TRANSANNULAR SULFUR-NITROGEN INTERACTIONS IN STEREOISOMERIC 1,5-THIAZOCINE DERIVATIVES - AN AB-INITIO MO STUDY

The stereoisomers of acetyl-benzo[b]naphtho[1,8-f,g]thiazocin-8(7H)-on e 13-oxide (1) were studied by ab initio MO method at the HF/3-21G lev el of theory, and the results were compared with those obtained at the semiempirical MO (AM1) level of theory. Of the eight energy-minimum s tructures optimized by the semiempirical methods two were rather disto rted in their molecular geometries. These two structures were annihila ted at the ab initio level of theory. The relative order of stability obtained by the two methods was qualitatively the same. Quantitatively , however, the corresponding structures differed somewhat from each ot her both in their geometry data and relative energy values. Bader-type electron density analysis suggested that the transannular S...N inter actions in some stereoisomers of 1,5-thiazocine derivative 1 may be re garded in the vicinity of 10% of a single bond. (C) 1997 Elsevier Scie nce B.V.