Oxazole reaction with free radicals

Enolizable ketones were converted directly into their a-hydroxy dimethyl acetals upon reaction with DIB and methanolic potassium hydroxide at room temperature. If, during work up, there was acid treatment, then a-hydroxyketones were directly obtained. Numerous examples are known for such transformation, e.g. with 3-pentanone, acetophenones, 2,6-diacetylpyridine [16], tropan-3-one [17], -amino-ketones of great structural variety [18], etc. even a free radical reacted successfully in this way [19]. This conversion for an acetyl-oxazole served for the preparation of pyrimidine derivatives. 

Imidazolidine and imidazoline derivatives were formed when dialdose derivatives reacted with 2,3-bis(hydroxylamino)-2,3-dimethylbutane (Scheme 60) oxidation of these derivatives afforded stable free radicals that were examined by e.s.r. spectroscopy. Several oxazole and thiazolidine derivatives having C-5 and C-6 of 3-0-benzyl-l,2-0-isopropylidene-jS-L-idofuranose as part of the heterocyclic ring, and a new class of bicyclic thiazolidine derivative (172) have been prepared by the reactions shown in Scheme 61. The bis(l,3,4-oxadia-zole) derivative (173) has been prepared by condensative cyclization of 2,3,4,5-tetra-O-acetylgalactaric acid bis(benzoylhydrazide) with triethyl orthoformate in p-dioxan. Other heterocyclic derivatives are referred to in Chapters 14 and 15. 

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