Dedicated to Professor Grzegorz Mlostoń on the occasion of his 65th birthday
Abstract
A three-step approach to enantiomerically pure 3-aminoseptanoside derivatives by addition
of lithiated methoxyallene to δ-silylated aldopentose-derived nitrones, followed by
Brønsted acid mediated cyclization and chemoselective N–O bond scission is presented.
For the addition of the methoxyallene anion leading to 3,6-dihydro-1,2-oxazines, excellent
syn-diastereoselectivities were observed in the case of d-xylose- and l-arabinose-derived nitrones, whereas the d-ribose analogue provided syn- and anti-configured products in an approximately 2:1 ratio. Subsequent proton-induced reactions
provided the corresponding dimethyl ketals as kinetic products, which slowly converted
into bicyclic oxepanoides formed in a highly cis-selective manner. The final reductive ring opening was performed in good yields by
using an excess of samarium(II) iodide. With a selected compound it was demonstrated
that this type of product is a suitable precursor for the preparation of polyfunctionalized
oxepanopyrrolidine derivatives.
Key words
allenes - nitrones - heterocycles - 1,2-oxazines - oxepanes - septanosides