Synthesis and stereochemistry of 3-acetyl-5-aminospiro[1,3,4-thiadiazoline-2,4 '-thioflavans]

摘要

Under acetylating conditions racemic thioflavanone thiosemicarbazones cyclize into racemic 3-acetylspiro[1,3,4-thiadiazoline-2,4'-thioflavans] and a racemic 3-acetylspiro[1,3,4-oxadiazoline-2,4'-thioflavan] with trans O(1) or S(1) and Ph(2'(eq)). Hindered rotation of the endocyclic N(3) acetyl group spirothiadiazolines caused the formation of isomers separable by HPLC. X-ray diffraction analyses, H-1-, C-13-, and N-15 NMR measurements as well as MOPAC QM calculations were performed to reveal the structures of these isomers.