Synthesis of the Indolizidine Core of Virosinine A via a Microwave-Promoted Cascade Cyclization Involving Iminyl Radicals

The indolizidine core of virosinine
A was synthesized
by means
of a microwave-promoted cascade reaction featuring 5-exo-trig iminyl radical cyclization, thiyl radical
elimination, and intramolecular imine alkylation. The resulting bicyclic
iminium ion underwent stereoselective reduction by Red-Al to deliver
the target compound. DFT calculations suggested that both the radical
cyclization and thiyl radical elimination steps are reversible at
high reaction temperatures.

通过微波促进的级联反应合成了一种名为 virosinine A 的吲哚啉核心化合物，该反应包括5-外-三键亚胺自由基环化、硫自由基消除和分子内亚胺烷基化。生成的双环亚胺阳离子通过Red-Al进行立体选择性还原，从而得到目标化合物。密度泛函理论计算表明，在高温反应条件下，自由基环化和硫自由基消除步骤均为可逆过程。