Erythromycin series. Part 11. Ring expansion of erythromycin A oxime by the Beckmann rearrangement

The synthesis of 10-dihydro-10-deoxo-11-azaerythromycin A (11) by the Beckmann rearrangement of erythromycin A oxime (2) and reduction of the imino ether so obtained (5) is described. The structure elucidation of the new ring-expanded semisynthetic erythromycins (5) and (11) has been established on the basis of their analytical and spectral data and acid-catalysed degradation into the aglycones (7) and (13), respectively. Finally, the complete structure of ring-expanded erythronolides (7) and (13) has been determined by X-ray crystallography.