Activation of Acyl Groups by Oxadiazoline and Thiadiazoline Derivatives

Abstract

New acylation reagents, 4-acetyl-2-phenyl-1, 3, 4-oxa- and thia-diazolin-5-ones and -thiones [6 a-d], prepared by the reaction of 2-phenyl-1, 3, 4-oxa- and thia-diazolin-5-ones and -thiones [5 a-d] with acetic anhydride in reasonable yields, were allowed to react with various amines at room temperature to give the corresponding amides quantitatively. The aminolyses of [6 a-d] by cyclohexylamine indicated that [6 a-d] are 10²-10⁷ times more reactive than p- nitrophenyl acetate, and thiadiazolines [6 c, d] are 4-50 times more reactive than corresponding oxadiazolines [6 a, b] and thiones [6 b, d] are 10³ -10⁴ times more reactive than corresponding ones [6 a, c]. Existence of linear relationship between log k₂ and the wave number of acetyl groups (v_c=_o) of [6 a-d] was confirmed. Further, 4-leucyl derivatives [11 a, b], obtained from [5 a, b] and Z-LeuOH, were allowed to react with HGlyOEt to give non-racemized Z-Leu-GlyOEt almost quantitatively. The polymers [14], [20] containing [ 6 ] structure were found to be useful polymeric reagents for acylation.