反应详情

A mixture of 1.29 g (3.41 mmoles) of rac-3,4-dihydro-2,5,7,8-tetramethyl-6-methoxy-2H-1-benzopyran-2-ylpropanedioic acid diethyl ester, 1.68 g of potassium hydroxide, and 75 ml of 9:1 parts by volume ethylene glycol-water mixture was stirred and refluxed for 6 hours. The resulting mixture was poured on ice and extracted with ether (the ether extract was discarded). The aqueous solution was acidified with 3N HCl and the preciptated acid was extracted 3 times with ether. The combined ether extracts were washed with brine, dried (MgSO4), filtered and concentrated in vacuo. Purification of the residue by preparative thick layer chromatography gave 0.72 g (75.9%) of rac.-3,4-dihydro-6-methoxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-acetic acid, as a colorless solid, mp 96°-98° C. Demethylation using the procedure of example 14 gives rac.-3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-acetic acid which can be converted to alpha-tocopherol as described in Helv. Chim. Acta. 59, 290 (1976).

1. temperaturerefluxed for 6 hours
2. additionThe resulting mixture was poured on ice
3. extractionextracted with ether (the ether
4. extractionextract
5. extractionthe preciptated acid was extracted 3 times with ether
6. washThe combined ether extracts were washed with brine
7. dry with materialdried (MgSO4)
8. filtrationfiltered
9. concentrationconcentrated in vacuo
10. customPurification of the residue by preparative thick layer chromatography