Synthesis of Yohimbines, 5. Enantioselective Total Synthesis of Yohimbine and β‐Yohimbine Antipodes

Abstract

Both, natural and non-natural antipodes of yohimbine (1) and P-yohimbine (2) have been synthesized from the tetracyclic keto ester 12 using second order asymmetric transformation in its resolution step. Synthese von Yohimbin-Derivaten, 54). -Enantioselektive Totalsynthese von Yohimbinund P-Yohimbin-AntipodenDie beiden naturlichen und die nicht in der Natur vorkommenden Antipoden von Yohimbin (1) und P-Yohimbin (2) wurden aus dem tetracyclischen Ketoester 12 durch wahrend der Racematspaltung stattfindende asymmetrische Umwandlung zweiter Ordnung synthetisiert.Previously we reported on the total synthesis of yohimbine alkaloids, e. g. yohimbine1.2) (l), P-yohimbine',2) (2), cc-y~himbine~,~) (3), alloyohimbine2,3) (4), 17-epi-all~yohimbine~~~' (5), and 3-epi-a-yohimbine4) (6), furthermore on their nonnatural stereoisomers, e.g. 17-epi-corynanthine2) (7), 17-epi-a-y0himbine~>~) (8), 3-epi-all0yohimbine~~~) (9), 3,l 7-epi-alloyohimbine2) (lo), and 3,l 7-epi-cc-yohimbine4) (ll), all of them in racemic formh'. P

Crystallization-Induced Diastereomer Transformations

“…), most likely via acid-catalyzed formation of retro-Mannich-type intermediate 26 as the authors suggest. Similar examples were reported much later by other groups. ,

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Enantioselective Formal Aza-Diels–Alder Reactions of Enones with Cyclic Imines Catalyzed by Primary Aminothioureas

“…1,2 Among laboratory approaches to access structurally and stereochemically complex members of this class of heterocycles, formal aza-Diels-Alder (FADA) reactions between enones and cyclic imines (Scheme 1) are particularly attractive from the perspective of convergency, resulting in the concomitant formation of a C–C and C–N bond and up to four new stereo-centers. 3,4 A proline-based protocol for enantioselective FADA reactions involving dihydro-β-carbolines has been described by Itoh and coworkers, 5 but the scope of this method has proven to be very limited.…”

Total synthesis of the monoterpenoidalkaloid (±)-tangutorine

“…1) belong to this class and form one of the principal alkaloid groups in nature that are biosynthetically derived from tryptophan. 2 This class contains some of the most important alkaloids used in medicine such as reserpine (3). 3 In 1999, a novel racemic b-carboline named tangutorine (1) was isolated by Duan and colleagues from the leaves of the Chinese medical plant Nitraria tangutorine.…”