Metallocene Sulfoxides as Precursors of Metallocenes with Planar Chirality

Abstract

The preparation of metallocene sulfoxides and their ortho-diastereoselective functionalization are described. The applications of enantiopure 1,2-and 1,3-disubstituted metallocenes are reviewed, with special emphasis on the preparation of ligands for asymmetric catalysis. The sulfoxide functionality is a useful, traceless, chiral diastereoselective orthodirecting group, as explained in the article. It allows one to synthesize a wide range of enantiopure metallocenes with planar chirality and predictible configuration. Most of the examples are related to the ferrocene area.

Two aspects of the desymmetrization of selected prochiral aromatic or vinylic dihalides: enantioselective halogen–lithium exchange and prochiral recognition in chiral liquid crystals

“…33,34 We have thus clearly proved that the pro-R iodide in 4 had been exchanged preferentially when (À)-sparteine is the chiral auxiliary (Scheme 7). 35 It is interesting to notice that the use of two or more equivalent of n-BuLi does not yield to the double iodide-lithium exchange reaction in ferrocene and norbornadiene series.…”

The diastereoselective ortho-lithiation of Kagan’s ferrocenyl acetal. Generation and reactivity of chiral 2-substituted ferrocenecarboxaldehydes

“…17 The present review focuses on the different facets of ferrocenyl acetal 3, since its applications are limited not only to asymmetric catalysis but also to material science and biology.…”

Improved Syntheses of 1,2‐Disubstituted Ferrocenes

“…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 . According to our interest in 1,2‐dehydroferrocene (“ferrocyne”) and 1,2,1′,2′‐tetradehydroferrocene (“ferrocenediyne”) we recently reported the formation of 2‐(trifluoromethylsulfonyl)ferrocenols by unprecedented anionic thia‐Fries rearrangements of ferrocenyl triflates under mild reaction conditions in high yields instead of the desired elimination products , .…”