Synthesis of a 3‐Arylisoquinoline Alkaloid, Decumbenine B

Abstract

The synthesis of a 3‐arylisoquinoline alkaloid, decumbenine B, was accomplished in a reaction sequence based on the formation of an indolizine ring {dibenz[a,f]indolizin‐5(7H)‐one} followed by its cleavage at the amide bond, starting with an interaction of 5,6‐(methylenedioxy)isoquinoline with 2‐bromo‐5,6‐(methylenedioxy)benzoyl chloride in the presence of Bu3SnH.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Isoquinoline synthesis by C-H activation/annulation using vinyl acetate as an acetylene equivalent

“…Encouraged by the formation of a single regioisomer in the case of the methylenedioxy-substituted 5o, we were interested to apply the methodology to the corresponding aldoxime 6 in the hope of preparing the isoquinoline intermediate 7. Compound 7 has previously been prepared as an intermediate 28 in the synthesis of decumbenine B, a naturally occurring alkaloid used for the treatment of hypertension, rheumatoid arthritis and sciatic neuraligia. 29 The five step route developed by Orito et al 28 involves a key Pictet-Gams cyclisation to afford the isoquinoline 7 in a yield of 25% over five steps.…”

“…Compound 7 has previously been prepared as an intermediate 28 in the synthesis of decumbenine B, a naturally occurring alkaloid used for the treatment of hypertension, rheumatoid arthritis and sciatic neuraligia. 29 The five step route developed by Orito et al 28 involves a key Pictet-Gams cyclisation to afford the isoquinoline 7 in a yield of 25% over five steps. However, to our knowledge, aldoxime derivatives have not yet been employed in direct isoquinoline annulation reactions, and this provided an ideal opportunity to test their suitability.…”

Synthesis of Pyrrolo[1,2-b]isoquinolines via Gold(I)-Catalyzed Cyclization/Enyne Cycloisomerization/1,2-Migration Cascade

“…Selective reduction of ester 9 delivered the allylic alcohol 10, which is a decumbenine B analogue. 13 Based on our observations and previous reports, 5 a plausible mechanism 14 The reaction was conducted at rt for 3 h. c The reaction was conducted at rt for 6 h. d The reaction was conducted at 60 °C for 3 h. e The reaction was conducted at 100 °C for 3 h.…”

Direct Metal‐Catalyzed Regioselective Functionalization of Enamides

“…An interesting strategy for the synthesis of 3-arylisoquinoline alkaloids that rely on an intramolecular Heck cyclization of endocyclic enamides was explored by Orito and co-workers (Scheme 7). [9] The authors also used this Pd-catalyzed cyclization as the key step for the formation of a ring system characteristic of isoindolobenzazepine. [10] A similar strategy was developed for the synthesis of indoles.…”