Efficient and Practical Syntheses of Enantiomerically Pure ( S )‐(−)‐Norcryptostyline I, ( S )‐(−)‐Norcryptostyline II, ( R )‐(+)‐Salsolidine and ( S )‐(−)‐Norlaudanosine via a Resolution‐Racemization Method

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Four racemic tetrahydroisoquinolines ( RS )‐(±)‐ 1–4 were prepared from homoveratrylamine via amidation, Bischler‐Napieralski reaction and the subsequent reduction. The enantiomerically pure tetrahydroisoquinolines ( S )‐ (−)‐norcryptostyline I [( S )‐(−)‐ 1 ], ( S )‐(−)‐norcryptostyline II [( S )‐(−)‐ 2 ], ( R )‐(+)‐salsolidine [( R )‐(+)‐ 3 ] and ( S )‐(−)‐norlaudanosine [( S )‐(−)‐ 4 ] were then obtained in 45%, 40%, 41% and 38% yields, respectively, via resolution of the racemic compounds ( RS )‐(±)‐ 1–4 with half equivalent of chiral acids. In addition, the enantiomerically enriched compounds ( R )‐(+)‐ 1 , ( R )‐(+)‐ 2 , ( S )‐(−)‐ 3 and ( R )‐(+)‐ 4 from the mother liquors were efficiently racemized via a one‐pot redox method in almost quantitative yields.