CHIRAL SULFUR-COMPOUNDS .24. A CONVENIENT SYNTHESIS OF 2-METHOXY-1-NAPTHYL SULFOXIDES IN HIGH ENANTIOMERIC PURITY - A NEW ASYMMETRIC-SYNTHESIS OF 1-BENZYL-1,2,3,4-TETRAHYDROISOQUINOLINES

The synthesis of diastereomerically pure (-)-(S) menthyl 2-methoxy-1-n aphthalenesulfinate (5) is reported. The reaction of (5) with methylma gnesium iodide or benzylmagnesium chloride gives (+)-(R) benzyl 2-meth oxy-1-naphthyl sulfoxide, (7) and (8) respectively, in high enantiomer ic purity (98% ee). Lithiated (8) undergoes addition to 6,7-dimethoxy- 3,4-dihydroisoquinoline N-oxide (2) to give a 1-benzyl-1,2,3,4-tetrahy droisoquinoline derivative (9) with high product diastereoselection (d . r. 97 : 4). The stereochemistry of (9) was determined by a single cr ystal X-ray structure determination.