Synthesis of (-)-N-Acetylslaframine by C-1, C-5 Bis-hydroxyalkylation of (S)-2-(N,N-Dibenzylamino)-1,5-pentanediol via Highly Diastereoselective Lithiation of the Dicarbamate

Abstract

(-)-N-Acetylslaframine, a stable form of the indolizidine alkaloid (-)-slaframine, has been synthesised by a new strategy. Applying highly stereoselective lithiation and substitution reactions, C-2, C-3 and C-8 of the bicyclic skeleton were introduced to an l-glutamic acid derived diol dicarbamate.

Key words

indolizidines - chiral 2-amino-1-ω-alkanediols - lithiated dicarbamates - diastereoselectivity - (-)-sparteine

References

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2

X-ray analysis.

10

Since polymerisation of ethylene oxide competes with substitution, the yields vary strongly when changing the reaction conditions.

11

Even lithiation in one methyl group of a O-dimethylphenyl­-silyl residue was observed.

14

Using CDCl₃, fresh de-acidification by filtration over basic Al₂O₃ was necessary. Otherwise, signal broadening or the signal set of a second compound (presumably the slowly exchanging ammonium salt of 2) appears.

15

Eight different values between -10.0 and -18.8 have been reported for [α]_D of 2. [4]