Sulfoxides ortholithiation

In 1994, the same authors reported the synthesis of corresponding oxazolines tethered to sulfoxides by ortholithiation of the parent 2-phenyl oxazoline with butyllithium followed by addition of either (5)- or (/ )-/ -tolylmenthyl-sulfinate. Applied as ligands in the test reaetion, these diastereomerie ligands gave very different results, as shown in Seheme 1.25, thus demonstrating the... 

In sulfoxides, sulfur s weak acidifying effect is enhanced, and the oxygen atom introduces a powerful coordination effect in contrast with sulfides, sulfoxides are very powerful directors of both ortholithiation and a-lithiation. Ortholithiation is possible with aryl sulfoxides lacking an a-proton, but since sulfoxides suffer from the disadvantage of being electrophilic at sulfur, diaryl sulfoxides must be lithiated with lithium amide bases rather than... 

Sulfoxide removal using sulfoxide-lithium exchange (see section 3.3.3) is also effective.213 It was employed in tandem with a sulfoxide-directed stereoselective ortholithiation of the ferrocene 242214 215 in this synthesis of the phosphine ligand 243.216 Ferrocene lithiation is discussed further in section 2.3.4.2. 

Sulfones are similar in some ways even more acidifying, and with a powerful ability to coordinate, but less likely to be attacked at S. As with sulfoxides, lithiation a to S competes, and ortholithiation is useful only with sulfones lacking a-protons.141 After lithiation, the removal of sulfones can sometimes be accomplished by transition metal-catalysed reduction or substitution 144 143... 

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