Planar Chirality from the Chiral Pool: Diastereoselective Anionic Phospho-Fries Rearrangements at Ferrocene

Exclusively, the anionic phospho-Fries
rearrangement has successfully
been adopted on chiral ferrocenyl phosphates, resulting in diastereomeric
enriched 1,2-P,O-phosphonates (up to 95% de), which
can further be converted to an enantiomerically pure phosphane. A
simple synthetic protocol for the preparation of all starting materials
based on several chiral-pool alcohols, chiral (di)­chlorophosphates,
and the respective ferrocenyl phosphates is reported. Optimized reaction
conditions for the anionic phospho-Fries rearrangement allow conversions
at ambient temperature and the use of variable lithium amid bases
and diamines in hexane, ensure virtually quantitative yields, and
avoid side reactions. The (bi)­cyclic alkyl substituents result in
air- and moisture-stable compounds and furthermore allow the conversion
of 1,1′-substituted derivatives to 1,1′,2,2′-functionalized
ferrocenes, which is reported for the first time. Simultaneous rearrangements
at diferrocenyl phosphates to phosphinates and even 2-hydroxy-1,3-bis­(phosphonato)
ferrocenes and their workup under ambient conditions can be performed.
Single-crystal diffraction analysis allowed the determination of the
absolute configuration of the planar chirality of two diastereomerically
pure ferrocenes being the Rp isomers.
Furthermore, strong T-shaped π–π interaction patterns
between aromatic C5H3 and C5H4 cycles for three compounds are observed.