Tuning the Structure of Phosphahelicenes for Targeted Applications in Enantioselective Phosphine Organocatalysis

The use of phosphahelicenes as nucleophilic organocatalysts for [3+2] cyclization reactions between allenoates and 2-benzylidenemalononitriles has been extended by the systematic screening of phosphines with different helical scaffolds and substitution patterns. Among others, a new series of phosphahelicenes have been prepared by bromination/Suzuki coupling reactions of a pre-formed phosphahelicene. This late bromination approach represents a suitable strategy for accessing a broad variety of substituted phosphahelicenes from a single intermediate. It represents a powerful tool for the catalysis-oriented optimization of their structural features.