4,5- and 2,5-additions to oxazoles

An investigation of the reaction of variously substituted oxazoles 1a-j with Br₂ in methanol revealed the formation of non-aromatic addition products. In general the presence of an aromatic substituent at the 4-position of oxazoles or the presence of a 4-methyl group if the 2-substituent is also aliphatic favors formation of 2,5-dimethoxy-3-oxazolines 3, while an aromatic substituent at the 2-position favors formation of ring-opened amides 2 or 7 or of 4, 5-dimethoxy-2-oxazolines 5. Valuable information about intermediates in these reactions can be obtained by following the bromination of 1 in CD₃OD by ¹H- and ¹³C-NMR.