DDQ-promoted direct C5-alkylation of oxazoles with alkylboronic acids via palladium-catalysed C–H bond activation

A novel and concise C5-alkylation of oxazoles using alkylboronic acids as alkyl donors via Pd(II)-catalysed C–H bond activation has been achieved in moderate to good yields with satisfactory functional group tolerance. Instead of commonly used BQ as a key promoter, DDQ was discovered to be a better additive that significantly promoted this alkylation. This efficient and advanced method represents the first C(sp²)–C(sp³) cross-coupling reaction at the C5-position of oxazoles, which is particularly attractive due to its potential applications in the late-stage functionalization of oxazole-containing bioactive molecules.