A convenient allylsilane- N-acyliminium route toward indolizidine and quinolizidine alkaloids

• Roland Remuson

Beilstein J. Org. Chem. 2007, 3, No. 32, doi:10.1186/1860-5397-3-32

• chloride and CeCl3. The mixture was then hydrolysed with 1N HCl to give methylenindolizidinones 5a and 5b in a 4:1 ratio. Reduction of the mixture of lactams 5a and 5b with lithium aluminium hydride gave methylenindolizidines 6a and 6b which were separated by flash chromatography. Osmium tetroxide

• 26b with lithium aluminium hydride afforded a 4:1 mixture of methylenindolizidines 27a and 27b in quantitative yield. These isomers were separated. Palladium-catalysed hydrogenation of 27a was found to be stereoselective, giving a mixture of 28a and (-)-(dendroprimine) 22 in a 3:1 ratio. Using similar

• :20). Flash column chromatography gave pure 31a in 18% yield, but 29a and 30a could not be separated (50% yield). A mixture of the three isomers was used without purification for the next step. This mixture was then reduced with lithium aluminium hydride to give the indolizidines 28a, 22 and 29b. In