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.