(Planar-Chiral) Ferrocenylmethanols: From Anionic Homo Phospho-Fries Rearrangements to -Ferrocenyl Carbenium Ions

The reaction of FcCH(2)OH with chlorophosphates gave ferrocenyl phosphates FcCH(2)OP(O)(OR)(2) [Fc = Fe(eta(5)-C5H5)(eta(4)-C5H4)], which readily separate into phosphate anions and ferrocenyl carbo-cations. The latter species undergoes consecutive reactions, for example, electrophilic aromatic substitutions. When nitriles, instead of alcohols, are treated with FcLi or tBuLi and chlorophosphates, chiral-pool based ferrocenylimino phosphoramidates Fc-CR=N-P(O)(OR*)(2) are formed, which are promising candidates for anionic homo phospho-Fries rearrangements. Moreover, the sterically demanding chiral chlorophosphate with R* enabled oxidative couplings of the imines to form a diferrocenylazine. Similarly, the reaction of Fc-Li with 9-anthrylnitrile produced a 10-ferrocenyl-substituted product, contrary to a reaction at the C equivalent to N functionality. A planar-chiral ortho-P(S)Ph-2-functionalized ferrocenylmethanol also gave carbo-cations under acidic conditions. These species can be sulfurized in a unique way giving thio ethers, whereby the in situ formed 1,2-P(S)Ph-2,CH2+ ferrocene cation acts as the sulfur and electron source. However, lowering the substrate concentration prevents sulfur migration, resulting in electrophilic substitution reactions with aromatic solvents. Planar-chiral ferrocenylmethyl thio or anisyl derivatives were applied as ligands in Pd-catalyzed Suzuki-Miyaura C,C cross-couplings for the atroposelective synthesis of hindered biaryls with up to 26% ee at low catalyst loadings (1 mol-% Pd).