2-Ethoxy-5-(4-methylpiperazinyl-l-sulfonyi)benzaldehyde was prepd. from salicylaidehyde and directly cyclocondensed (1: 1 by moles) with 4-amino-1-methyl-3-n-propylpirazolo-5-carboxyamide (9) in dimethylamide as solvent and with Na2S2O5 as condensing agent at 110 degrees C for 3 hrs. to yield sildenafil in > 80%. Pfizer's (EP 0463 756 (1990)) route to, and the mode and mechanism of action of sildenafil are reviewed.