Abstract
The cyclizations of tetrahydroisoquinoline 1,2‐amino alcohols with phenylphosphonic dichloride, bis(2‐chloroethyl)phosphoramidic dichloride, thionyl chloride and sulfuryl chloride were utilized to synthesize 1,5,6,10b‐tetrahydro‐1,3,2‐oxazaphospholo[4,3‐a]isoquinolines (2, 3), 1,5,10,10a‐tetrahydro‐1,3,2‐oxazaphospholo[3,4‐b]isoquinolines (8, 9), 1,5,6,10b‐tetrahydro‐1,2,3‐oxathiazolo[4,3‐a]isoquinolines (4–6) anda 1,5,10,10a‐tetrahydro‐1,2,3‐oxathiazolo[3,4‐b]isoquinoline (11), which are the first representatives of these ring systems. NMR spectroscopic analysis revealed the existence of conformational equilibria that are fast on the NMR timescale. Theoretical DFT calculations pointed to the participation of generally two preferred conformers in the conformational equilibria; the positions of the equilibria were indicated by the experimental NMR spectroscopic parameters, and they are in good agreement with the theoretically calculated energy differences of the participating conformers. For two compounds, which could be not isolated (10, 12), both the preferred conformers and the stereochemistry could be concluded from the DFT calculation results. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)