Oxidative Imination of Sulfur Compounds

The oxidative imination of sulfides and sulfoxides via nitrene transfer processes leads to N-substituted sulfilimines and sulfoximines. This reaction is interesting as chiral sulfoximines are efficient chiral auxiliaries in asymmetric synthesis, a promising class of chiral ligands for asymmetric catalysis and key intermediates in the synthesis of pseudopeptides [169]. However, very few examples of such iron-catalyzed transformations have been described. 

Bach and Korber reported in 1998that iron(I I) chloride could be used in combination with tert-butyloxycarbonyl azide (BocN3) for nitrene transfer to sulfides and sulfoxides [170], Whereas usually 1 equiv. of FeCl2 was employed in the imination of sulfoxides, catalytic amounts of this iron salt (25mol%) could also be applied (Table 3.13). 

The imination of sulfides with this catalytic system has been proved to proceed more readily than for the corresponding sulfoxides [169]. Thus, sulfilimines can be obtained in moderate to good yields, especially when acetylacetone or DMF is added (Table 3.14). 

The reaction proceeds in a stereospecific manner, with retention of configuration at sulfur. It thereby constitutes an alternative access to enantiopure sulfoximines from the corresponding optically active sulfoxides. The deprotection of the N-nosyl 

In analogy with the corresponding known iron-oxo complexes, an iron nitrene complex (L Fe=NR) has been proposed as a reactive intermediate in these processes for both catalytic systems described above [176]. 

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