Enantioselective route to ferrugine and its methyl analogue via aldol deoxygenation

A simple enantioselective approach to ferrugine (2α-benzoyltropane) and its methyl analogue (2-acetyltropane) is reported. The four-step sequence uses an enantioselective aldol reaction of tropinone with benzaldehyde or acetaldehyde, combined with an aldol deoxygenation via tosylhydrazone reduction and oxidation of the side-chain hydroxy group. The final products, ferrugine and its methyl analogue, are prepared in 35% and 23% overall yields, respectively. Both enantiomers of the products (ee 90–99%) are accessible via the same route using either enantiomer of N,N-bis(1-phenylethyl)amine hydrochloride as the chiral reagent.