Dithiane oxides optical resolution

Bohman and Allenmark resolved a series of sulphoxide derivatives of unsaturated malonic acids of the general structure 228. The classical method of resolution via formation of diastereoisomeric salts with cinchonine and quinine has also been used by Kapovits and coworkers " to resolve sulphoxides 229, 230, 231 and 232 which are precursors of chiral sulphuranes. Miko/ajczyk and his coworkers achieved optical resolution of sulphoxide 233 by utilizing the phosphonic acid moiety for salt formation with quinine. The racemic sulphinylacetic acid 234, which has a second centre of chirality on the a-carbon atom, was resolved into pure diastereoisomers by Holmberg. Racemic 2-hydroxy- and 4-hydroxyphenyl alkyl sulphoxides were separated via the diastereoisomeric 2- or 4-(tetra-0-acetyl-D-glucopyranosyloxy)phenyl alkyl sulphoxides 235. The optically active sulphoxides were recovered from the isolated diastereoisomers 235 by deacetylation with base and cleavage of the acetal. Racemic 1,3-dithian-l-oxide 236... 

Burn at Hoffmann-La Roche chose to couple the two monomeric units via an intramolecular Wadsworth-Emmons reaction rather than lactonization (see Scheme 4.16). Thus dithiane 70, obtained by formylation of the anion derived from 69, underwent a regiospecific 1,3 dipolar cycloaddition with acetonitrile oxide to afford isoxazoline 71. Dibal reduction to the related amino alcohol followed by optical resolution with D-camphorsulfonic acid led to the isolation... 

Interesting examples of optical resolutions include the use of dicarbonyl-rhodium(i) 3-trifluoroacetyl-(li )-camphorate for g.l.c. separation of chiral olefins and of dimeric nickel(ll) bis-(3-trifluoroacetyl-li -camphorate) for an improved separation of chiral epoxides (cf. Vol. 8, p. 8). The resolution of (i /5)-pantoic acid with chiral amines derived from a- and jS-pinene (Vol. 7, p. 43, ref. 420) may signal their more widespread use. 1,3-Dithian 1-oxide has been resolved. ... 

Several approaches to the enantioselective oxidation of sulfides have been reported,61 including enzymatic approaches,62 use of optically pure oxidants,63 and several modifications of the Sharpless epoxidation procedure.63,64 The success of these procedures is somewhat substrate dependent for example, dialkyl sulfides and more complex substrates can give unpredictable results. 1,3-Dithiane itself is oxidized with only ca. 20% ee optically pure DiTOX has, however, been obtained by resolution.65... 

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