Asymmetric Synthesis of Isoquinoline Alkaloids: (R)‐ and (S)‐2‐Ethoxycarbonyl‐1‐Formyl‐6, 7‐Dimethoxy‐1,2,3,4‐Tetrahydroisoquinoline as Versatile Precursors

A method is described for the preparation of (R)‐ and (S)‐2‐ethoxycarbonyl‐1‐formyl‐6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline involving a Swerntype oxidation of (R)‐ and (S)‐2‐ethoxycarbonyl‐1‐hydroxymethyl‐6, 7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline {(R)‐ and (S)‐2‐(ethoxycarbonyl)calycotomine}. The utility of these aldehydes in asymmetric synthesis of isoquinoline alkaloids has been demonstrated by their conversion into (S)‐ and (R)‐xylopinine, respectively; also, the (R)‐aldehyde has been employed for the synthesis of (8S,14S)‐coralydine.