Synthetic and spectroscopic study of 5‐amino‐2‐acyl‐1,2,4‐thiadiazolin‐3‐ones

Abstract

Abstract5‐Amino‐2‐acyl‐1,2,4‐thiadiazolin‐3‐ones 2–1 can be synthesized from 5‐amino‐2H‐1,2,4‐thiadiazolin‐3‐one (1–1) via a selective acylation with an acid anhydride in pyridine. The 1H nmr spectral characteristics of 5‐amino‐2‐acyl‐1,2,4‐thiadiazolin‐3‐ones 2–1 is in particular, compared with 5‐amino‐2H‐1,2,4‐thiadiazolin‐3‐one (1–1) and 5‐amino‐2‐alkyl‐1,2,4‐thiadiazolin‐3‐ones 1–2, 1–3. The 5‐amino group of 2–1 appeared as two peaks in its 1H nmr spectrum, which merged to a single peak at a higher temperature, while those of compound 1–1, 1–2 and 1–3 appear only as a single peak. The restricted rotation of the C(5)‐N(5) (at amino) bond of 5‐amino‐2‐acetyl‐1,2,4‐thiadiazolin‐3‐one (2a‐1) is about 14.5 Kcal/mol.