Anion Mask Strategy Enabling Organolithium Species Bearing Formyl Groups: Protecting-Group-Free Synthesis for Unsymmetric Dicarbonyl Arenes

The protecting groups for carbonyl groups, in particular, a formyl group, are one of the milestones of recent organic synthesis but today are treated as a limitation in terms of step economy. Herein, we report a novel strategy for treating carbonyl groups as nucleophile-tolerant functional groups. Utilizing amino groups as poor leaving groups, "masked" carbonyl groups were designed and were monitored by in-line analyses. We achieved lithiation of aryl bromide bearing "masked" carbonyl groups, followed by reactions with electrophiles. With this strategy, we demonstrated syntheses of unsymmetric dicarbonyl arenes, which basically require protecting groups.