Asymmetric synthesis of planar chiral 2-mono- and 2,2′-disubstituted 1,1′-bisbenzoylferrocenes

N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

“…155 The asymmetric formation of the carbon-heteroatom (Si, P, S) bonds was also possible via ortho-lithiation in the enantioselective synthesis of planarly chiral 1,1′-bisbenzoylferrocene and diferrocenyl ketone derivatives (Schemes 10 and 11). [125][126][127] …”

Asymmetric Synthesis of PlanarChiral 2-Monosubstituted Diferrocenyl Ketones

“…Ozonolysis in dichloromethane at -78°C led to the corresponding ketone 4b in 21% yield, but decomposition was observed. Although ozonolysis turned out to be a very efficient method to cleave various ferrocenyl-SAMP-hydrazones, [6][7][8][9][10][11][12][13] in the present case this method is not practicable. So far the cleavage of the phosphinylated diferrocenyl ketones was not successful, because all attempts led to decomposition.…”

“…All new compounds gave satisfactory analytical data ( 1 H NMR, 13 General Procedure for the Preparation of the ortho-Substituted Hydrazones 3 (GP1) A Schlenk flask was filled under argon with a solution of hydrazone 2 in dry THF (20-40 mL/mmol) and cooled to -78 °C. After the addition of 2.0 equiv n-BuLi (1.6 M in hexane) the reaction mixture was stirred for 9 h at -78 °C before the electrophile (3.0 equiv) was added dropwise.…”

“…6 This method has already been proven to be of great value in the asymmetric synthesis of various ferrocenyl ligands. [7][8][9][10][11][12][13] Key step of the protocol is the highly diastereoselective ortho-metalation of diferrocenyl ketone-SAMP-hydrazone 2, which is prepared from diferrocenyl ketone 1, easily accessible by several reactions. [14][15][16] For the conversion of 1 to the corresponding SAMP-hydrazone 2 the previously described method for the synthesis of diferrocenyl ketone-N,N-dimethylhydrazone 17 was used (Scheme 1).…”

“…The use of BH 3 turned out to be advantageous, as the borane adducts are very stable. The diastereoselectivities of the planar chiral hydrazones 3 were determined by 1 H and 13 C NMR spectroscopy.…”