[603-35-0]  · C18H15P  · Triphenylphosphine-Iodoform-Imidazole  · (MW 262.30) (CHI3)

[75-47-8]  · CHI3  · Triphenylphosphine-Iodoform-Imidazole  · (MW 393.72) (imidazole)

[288-32-4]  · C3H4N2  · Triphenylphosphine-Iodoform-Imidazole  · (MW 68.09)

(deoxygenation of vicinal diols and epoxides to form alkenes;1 particularly useful in the synthesis of unsaturated sugars)

Physical Data: see Triphenylphosphine, Iodoform, and Imidazole.

Preparative Method: Bessodes et al.1 reported that treatment of cis- or trans-1,2-diols with 4 equiv of triphenylphosphine, 2 equiv of iodoform and 2 equiv of imidazole in refluxing toluene (typically for 1 h) effects elimination of the vicinal diols to form the corresponding alkene.

General Discussion.

Methods for the conversion of vicinal diols to alkenes have found utility in organic synthesis, particularly in the synthesis of unsaturated or dideoxy sugars, and a number of alternative methods have been developed.2 The use of a mixture of triphenylphosphine, iodoform, and imidazole to accomplish the reductive elimination of vicinal diols was introduced by Bessodes et al.1 For example, the cis- and trans-1,2-diols in eq 1 are converted to the corresponding unsaturated sugars in moderate to good yields, the better yields being obtained from the trans-isomers. The methodology was introduced as an alternative to the methods of Garegg and Samuelsson which employ a mixture of triphenylphosphine-Iodine-imidazole3 or a mixture of Triphenylphosphine-2,4,5-Triiodoimidazole.4

Nagarajan and Rao5 used the triphenylphosphine-iodoform-imidazole reagent for the reductive elimination of a xylose-derived benzoate in 85% yield (eq 2). The procedure was used by Wee6 for the reductive elimination of a methyl glucoside derivative bearing both benzoyl and t-butyldiphenylsilyl protecting groups. The dehydro-sugar is formed in 94% yield (eq 2). In this latter case the corresponding dimesylate derivative is reported7 to desilylate under an alternative set of reductive elimination conditions, the Tipson-Cohen method (NaI, Zn, DMF).8 Reported attempts to apply the method to furanoside substrates were unsatisfactory.9,10

The methodology may have some application in nucleoside synthesis. Chu and co-workers11 found that treatment of a dimethylpseudouridine derivative affords the dideoxycytidine analog in modest yield (40%) (eq 3). In this case the authors found that Tri-n-butylstannane reduction of the corresponding dimethyl xanthate is superior, proceeding in an overall 76% yield for the two steps. Halmos and co-workers12 used the procedure in the preparation of certain keto nucleosides with greater success. Deoxygenation affords the theophylline derivative in 70% yield (eq 4). The authors found this method to be superior to deoxygenation via the thionocarbonate or the 1-dimethylamino(methylene) acetal.

Lichtenthaler and co-workers13 found that the triphenylphosphine-iodoform-imidazole reagent system is also effective in the deoxygenation of an epoxide. The epoxide derived from fructose is converted to the 3,4-unsaturated dihydropyran in 84% yield (eq 5), although unlike the reported conversions of diol substrates, reaction of the epoxide required two days in refluxing toluene.

Related Reagents.


1. Bessodes, M.; Abushanab, E.; Panzica, R. P. CC 1981, 26.
2. Block, E. OR 1984, 30, 457.
3. Garegg, P. J.; Samuelsson, B. S 1979, 10, 469.
4. Garegg, P. J.; Samuelsson, B. S 1979, 10, 813.
5. Rao, M. V.; Nagarajan, M. JOC 1988, 53, 1184.
6. Wee, A. G.; Zhang, L. SC 1993, 23, 325.
7. Pelyvas, I.; Lindhorst, T.; Thiem, J. LA 1990, 761.
8. Tipson, R. S.; Cohen, A. Carbohydr. Res. 1965, 1, 338.
9. Lacourt-Gadras, B.; Grignon-Dubois, M.; Rezzonico, B. Carbohydr. Res. 1992, 235, 281.
10. Martin, O. R.; Rafka, R. J.; Szarek, W. A. Carbohydr. Res. 1989, 185, 77.
11. Doboszewski, B.; Chu, C. K.; Halbeek, H. JOC 1988, 53, 2777.
12. Halmos, T.; Komiotis, D.; Antonakis, K. Carbohydr. Res. 1986, 156, 256.
13. Lichtenthaler, F. W.; Doleschal, W.; Hahn, S. LA 1985, 2454.

James M. Takacs

University of Nebraska, Lincoln, NE, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.