Synthesis of the 6,6,5,7-tetracyclic core of daphnilongeranin B

Abstract

An efficient approach toward the synthesis of the 6,6,5,7-tetracyclic core of the daphnilongeranin B, a Daphniphyllum alkaloid, is reported. The bridged 6,6-bicyclic system was constructed using a gold(i) catalysed Conia-ene reaction, while the 5- and 7-membered rings were assembled by two diastereoselective Michael addition reactions, respectively.

Enantioselective Total Syntheses of Methanoquinolizidine-Containing Akuammiline Alkaloids and Related Studies

“…Ketolactone 9 would ultimately be obtained from enone 10 , which, in turn, would arise from a gold-catalyzed cyclization of silyl enol ether 11 . 22 Finally, 11 would be accessed in enantioenriched fashion from sulfonamide 12 and dibenzoate 13 via a Pd-catalyzed desymmetrization and subsequent manipulations. 23 …”

“…This set the stage for a pivotal gold-mediated cyclization, inspired by precedent from Li and co-workers. 22 Using our optimized protocol, silyl enol ether 11 was treated with (PMe 3 )AuCl and AgOTf, followed by quenching with tosic acid hydrate in the same pot, to ultimately afford bicycle 10 as the major product. This sequence is thought to proceed by initial formation of oxocarbenium ion intermediate 17 , which undergoes nucleophilic attack by t -BuOH to give silyl enol ether 18 .…”

Schinortriterpenoide: eine Fallstudie in Synthesedesign

“…[33] Die Synthese begann mit Ishiharas asymmetrischer intermolekularer Diels-Alder-Reaktion [51] Die Endphase der Totalsynthese ist in Schema 18 dargestellt. Durch die selektive Reduktion des Dilactons 128 mit LiAlH(Ot-Bu) 3 wurde ein Lactol erzeugt, [53] welches nach der Behandlung mit DAST das Fluorid 129 ergab. [52] Danach wurde der Alkohol 124 in einer Johnson-Claisen-Umlagerungzum Ester 125 mit 7.5:1 d.r.…”

Enantioselective Total Syntheses of Akuammiline Alkaloids (+)-Strictamine, (−)-2(S)-Cathafoline, and (−)-Aspidophylline A

“…To attempt the key gold-mediated cyclization, ketone 18 was advanced to silyl enol ether 14 , which in turn was subjected to a modification of Li’s cyclization conditions. 19 This transformation smoothly delivered a 10:1 mixture of isomeric bicyclic adducts 13 (96% ee) and 19 , even when performed on multigram scale. Although the bicycles were inseparable, exposure of the mixture to a previously established two step epoxidation/Wittig olefination sequence 5 allowed enantioenriched enal 20 to be isolated in 49% yield from silyl enol ether 14 .…”