Direct alkenylation of indoles with alpha-oxo ketene dithioacetals: efficient synthesis of indole alkaloids meridianin derivatives.

Let's make 'meri': Metal-free direct alkenylation of indoles was realized by acid-mediated substitution reactions of alpha-oxo ketene dithioacetals with indoles in trifluoroacetic acid/dichloromethane, selectively affording beta-indolyl mono- and disubstituted alpha,beta-unsaturated carbonyl compounds (see scheme). Condensation of the indolyl/ketene monothioacetals and guanidine nitrate efficiently produced meridianin derivatives.