An approach to mono- and divalent <i>C</i>-aminoglycosides starting from a new enantiopure 1,2-oxazine derivative is described. The introduction of a vinyl group into the 1,3-dioxolanyl substituent of a 1,2-oxazine allowed the Lewis acid promoted preparation of a vinyl-substituted bicyclic 1,2-oxazinone. After reduction of the carbonyl group, exhaustive hydrogenolysis provided branched <i>C</i>-aminoglycosides either with β-<sc>d</sc>-talose or β-<sc>d</sc>-idose configuration. The vinyl group of the protected rearrangement product <b>8</b> also allowed a self-metathesis with Grubbs II catalyst providing a ‘dimeric’ compound as an <i>E</i>/<i>Z</i> mixture. Its hydrogenolysis furnished the divalent <i>C</i>-aminoglycoside in good overall yield.