Improved Access to Chiral Tetranaphthoazepinium-Based Organocatalysts Using Aqueous Ammonia as Nitrogen Source.

The class of 3,3'-diaryl substituted tetranaphthobisazepinium bromides has found wide application as highly efficient -symmetrical phase-transfer catalysts (PTCs, Maruoka type catalysts). Unfortunately, the synthesis requires a large number of steps and hampers the build-up of catalyst libraries which are often desired for screening experiments. Here, we present a more economic strategy using dinaphthoazepine as the common key intermediate. Only at this stage various aryl substituents are introduced, and only two individual steps are required to access target structures. This protocol was applied to synthesize ten tetranaphthobisazepinium compounds -. Their efficiency as PTCs was tested in the asymmetric substitution of -butyl 2-((diphenylmethylene)amino)acetate. Enantioselectivities up to 92% have been observed with new catalysts.