Unexpected formation of bis-pyrazolyl derivatives by solid support coupledwith microwave irradiation

Starting from 1,3-dimethyl-5-aminopyrazole 1 and p-substituted benzaldehyde s 2 (R=H, CH3, NO2), four different compounds have been obtained: the Schif f bases 4, a bis-pyrazolyl Schiff base 6a (R=H), the expected bispyrazolo[3 ,4-b;4 ' ,3 ' -e]pyridine 7b (R=CH3) and the carbinol derived from the Schi ff base 8c (R=NO2). The products have been characterised by MS, NMR (H-1 an d C-13) and X-ray crystallography (in the case of 6a). A proposal for the r elationships between the different compounds and a possible mechanism is pr esented. (C) 2001 Elsevier Science Ltd. All rights reserved.