Sulfinyl chloride, reaction with Grignard reagents

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

Asymmetric a-alkylation of amines was achieved applying an immobilized chiral sulfonamide (Scheme 12.29) [13, 40]. To synthesize auxiliary 76, a tertiary alcohol (73) was converted into Grignard reagent 74. Addition of sulfur dioxide and subsequent chlorination furnished the sulfinyl chloride 75. Reaction with (S)-2-amino-l,l,2-triphenylethanol, followed by reduction, hydroboration and... 

---