Rhodium-catalyzed diastereoselective synthesis of highly substituted morpholines from nitrogen-tethered allenols

Rhodium-catalyzed intramolecular cyclization of nitrogen-tethered allenols was investigated for the synthesis of functionalized morpholines. By using this strategy, various N-protected 2,5- and 2,6-disubstituted as well as 2,3,5- and 2,5,6-trisubstituted morpholines were obtained via an atom-economic pathway with high to excellent yields, diastereo- and enantioselectivities (up to 99% yield, up to >99 : 1 dr and up to >99.9 ee). The utilities of the synthesized morpholines in ozonolysis, hydration, metathesis and epoxidation reactions were also investigated.