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.

通过微波催化的级联反应，实现了对吲哚啉核的合成，其中包含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。所得到的双环亚胺离子通过Red-Al的立体选择性还原，得到了目标化合物。DFT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具有可逆性。