The yields were determined by 1H NMR analysis of the crude product using CH2Br2 as an internal standard. Enantiomeric ratios (er) were determined by chiral high-performance liquid chromatography. The absolute configurations of L13, L21, L35 and L40b were determined by X-ray crystallography (see supplementary material). HFIP, hexafluoro-2-propanol; Me, methyl group; Pr, propyl group; Bn, benzyl group; Ph, phenyl group.