Halo sulfoxides

When Z is SOR or SO2R (e.g., a-halo sulfoxides and sulfones), nucleophilic substitution is retarded. The SnI mechanism is slowed by the electron-withdrawing effect of the SOR or SO2R group,and the Sn2 mechanism presumably by the steric effect. 

When chloromethyl p-tolyl sulfoxide (102 R = p-tolyl) is treated with carbonyl compounds (103) and potassium t-butoxide in t-butyl alcohol ether, (p-tolylsulfmyl)oxiranes (104) are directly formed. Chloromethyl methyl sulfoxide (102 R = Me) exhibits the same behavior (Scheme 29). These reactions proceed with high stereoselection at the position a to the sulfmyl group. The stereochemical course proposed for the attack of the carbanion of an a-halo sulfoxide on a carbonyl compound is shown in Figure 4. ... 

The Darzens-type products from a-halo sulfoxides and carbonyl compounds undergo reductive desulfurization by the action of butyllithium. This is a useful synthetic route to various epoxides. Yamakawa and coworkers disclosed a novel asymmetric synthesis of epoxides (109) using optically active 1-chlo-roalkyl p-tolyl sulfoxide (107). This method is most effective when the starting ketones are symmetrical, because only one diastereomer is then formed in the Darzens-type condensation (equation 26). 

Most recent of these is the design of a halo-sulfoxide inhibitor which in the presence of some pyridoxal phosphate dependent enzymes converts to an active allyl sulfenate (360). 

---