Phenylsulfinyl glycals

Expanding upon the lithiation of 2-phenylsulfinyl glycals, Schmidt and Dietrich [33] effected coupling reactions with benzaldehyde (Scheme 7.59). As illustrated, this reaction resulted in an approximate yield of 86%. An important observation is the induction of stereochemistry at the newly formed center with a diastereomeric ratio of approximately 4 1. 

The 2-phenylsulfinyl glucal 111 is available from glucal 110 by addition of phenylsulfenyl chloride, DBU elimination and oxidation. The Cl-substituted glycal 113, obtained by addition of the lithium reagent 112 to aldehydes, is transformed to a 8-D-C-glucosyl derivative 114 by reductive removal of the phenylsulfinyl group with Raney nickel and stereoselective hydration of the C/C double bond by hydroboration-oxidation. 

Continuing with the direct metallation of glycals, 2-phenylsulfinyl derivatives have found utility. Their formation and subsequent lithiation, shown in Scheme 3.1.4, is accomplished on reaction of glycals with phenylsulfenyl chloride under basic conditions. Subsequent oxidation with mCPBA yields the sulfinyl compound ready for lithiation on treatment with lithium diisopropylamide. Advantageous to the formation of this species is the stabilization of the anion by chelation of the sulfoxide to the metal. This procedure reported by Schmidt, et al.,5 was utilized in the preparation of C-disaccharides, discussed in Chapter 8. 

Schmidt and coworkers have described the direct lithiation at the C-2 atom of the 1-phenylsulfinyl substituted glycal (46) using LDA followed by reaction with C-electrophiles to give products such as (47) (Scheme 5.15) [51]. 

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