Synthesis of (±)-laudanoeine and a study of 1-benzyl-3-isoquinoione intermediates

A keto acid (2) has been converted to tetrahydropapaverine and (±)-laudanosine. Some intermediate 3-isochromanone ( 3 ) and 3-isoquinolone ( 4 and 5 ) derivatives have been investigated and structures assigned to these compounds from spectroscopic studies. The 3-isoquinolone tautomer with the o-quinonoid structure predominates over the 3-isoquinolinol form, but the analogous oxygen derivative has preferentially a stilbene structure ( 3 ) with an intact benzene system.