Utility of chloroacetonitrile in construction of some hitherto novel pyrazole and thiazole derivatives

2-(-Piperidin-1-yl) acetamide (2) was easily prepared by reacting chloroacetonitrile with piperidine. Furthermore, (2) was allowed to react with different aromatic aldehydes to afford novel arylidene derivatives (3a,b). Unexpectedly, 2-oxo-4-hydroxy-thiazole (5) was obtained instead of 2-(piperidin-1-yl-methylene) thiazolidin-4-one (4) when (2) was treated with mercaptoacetic acid under fusion conditions. Subsequent treatment of (5) with aromatic aldehydes and either malononitrile or cyanoacetamide (1:1:1 molar ratios) produced the hitherto unknown pyrano[2,3-d] thiazole derivatives (6a,b) and (7). Novel pyrazole derivatives (8a, b) and (9) were synthesized upon cyclocondensation of (2) with aromatic aldehydes and hydrazine hydrate. Unfortunately, attempts to prepare novel isoxazole derivatives by utilizing hydroxylamine instead of hydrazine hydrate following the previous procedure were failed. Surprisingly, the uncyclized products (10a,b) were obtained rather than 3-hydroxy-4-piperidinyl-isoxazole (11a,b). Upon refluxing thiosemicarbazide with (2) and aromatic aldehydes under the same conditions, pyrazolinone carbothioamides (12), (13) and (14a-c) were obtained.