Enantioselective Synthesis of Ferrocene‐ or Cymantrene‐Fused Planar‐Chiral Phospholes

Planar‐chiral ferrocene‐fused phosphole ( S )‐ 1a was prepared in an enantiomerically pure form by enantioselective transformation. The synthesis was started with Kagan's chiral ferrocenyl acetal (–)‐ 2a , and bromo and ( Z )‐2‐bromovinyl substituents were introduced at the 1‐ and 2‐positions of the ferrocene platform in ( S )‐ 6a with controlling its planar chirality. The double Li/Br exchange on ( S )‐ 6a followed by the reaction with PhPBr 2 provided ( S )‐ 1a in excellent yield. The structure of ( S )‐ 1a was determined by X‐ray crystallography. Planar‐chiral cymantrene‐fused phosphole ( S )‐ 1b was also prepared by an analogous asymmetric transformation starting with Jaouen's chiral cymantrenyl acetal (+)‐ 2b .