REFERENCES
- U.S. patent 5,952,519 . which covers this route to canthaxanthin, has been issued (Sept. 14, 1999) to Loyola University Chicago.
- Britton , G. , Liaaen-Jensen , S. and Pfander , H. 1996 . Carotenoids Volume 2: Synthesis Basel : Birkhauser-Verlag .
- Haxo , F. 1950 . Bot. Gaz. , 112 : 228
- Petracek , F.J. and Zechmeister , L. 1955 . J. Am. Chem. Soc. , 78 : 1427
- Rosenberger , M. , McDougal , P. , Saucy , G. and Bahr , J. 1979 . Pure & Appl. Chem. , 51 : 871
- U.S. patent 4,000,198 . Dec. 28, 1976 . which is cited in Chem. Abstr. 1977,87, 39706f.
- Rosenberger , M. , McDougal , P. and Bahr , J. 1982 . J. Org. Chem. , 47 : 2130
- Bertram , J.S. 1994 . Pure & Appl. Chem. , 66 : 1025
- Eur. Pat. Appl. 17,800 . Oct. 29, 1980 . which is cited in Chem. Abstr.1981,94,174463j.
- Becher , E. , Albrecht , R. , Bernhard , K. , Leuenberger , H.G.W. , Mayer , H. , Muller , R.K. , Schuep , W. and Wagner , H.P. 1981 . Helv. Chim. Acta , 64 : 2419
- For a more economical route to convert β-ionone to diketone . Japanese patent 81,161,370 . Dec. 11, 1981 . which is cited in Chem. Abstr.1982,96,199941t.
- Purchased as a 0.50 Msolution in tetrahydrofuran from Aldrich Chemical Co., Milwaukee,WI
- Mal’kina , A.G. , Brandsma , L. , Vasilevsky , S.F. and Trofimov , B.A. 1996 . Synthesis , : 589
- Johnson , W.S. and Schneider , W.P. 1950 . Org. Synth. , 30 : 18
- Use of a larger excess of ethynylmagnesium chloride afforded a product mixture containing as much as 50% of diyne-diol 4. However, after subsequent treatment of the crude ethynylation product mixture with powdered NaOH at 20°C, the overall yield of desired keto alkynol 3 was still >75%.
- None of the starting dione 2, characterized by a singlet at δ 1.22 (two methyls bonded to C-4), was detected by proton NMR analysis.
- The addition of a second portion of powdered NaOH and subsequent stirring at 20°C for an additional 6 h is necessary only if the crude ethynylation product contains a substantial amount (e.g., 20%) of diyne-diol 4.