Abstract
Starting from 5-carboxyethyl-5,6-dihydroindolizine, the title alkaloid was obtained in 25% overall yield via differently C5-substituted 5,6-dihydroindolizines and final exhaustive hydrogenation. An alternative strategy for the synthesis of optically active indolizidine 167B and analogues still based on 5,6-dihydroindolizine intermediates is given.
Keywords
- (-)-indolizidine 167B - 5,6-dihydroindolizines - synthesis - 4-(pyrrol-1-yl)butanal - enantioselective hydrogenation
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13 The evaluation of ee of the olefin (-)-6′ was accomplished by transforming it into the new partially hydrogenated 5-ethyl-5,6,7,8-tetrahydroindolizine (8 ; Scheme
[2 6′ , was separated into its enantiomers by chiral gas chromatography [CHIRALDEX G-TA (γ-cyclodextrin trifluoroacetyl, 50 m × 0.25 mm) capillary column]. The chromatographic conditions were set up for analysing a racemic sample of 8
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