Enantioselective Synthesis of Amaryllidaceae Alkaloids (+)‐Vittatine, (+)‐epi‐Vittatine, and (+)‐Buphanisine

Abstract

Cat. on a hot tin roof: Enantioselective catalytic Michael addition of α-cyanoketones to acrylates under bifunctional organocatalysis was used to construct the unique arylic all-carbon quaternary stereocenter, which is synthetically crucial in the chemical synthesis of optically pure cis-aryl hydroindole alkaloids. The protocol offers an asymmetric route to (+)-vittatine, (+)-epi-vittatine, and (+)-buphanisine.

Bioinspired enantioselective synthesis of crinine-type alkaloids via iridium-catalyzed asymmetric hydrogenation of enones

“…Among these crinine-type alkaloids, seven have been previously synthesized with 8–20 steps in 0.6–13.2% yields (see also ESI † ). 7 , 8 Eleven were synthesized for the first time: (+)- and (–)-8- O -demethylmaritidine, (+)- and (–)-siculine, (–)-maritidine, (–)-epimaritidine, (+)-powelline, (+)-epipowelline, (–)-buphanidrine, (–)-flexinine and (–)-augustine. The concise, practical strategy reported here for the synthesis of crinine-type alkaloids and analogues is expected to be applicable for the rapid syntheses of other types of Amaryllidaceae alkaloids or even other types of natural products.…”

Synthetic routes to crinine and vittatine

“…[ 9 ] The syntheses in the second subgroup were empowered by sequential constructions of C and D rings. These works highlighted the implementation of a diverse range of synthetic methodologies to forge the C10b carbon, including Claisen‐type rearrangements (Muxfeldt, 1966 and Chida, 2004), [ 6,10 ] an N ‐acylaziridine rearrangement (Whitlock, 1967), [ 11 ] an enamine alkylation reaction (Martin, 1987), [ 12 ] a Diels–Alder Reaction (Cho, 2008), [ 13 ] a semi‐pinacol rearrangement (Tu, 2009), [ 14 ] an asymmetric organocatalytic Michael reaction (Fan, 2013), [ 15 ] and a Pd‐catalyzed enantioselective decarboxylative allylation (Bisai, 2018). [ 16 ]…”

“…In 2013, Fan and coworkers applied an enantioselective organocatalytic Michael reaction of α‐cyanoketone 11 and an acrylate 12 so as to forge the aryl quaternary carbon center (Scheme 13). [ 15 ] The ketoester (−)‐ 68 was treated with base to provide an annulation product 69 , which is then transformed into a cyclic vinylogous ester 70 . A reductive Stork–Danheiser transposition followed by a series of functional group manipulation afforded compound (+)‐ 63 .…”

Organocatalysis: Key Trends in Green Synthetic Chemistry, Challenges, Scope towards Heterogenization, and Importance from Research and Industrial Point of View

“…Hong and Wang reviewed advances in asymmetric organocatalytic construction of 3,3 -spirocyclic oxindoles [294]. And the applications of organocatalysts in total synthesis and natural product synthesis include enantioselective synthesis of Amaryllidaceaealkaloids (+)-vittatine, (+)-epi-vittatine, and (+)-buphanisine [295,296]. Impregnation is the immobilisation of catalytic element via electrostatic interactions with a solid support.…”