Unexpected copper mediated benzyl O→O migration during an Ullmann ether coupling

The synthesis of a highly functionalized phenolic diaryl ether 5,5′-oxybis(4-hydroxy-3-methoxybenzaldehyde) (1) potentially interesting as a new scaffold for drug design, has been carried out using Ullmann coupling conditions. An unusual benzyl migration in o-benzyloxyphenol moiety occurred during this reaction leading to an unexpected compound identified as 4-(benzyloxy)-3-(2-(benzyloxy)-4-formyl-6-methoxyphenoxy)-5-methoxy benzaldehyde (7). A rationale for this migration process is proposed.