(−)-2,10-Camphorsultam. A dry,
2-L, three-necked, round-bottomed flask is equipped with a
1.5-in egg-shaped Teflon stirring bar, a
250-mL addition funnel, and a
300-mL Soxhlet extraction apparatus equipped with a mineral oil bubbler connected to an inert-gas source. The flask is charged with
600 mL of dry tetrahydrofuran (THF) (Note
1) and
6.2 g (0.16 mol) of lithium aluminum hydride (Note
2). Into the 50-mL Soxhlet extraction thimble is placed
35.0 g (0.16 mol) of (−)-(camphorsulfonyl)imine (Note
3) and the reaction mixture is stirred and heated at reflux. After all of the
(camphorsulfonyl)imine has been siphoned into the reaction flask (3–4 hr), the mixture is allowed to cool to room temperature. The unreacted
lithium aluminum hydride is cautiously hydrolyzed by dropwise addition of
200 mL of 1 N hydrochloric acid via the addition funnel (Note
4). After the hydrolysis is complete the contents of the flask are transferred to a
1-L separatory funnel, the lower, silver-colored aqueous layer is separated, and the upper layer placed in a
1-L Erlenmeyer flask. The aqueous phase is returned to the separatory funnel and washed with
methylene chloride (3 × 100 mL). After the reaction flask is rinsed with
methylene chloride (50 mL), the organic washings are combined with the
THF phase and dried over anhydrous
magnesium sulfate for 10–15 min. Filtration through a
300-mL sintered-glass funnel of coarse porosity into a
1-L round-bottomed flask followed by removal of the solvent on a
rotary evaporator gives
33.5 g (
95%) of the crude
(−)-2,10-camphorsultam. The crude sultam is placed in a
250-mL Erlenmeyer flask and crystallized from approximately
60 mL of absolute ethanol. The product is collected on a
150-mL sintered-glass funnel of coarse porosity and dried in a
vacuum desiccator to give
31.1 g (
88%) of the pure sultam. A second crop of crystals can be gained by evaporating approximately half the filtrate; the residue is crystallized as above to give
1.4 g (
4%). The combined yield of white crystalline solid, mp
183–184°C,
[α]D −30.7° (CHCl
3, c 2.3) is
92% (Note
5) and (Note
6).