Asymmetric formal total synthesis of the stemofoline alkaloids: the evolution, development, and application of a catalytic dipolar cycloaddition cascade

作者：Shanahan Charles S; Fang Chao; Paull Daniel H; Martin Stephen F^*

来源：Tetrahedron, 2013, 69(36): 7592-7607.

DOI：10.1016/j.tet.2013.03.104

• Total synthesis
• Dipolar cycloaddition
• Azomethine ylide
• Stemofoline alkaloids
• Cascade reaction

A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-D-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama-Ito cyclization, and a useful modification of the Barton decarboxylation protocol.

• 出版日期2013-9-9