Synthesis and conformational analysis of phenyl-substituted 1,3,2-oxazaphosphino[4,3-a]- and 1,2,3-oxathiazino[4,3-a]isoquinolines

Through the ring closures of tetrahydroisoquinoline 1,3-amino alcohols bearing a phenyl group in the side-chain, diastereomers of novel 1- or 2-phenyl-substituted 1,3,2-oxazaphosphino[4,3-a]isoquinoline 4-oxides, and 1,2,3-oxathiazino[4,3-a]isoquinoline 4-oxides and 4,4-dioxides were prepared. NMR analysis and DFT calculations on the prepared tetrahydroisoquinoline-condensed 1,2,3-heterocycles revealed that their conformational equilibria of cis1–trans–cis2 type are influenced by the relative configuration of P-4 in the 1,3,2-oxazaphosphinanes, and by the position of the phenyl group in the 1,2,3-oxathiazines.