A short synthetic route to the calystegine alkaloids

A Short Synthesis of (+)-Cyclophellitol

[reaction: see text] A new synthesis of (+)-cyclophellitol, a potent beta-glucosidase inhibitor, has been completed in nine steps from D-xylose. The key transformations involve a zinc-mediated fragmentation of benzyl-protected methyl 5-deoxy-5-iodo-xylofuranoside followed by a highly diastereoselective indium-mediated coupling with ethyl 4-bromocrotonate. Subsequent ring-closing olefin metathesis, ester reduction, olefin epoxidation, and deprotection then afford the natural product. This constitutes the shortest synthesis of (+)-cyclophellitol reported to date.

Catalytic Enantioselective Indium-Mediated Allylation of Hydrazones

[reaction: see text] A facile and highly selective indium-mediated allylation of hydrazones utilizing BINOL ligands is described. Chiral (R)-3,3'-bistrifluoromethylBINOL afforded homoallylic amines in up to 97% ee with stoichiometric ligand. Employing only 10 mol % ligand afforded selectivity of up to 92% ee.

Highly diastereoselective indium-mediated allylation of chiral hydrazones

The indium-mediated allylation of chiral hydrazones was investigated. Essentially complete diastereoselectivity and quantitative yields were obtained for substrates derived from both aromatic and aliphatic aldehydes. [reaction--see text]

A Short Route toward Chiral, Polyhydroxylated Indolizidines and Quinolizidines

In this paper, a rapid route toward functionalized bicyclic alkaloids is presented. In only three steps, an easily accessible carbohydrate derivative was converted into iodomethyl indolizidine 13, which can equilibrate to the corresponding iodoquinolizidine 15. We provide strong evidence that this equilibration proceeds via an aziridinium ion intermediate. Furthermore, nucleophilic substitution of the iodomethyl indolizidine as well as the aziridinium intermediate gives access to highly functionalized indolizidine and quinolizidine alkaloids.