Synthesis and chemistry of N‐arylated pyrano[2,3‐c]pyrazoles

Abstract

Novel N2-arylated pyrano[2,3-c]pyrazol-6-ones 2 can be prepared in a selective manner by generating the anion of 1 (R=H) with lithium hexamethyldisilazide in DMF and quenching with activated aryl halides. Sterically demanding groups such as phenyl as in 5 reduce reactivity significantly while electronwithdrawing substituents such as trifluoromethyl and phenyl at C4 of the pyranone ring as in 10 and 15 render the pyranone carbonyl particularly susceptible to attack by nucleophiles resulting in ring-opening to give novel crotonyl derivatives. Proof of structure required a variety of nmr methods involving proton, carbon, and nitrogen nuclei.

3,4-Dimethyl-1-phenylpyrano[2,3-c]pyrazol-6(1H)-one

“…Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON. (Khan et al, 1982, Samaritoni et al, 2007. It has been shown that these contain analgesic and anti-inflammatory activities (Kuo et al, 1984, Abdallah & Zaki, 1999) and while others are tested for their antiplatelet activity (Huang et al, 1992).…”

“…For a related structure, see: Ramsay & Steel (1985). For background to the pyrano[2,3-c]pyrazol-6-one ring system, see: Abdallah & Zaki (1999); Huang et al (1992); Khan et al (1982); Kuo et al (1984); Ramsay & Steel (1985); Samaritoni et al (2007). For graph-set notation, see: Bernstein et al (1995).…”