Improvements in the Synthesis of a Key α-tocopherol, Intermediate[sbnd] (s)-(−)-3,4-Dihydro-6-Hydroxy-2,5,7,8-Tetramethyll-2H-1-Benzopyran-2-Acetic Acid

References

• Scott , J. W. , Bizzarro , F. T. , Parrish , D. R. and Saucy , G. 1976 . Helv. Chim. Acta , 59 : 290
   PubMed Web of Science ®Google Scholar
• Cohen , N. , Scott , J. W. , Bizzarro , F. T. , Lopresti , R. J. , Eichel , W. F. and Saucy , G. 1978 . Helv. Chim. Acta , 61 : 837
   Web of Science ®Google Scholar
• Cohen , N. , Eichel , W. F. , Lopresti , R. J. , Neukom , C. and Saucy , G. 1976 . J. Org. Chem. , 41 : 3505 – 3512 .
   PubMed Web of Science ®Google Scholar
• Chan , K.-K. and Saucy , G. 1977 . J. Org. Chem. , 42 : 3828
   Web of Science ®Google Scholar
• Chan , K.-K. , Specian , A. C. Jr. and Saucy , G. 1978 . J. Org. Chem. , 43 : 3435
   Web of Science ®Google Scholar
• Cohen , N. , Scott , C. G. , Neukom , C. , Lopresti , R. J. , Weber , G. and Saucy , G. 1981 . Helv. Chim. Acta , 64 : 1158
   Web of Science ®Google Scholar
• Cohen , N. , Lopresti , R. J. and Neukom , C. 1981 . J. Org. Chem. , 46 : 2445 For recent related studies involving a homologous approach to (2R,4′R,8′R)-α-tocopherol (C14-chroman + C15-side chain) see a.;b. N. Cohen, R. J. Lopresti, and G. Saucy, J. Am. Chem. Soc. 101, 6710 (1979);c. R. Barner and M. Schmid, Helv. Chim. Acta 62, 2384 (1979);d. J. M. Akkerman, H. de Koning, and H. O. Huisman, Heterocycles 15, 797 (1981)
   Web of Science ®Google Scholar
• For example, racemic acid 4 can be obtained in ca. 70% overall yield starting from trimethylhydroquinone
   Google Scholar
• Di Blase , S. A. , Lipisko , B. A. , Haag , A. , Wolak , R. A. and Gokel , G. W. 1979 . J. Org. Chem. , 44 : 4640 cf. and references cited therein
   Web of Science ®Google Scholar
• H , Acid 4 could also be obtained by the same sequence, starting from 3,4-dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-2,6-diol11 although the overall yield was variable (50–70%). Surprisingly, treatment of 6-benzyloxy-3,4-dihydro-2,5,7,8-tetramethyl-2-1-benzopyran-2-ol2 with KOH-acetonitrile led to a complex mixture containing only a small amount of the desired 6-benzyloxy analogue of 3 (observation of R. J. Lopresti)
   Google Scholar
• John , W. and Schmeil , M. 1939 . Chem, Ber. , 72 : 1653
   Google Scholar
• Scott , J. W. , Cort , W. M. , Harley , H. , Parrish , D. R. and Sauey , G. 1974 . J. Am. Oil Chem. Soc. , 51 : 200
   Web of Science ®Google Scholar
• As an additional example, (R)-(+)-6-benzyloxy-3,4-dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-2-acetic acid2 could be racemized and recovered in 98% yield using this procedure
   Google Scholar
• chiral , 4 Efforts to effect asymmetric induction by thermodynamic equilibration of diastereomeric derivatives of chroman-2-acetic acids (e.g., base catalyzed equilibration of esters derived from alcohols) have not afforded viable alternatives to the resolution-recycling process described herein
   Google Scholar