Synthesis of Chiral Sulfinic Acids: Sodium(1S-exo)-2-Bornanesulfinate

Preparation and stereochemical integrity of certain thioesters of 2-arylpropionic acids and related compounds

“…Quantities of (1S,4S)-exo-2-bornanethiol (4) could be prepared in good quantity and purity from commercially avail-able (1S,4S)-endo-2-borneol (1) by either of the two routes shown in Figure 2. (1S,4S)-exo-2-Bornyl-isothiouronium ptoluenesulphonate (2) was prepared as described by Blanco et al (1990). Hydrolysis of the thiouronium salt 2 to thiol 4 was more conveniently achieved by treatment with potassium metabisulphite in aqueous base (Cai et al 2002) than by the method originally described by Blanco et al (1990).…”

“…(1S,4S)-exo-2-Bornyl-isothiouronium ptoluenesulphonate (2) was prepared as described by Blanco et al (1990). Hydrolysis of the thiouronium salt 2 to thiol 4 was more conveniently achieved by treatment with potassium metabisulphite in aqueous base (Cai et al 2002) than by the method originally described by Blanco et al (1990). Alternatively, thiol 4 could be obtained by application of a method described by Rollin (1986) as follows.…”

“…The solvent was removed under vacuum and the resultant material was re-crystallised from the minimum amount of hot water to afford the title compound (4) as a colourless crystalline solid (4.08 g, 80%, 24-26 C, lit. mp 24-26 C (Blanco et al 1990)). max /cm À1 ( Zinc N, N-dimethyldithiocarbamate (7.24 g, 23.7 mmol) was added to a stirred solution of triphenylphosphine (33.0 g, 126 mmol) and (1S,4S)-endo-2-borneol (1) (6.10 g, 39.6 mmol) in anhydrous toluene (50 mL).…”

“…We were also interested in the possibility of such systems forming the basis for bio-mimetic dynamic kinetic resolutions of 2-APA and related thioesters. Nonracemic exo-2-boranethiol (4) was selected for conjugation to the 2-APAs and related compounds as this thiol was reportedly obtainable in the chiral non-racemic form from either chiral non-racemic camphor (Dagonneau et al 1973) or borneol (Blanco et al 1990), and as the bornyl 1,7,7-trimethylbicyclo[2.2.1]heptan ring system would constitute a robust chiral auxiliary and stereochemical label with no possibility of itself undergoing inversion of stereocentres. In addition, the resulting thioesters would be non-polar products that could be easily purified and handled.…”

Monoterpenoids

“…The hydroxythiol (286) can be converted into a-sulfinyl ketones which are then reduced with high diastereosele~tivity.~~~ (-)-Isoborneol (264) can be converted, via its p-toluenesulfonate, into the chiral sulfinic acid salt (287). 306 28.5% at C-3. The reagent also works well with enolizable p-diket~nes.~O* Asymmetric syntheses which utilize monoterpenoids as chiral auxiliaries are not always successful.…”