Pathways to Functionalized Heterocycles: Propargyl Rearrangement using B(C6F5)3
摘要:
The reactions of propargyl amides, ureas, carbamates, and carbonates with B(C6F5)(3) proceed via an intramolecular 5-exo-dig cyclization across the alkyne unit to yield the corresponding vinyl borate species. The generated se carbocation is stabilized by the flanking heteroatoms, allowing for isolation of oxazoline intermediates. The fate of these intermediates is strongly dependent upon the propargyl-functionalized starting material, with the carbamates and carbonates undergoing a ring-opening mechanism (propargyl rearrangement) to give cyclic allylboron compounds, while prolonged heating of the urea derivatives shows evidence of oxazole formation. In a deviation away from the reactivity of carbamates stated previously, the undergoes dealkylation at the benzylic position, liberating 5-methyloxazol-2-(3H)-one. Me benzyl carbamate substrate
研究了几种炔丙酰胺底物与氮原子上的额外取代基的反应。在水性条件下,可以选择性地获得酰氧基取代的烯丙基铵盐。通过 1 H NMR 光谱监测反应表明存在中间体。然后切换到无水反应条件允许分离和表征这些中间体,恶唑啉鎓物种。在碱性条件下处理烯丙基铵盐导致酰基从氧原子转移到氮原子,这证明这些产物不是仅通过金催化的三键直接水合形成的,同时很好地解释了两个三键中只有一个的选择性一水合。