[288-42-6] · C3H3NO · Oxazole · (MW 69.07)
Physical Data: mp -87 to -84 °C; bp 69-70 °C; d 1.050 g cm-3; l
Form Supplied in: colorless oil.
Oxazole functions as an azadiene in the Diels-Alder reaction.2 The resulting [4 + 2] product is normally not isolated, instead rearranging to pyridines (eq 3). High regioselectivity has been reported6 for this reaction (see also 4-Phenyloxazole). Oxazole can also perform as a dienophile, as in the reaction with tetrazines (eq 4).7
Treatment of oxazole with one equivalent of Ozone cleaves the C-C bond and yields N-formylformamide (4) (eq 5).3 Subsequent addition of primary or secondary amines gives high yields of formamides (eq 6). Formylation of alcohols is substantially slower.
Metalation at C-2 of oxazole is rapid with n-Butyllithium, and the metalated product is in equilibrium with the ring-opened isocyanide (eq 7). Highly reactive electrophiles yield products from the enolate form of (5) (eqs 8 and 9), while less reactive electrophiles react with the carbanion form (eqs 10 and 11).8
Palladium-catalyzed coupling of chloropyrazines with oxazole occurs at C-2, yielding the diaryl in good yield (eq 12).9
Scott McN. Sieburth
State University of New York at Stony Brook, NY, USA