| Abstract: | The Preininger-alkaloid, dehydro-normacrostomine ( 2b , Scheme 1) was synthesized starting from rac. α-acetyl-3,4-dimethoxybenzylcyanide (3) (Scheme 2). The key intermediate 4-acetyl-6,7-dimethoxy-1-(3,4-methylene-dioxybenzyl)isoquinoline (11) is converted via a Mannich base to the nitrile 17 (Scheme 7) which in turn is cyclized to the Preininger-alkaloid (2b) by careful hydrogenation. - Reduction of 2b with a modified Iwakuma-reagent, followed by N-formylation and subsequent LiAlH4-reduction produced (R)-(+)-macrostomine (enantiomer of 1 ) in 72% optical purity. |
