The asymmetric syntheses of pyrrolizidines, indolizidines and quinolizidines via two sequential tandem ring-closure/N-debenzylation processes.

Journal article

Concise asymmetric syntheses of (-)-lupinine, (+)-isoretronecanol, (+)-5-epi-tashiromine and (R,R)-1-(hydroxymethyl)octahydroindolizine (the azabicyclic core within stellettamides A-C) have been achieved in 8 steps or fewer from commercially available starting materials. The key steps in these syntheses involved the preparation of enantiopure β-amino esters, upon conjugate addition of lithium (R)-N-(p-methoxybenzyl)-N-(α-methyl-p-methoxybenzyl)amide to either ζ-chloro or ζ-hydroxy substituted tert-butyl (E)-hept-2-enoate, or ε-chloro or ε-hydroxy substituted tert-butyl (E)-hex-2-enoate. Activation of the ω-substituent as a leaving group led to SN2-type ring-closure, which occurred with concomitant N-debenzylation via an E1-type deprotection step, to give the corresponding pyrrolidine or piperidine in good yield. Subsequent alkylation of these enantiopure azacycles, followed by a second ring-closure/concomitant N-debenzylation step formed the pyrrolizidine, indolizidine or quinolizidine motif, and reduction with LiAlH4 gave the target compounds in diastereoisomerically and enantiomerically pure form.

Authors: Davies, S; Fletcher, A; Foster, E; Houlsby, I; Roberts, P

• Publication status: Published
• Publisher: Royal Society of Chemistry
• Journal: Organic and biomolecular chemistry
• Volume: 12
• Issue: 45
• Pages: 9223-9235
• Publication date: 2014-12-01
• DOI: 10.1039/c4ob01737d
• EISSN: 1477-0539
• ISSN: 1477-0520
• Language: English