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

• Published in: European journal of inorganic chemistry Vol. 2017; no. 34; pp. 4028 - 4048
• Main Authors: Korb, Marcus, Mahrholdt, Julia, Lang, Heinrich
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 15.09.2017
• Subjects: Alcohols; Alpha iron; Cations; Chemical synthesis; Couplings; Cross‐coupling; Ethers; Ferrocenes; Imines; Inorganic chemistry; Iron; Nitriles; Phosphates; Phosphorus; Substitution reactions; Sulfur
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201700645

The reaction of FcCH2OH with chlorophosphates gave ferrocenyl phosphates FcCH2OP(O)(OR)2 [Fc = Fe(η5‐C5H5)(η4‐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≡N functionality. A planar‐chiral ortho‐P(S)Ph2‐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)Ph2,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). Acidic treatment of planar‐chiral ferrocenylmethanols resulted in the formation of α‐ferrocenyl carbocations, which underwent electrophilic aromatic substitution reactions with electron‐rich aromatics or could be sulfurized by the thiophosphinyl group by an intermolecular process, resulting in thio ethers.