Efficient Asymmetric Synthesis of Planar‐Chiral Bisferrocenes

Abstract

SAMP auxiliary-derived monosubstituted diferrocenyl ketones have been subjected to ortho-metalation/functionalization reactions to prepare chiral disubstituted bisferrocenes. The reactions proceeded in low to moderate yields (20-54 %) and excellent stereoselectivities (97 -Ն 99 % ee, Ն 96 % de), however low regio-selectivities were obtained in several cases. Monosubstituted bisferrocenes, containing only a planar-chiral element, were excellent substrates in the same ortho-metalation/functionalization reaction affording disub-

Synthesis and (spectro)electrochemistry of mixed-valent diferrocenyl–dihydrothiopyran derivatives

“…Sulphide 1 was prepared via the hetero-Diels-Alder cycloaddition of diferrocenylthioketone 50,51 with 2,3-dimethyl-1,3-butadiene in a sealed glass-tube at 75°C (Experimental section). 52 After appropriate work-up, compound 1 was obtained as a red solid in 65% yield.…”

“…This S-atom reactivity allows us to synthesise three closely related derivatives 1-3 and investigate the influence of the different electron-withdrawing character of the aliphatic bridge on the IVCT properties of the mixed valence species 1 + -3 + . Sulphide 1 was prepared via the hetero-Diels-Alder cycloaddition of diferrocenylthioketone 50,51 with 2,3-dimethyl-1,3-butadiene in a sealed glass-tube at 75 °C (Experimental section). 52 After appropriate work-up, compound 1 was obtained as a red solid in 65% yield.…”

Improved Syntheses of 1,2‐Disubstituted Ferrocenes

“…1,1′‐Disubstituted ferrocenes, which are usually obtained by 1,1′‐dilithiation of ferrocene with butyllithium/tetramethylethylenediamine (BuLi/TMEDA) followed by reaction with an electrophile, attract attention in the context of molecular wires, ferrocenophanes, and possible interactions between the substituents , , . 1,2‐Disubstituted ferrocene derivatives are often obtained by ortho ‐metallation reactions . The presence of chiral substituents such as enantiopure oxazoline or sulfoxide moieties facilitates diastereoselective reactions leading to planar‐chiral derivatives in enantiopure form .…”

Selective Syntheses of Planar-Chiral Ferrocenes

“…The SAMP-hydrazone method can be extended to the synthesis of planar-chiral diferrocenyl ketones, starting from ferrocene 159 (Scheme ). Hydrazone ( S )- 168 gives not unexpectedly ( S , S p )- 169 in ≥96% de, which yielsd upon hydrazone cleavage only planar-chiral monosubstituted diferrocenyl ketones ( S p )- 170 almost enantiomerically pure (97–99% ee) (Scheme ) . In contrast, the attempted introduction of a functionality E′ at the second ferrocenyl moiety, subsequent to the synthesis of hydrazone ( S , S p )- 169 , is, in addition to being highly diastereoselective (≥96% de), less regioselective, forming ferrocene 171 or 172 or mixtures thereof depending on the nature of the substituent E (Scheme ) .…”

“…Hydrazone ( S )- 168 gives not unexpectedly ( S , S p )- 169 in ≥96% de, which yielsd upon hydrazone cleavage only planar-chiral monosubstituted diferrocenyl ketones ( S p )- 170 almost enantiomerically pure (97–99% ee) (Scheme ) . In contrast, the attempted introduction of a functionality E′ at the second ferrocenyl moiety, subsequent to the synthesis of hydrazone ( S , S p )- 169 , is, in addition to being highly diastereoselective (≥96% de), less regioselective, forming ferrocene 171 or 172 or mixtures thereof depending on the nature of the substituent E (Scheme ) . For instance, in case of E = PPh 2 ·BH 3 171 is formed exclusively, whereas for E = C(OH)Ph 2 ferrocene 172 is the only product of this transformation.…”