STEREOCHEMICAL STUDIES .134. SATURATED HETEROCYCLES .138. SYNTHESIS AND STEREOCHEMISTRY OF STEREOISOMERIC 1,3-OXAZINO[4,3-ALPHA]ISOQUINOLINE AND 1,3-THIAZINO[4,3-ALPHA]ISOQUINOLINE

Starting from the 6,7‐dialkoxy‐1‐[bis(hydroxymethyl)methyl]‐1,2,3,4‐tetrahydroisoquinolines 2 and 3, the 4‐imino‐substituted 1‐(hydroxymethyl)‐9,10‐dialkoxy‐2H, 4H‐1,6,11b‐tetrahydro‐1.3‐oxazino‐and ‐thiazino [4,3‐a]isoquinoline diastereomers 6a‐c, 7a‐c, 8a‐c, 9a‐c, 14, and 15 and the 4‐substituted 1,6,7,11b‐tetrahydro 1,3‐oxazino[4,3‐a]isoquinoline diastereomers 16–24 were prepared. the relative configurations and the predominant conformation of these products were determined by NMR spectroscopy and for 18 by X‐ray diffraction methods. the prepared 1,3‐oxazino[4,3‐a]isoquinoline diastereomers have predominantly trans conformations (16, 18, 22, 23), whereas cis conformations (cis‐A) prevail for 20, 21 and f24. Thus, the first evidence for either trans‐ or cis‐A conformations in 1,3‐oxazino[4,3‐a] isoquinolines is presented. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim