Asymmetric isochalcogenourea-catalysed (4 + 2)-cycloadditions of <i>ortho</i>-quinone methides and allenoates

Chiral isochalcogenoureas (<i>i.e.</i> isothioureas and isoselenoureas) catalyse the asymmetric (4 + 2)-cycloaddition of various allenoates with <i>ortho</i>-quinone methides. This approach provides straightforward access to different chromane derivatives with high enantioselectivities, good yields, and control of the configuration of the exocyclic double bond. Furthermore, some of the novel <i>ortho</i>-quinone methides used herein were successfully integrated into the Mayr reactivity scale by determining their electrophilicity parameter.