Carbohydrate Auxiliaries in Stereoselective Syntheses of Decahydroquinoline Alkaloids

A tribute to Professor Horst Kunz

“…When the N-galactosyl substituent was exchanged for a (flat) phenoxycarbonyl group, the cis-fused pumiliotoxin framework was formed, but in the presence of the Ngalactosyl group, protonation of the enolate was directed under contra thermodynamic control to result in the trans-fused (4-epi, histrionicotoxin series) structure. 48 Control of the CH-acidity of an intermediary piperidinone through the N-galactosyl group is also responsible for the preferred formation of the all-cis nupharamine 46, which can be converted to the trans-substituted epimer 46-e by treatment with base. 49 The scope of this stereoselective methodology becomes obvious if one keeps in mind that the series of opposite The product has the opposite configuration of the heterocycle compared to 42 although D-galactosyl served as the differentiating substituent in both processes.…”

Quinoline, quinazoline and acridone alkaloids

“…The use of tetra-O-pivaloyl-β--galactopyranosylamine 119 as a chiral auxiliary in enantioselective and stereochemically complementary syntheses of several stereoisomers of pumiliotoxin C has been investigated by Kunz and co-workers. 71 Imines 120 formed from this precursor underwent highly diastereoselective annulation with the diene 121 in the presence of zinc() chloride to give the dihydropyridones 122 and 123 in 68% yield (Scheme 4). Diastereoselective conjugate addition of appropriate cuprates then yielded the 2,6-cis-disubstituted piperidinones 124 and 125 which, with suitable manipulation of the functionalised side chains, afforded octahydroquinolinones 126 and 127 possessing opposite absolute configurations at the C-2 and C-8a sites.…”

InCl3-catalyzed asymmetric aza-Friedel–Crafts reaction of indoles with imines generated from O-pivaloylated β-d-galactosylamine

“…16 Chiral homoallyl amines, [17][18][19] a-aminophosphonic acid derivatives, 15,20 and a-amino (phenyl)methyl(phenyl)phosphinic acids 21 were also synthesized with this chiral amine. In recent years, some examples of alkaloid synthesis [22][23][24][25] were reported using Domino MannichMichael reactions, [26][27][28][29][30] in which O-pivaloylated b-D-galactosylamine was utilized to generate the crucial chiral center. The use of O-pivaloylated b-galactosylamine as a chiral auxiliary to induce high enantioselectivity has been well defined.…”