Synthesis of Sterically Protected Xanthene Dyes with Bulky Groups at C-3′ and C-7′

Substitution of the xanthene scaffold with bulky groups at C-3′ and C-7′ is expected to protect the electrophilic central methine carbon against nucleophilic attack and inhibit stacking. However, such structures are not readily prepared via traditional xanthene syntheses. We have devised an alternative and convenient synthesis to enable facile preparation of this subset of xanthene dyes under mild conditions and in good yields.