing metathesis (RCM) reaction
The synthetic strategy designed to construct the 2,6-dihydropyrano[2,3-c]pyrazole ring system employs a diene substrate that contains an ethene unit attached to an allyloxy unit onto the pyrazole core, which can participate in the RCM reaction (Scheme 1)
Summary
The pyrano[2,3-c]pyrazole ring system (Fig. 1, A) is present in a wide variety of biologically active compounds.[1]. We describe a method for the construction of the 2,6-dihydropyrano[2,3-c]pyrazole ring system (Fig. 1, E) via a ring-closing metathesis (RCM) reaction. The O-allylation of 1a with allyl bromide in the presence of NaH gave O-allylated pyrazole 2a.31 To introduce a formyl group at the 4-position of the pyrazole ring, we employed a previously reported procedure based on the Vilsmeier-Haack reaction.[32] Heating compound 2a with POCl3 in N,N-dimethylformamide (DMF) at 60 °C resulted in the formation of the desired pyrazole-4-carbaldehyde 3a in 91% yield (Scheme 1).
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