Palladium-Catalyzed Direct Alkenylation of 2‑Oxazolones: An Entry to 3,4,5-Trisubstituted 2‑Oxazolones

Described herein is a novel method
for the synthesis of 3,4,5-trisubstituted
2-oxazolones featuring the first Pd-catalyzed dehydrogenative alkenylation
of 2-oxazolones, which is realized by employing 10 mol % of Pd­(OAc)2 as the catalyst and the use of readily available Cu­(OAc)2 as the oxidant. A wide range of functional groups, such as
F, Cl, Br, OMe, ester, ketone, amide, alkyl, and aryl substituents,
are found to be compatible under the reaction conditions. The utilization
of the C–H functionalization strategy provides a straightforward,
convenient, and highly atom-economical approach for the construction
of 3,4,5-trisubstituted 2-oxazolones. It is worth noting that the
4-alkenyl 2-oxazolones can be smoothly converted into naphtho­[1,2-d]­oxazol-2-ones via a photochemical transformation.

本研究报道了一种用于合成3,4,5-三取代-2-恶唑烷酮（3,4,5-trisubstituted 2-oxazolones）的新型方法，该方法首次实现了2-恶唑烷酮（2-oxazolones）的钯催化脱氢烯基化反应，以10 mol%的乙酸钯(II)（Pd(OAc)2）作为催化剂，以易得的乙酸铜(II)（Cu(OAc)2）作为氧化剂。该反应条件下可兼容多种官能团，包括氟、氯、溴、甲氧基、酯基、酮羰基、酰胺基、烷基及芳基取代基。通过采用C-H官能化（C–H functionalization）策略，可为3,4,5-三取代-2-恶唑烷酮的构建提供一条简洁、便捷且原子经济性极高的合成路径。值得注意的是，4-烯基取代的2-恶唑烷酮可通过光化学转化（photochemical transformation）顺利得到萘并[1,2-d]恶唑-2-酮。