Short, enantiogenic syntheses of (-)-indolizidine 167B and (+)-monomorine

The enantiogenic syntheses of (-)-indolizidine 167B (1) and (+)-monomorine (2) are described. D-Norvaline and L-alanine are converted into their 1-pyrrole derivatives by reaction with 2,5-dimethoxytetrahydrofuran. Thereafter, Arndt-Eistert homologation of the N-alkanoic acid substituent, followed by rhodium(II) acetate catalyzed decomposition of its α-diazo ketone derivative, provides the relevant bicyclic precursors, the vested chirality of which directs catalytic hydrogenation affording 1 and 2. Provision for the 5-butyl side chain in 2 is made by prior Lewis acid catalyzed rearrangement of the mixed anhydride obtained from butyryl chloride and the pyrrole analogue of L-alanine.