An easy ABD→ABCD strategy to indolo[2,3-a]quinolizin-4-one. Synthesis of deplancheine and yohimbane
The efficient synthesis of indolo[2,3-a]quinolizin-4-ones 2 is described in two steps via formal [3+3] cycloaddition reaction of α-sulfonyl tryptaminylacetamide 4 with various α,β-unsaturated esters 5 and the regioselective reduction of the resulting glut