Ferrocenyl sulfoxides

Similar stereo specific conversions of chiral ferrocenyl sulfoxides 30 to ferro-cenyl sulfoximines 31, either with [(tosylimino)iodo]benzene or its nosylate analog 32 have been reported (Scheme 18) [41], including the synthesis of a planar-chiral ferrocenyl sulfoximine [42]. 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

I. 10). Thus aryl ferrocenyl sulfoxides (36) (>99% ce) were prepared by CHP oxidation of (35), in presence of the titanium complex prepared under strictly defined conditions [72]. Similar oxidation was used by Gibson, nee Thomas, et al. for the preparation of sulfinyl substituted tricarbonyl (T -arene) chromium(O) complexes (38), with ee s of up to 86% [73]. It is remarkable that the conditions are mild enough to avoid overoxidation and destruction of the tricarbonylchromium moiety. 

Rebidre, F., Ri t, O. , Ricard, L., Kagan, H. B. (1993) Asymmetric synthesis and hi ly diastereoselective ortho-lithiation of ferrocenyl sulfoxides. Application to the synthesis of ferrocenyl derivatives with planar chirality., Angew. Chem. Int. Ed Eng. 32,568-570. 

Thomas and co-workers59 have described the oxidation of methylthio-sub-stituted tricarbonyl-(ri6-arene)chromium(0) complex 26 with CHP in the presence of Ti(0-j-Pr)4/DET/H20 combination to give the corresponding sulfoxide in 90-95% ee, in a similar approach to that used by Kagan60 for the oxidation of aryl ferrocenyl sulfide 28 (Scheme 9). 

The high degree of diastereoselection in the oxidation of chiral ferrocenyl vinyl selenides was supported by the oxidation of the chiral p-tolyl ferrocenyl sulfide, instead of the selenide, with MCPBA at low temperature. Thus, an almost complete diastereoselective oxidation occurred either at - 20 °C or - 78 °C to give the corresponding chiral sulfoxide (Scheme 11). On the other hand, the oxidation of p-tolyl 1 -(M,M-dimethylamino)ethylphenyl sulfide with MCPBA afforded... 

Figure 3.2 Ferrocenyl ligand (1), Sulfoxide (2) and mode of complexation (3).

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