[2370-18-5]  · C29H41O2  · Galvinoxyl  · (MW 421.70)

(stable radical and radical scavenger, extensively used as a mechanistic probe for radical chain processes;2 used as an inhibitor to prevent undesired competitive radical paths in reactions3,4)

Physical Data: mp 158-159 °C.

Solubility: sol organic solvents adequate for applications cited.

Form Supplied in: purple crystalline needles.

Handling, Storage, and Precautions: toxicological properties not investigated thoroughly. May be harmful by inhalation, ingestion, or skin absorption. Keep in tightly closed bottles away from oxygen in a refrigerator. Use in a fume hood.

Galvinoxyl is a stable phenoxy radical5 which reacts with other radicals at a rate constant near the diffusion-controlled limit (eq 1). Scavenging of radicals leads to decolorization and colorimetric determination is a way of estimating the efficiency of radical formation. Galvinoxyl has been widely used as a probe in the study of organometallic6 and radical2 reaction mechanisms. A compilation of earlier work can be found in Kochi's monographs.2,6

In a classical example, the inhibition of the addition of alkyl boranes to a,b-unsaturated carbonyl compounds was interpreted to mean a radical pathway for this reaction.7 Other reactions that have been investigated recently, include addition of trialkylaluminum to enones,8 RuII-catalyzed Kharasch-type additions of carbon tetrachloride to alkenes,9 2,3-dichloropropene-mediated homocoupling of aryl Grignards,10 SRN1 reactions,11 carbonyl additions of acyltin reagents, and radical polymerization of styrene.

A recent example of the use of galvinoxyl to affect the course of a reaction is in the chemoselective reduction of the carbonyl group of a-bromo ketones with dibutyltin dihydride.3 Without the the radical inhibitor the reduction of the a-bromo group took place.

A more general use of free radical inhibitors in organic synthesis is illustrated by the use of galvinoxyl in the synthesis of (R)-(+)-cyclohex-3-enecarboxylic acid via a Diels-Alder reaction. The major complication arising from the Ethylaluminum Dichloride-mediated polymerizations (presumably through a radical mechanism) is suppressed by galvinoxyl (eq 2).4

1. Fieser, L. F.; Fieser, M. FF 1967, 1, 409.
2. Kochi, J. K. Free Radicals; Wiley: New York, 1973.
3. Shibata, I.; Nakamura, K.; Baba, A.; Matsuda, H. TL 1990, 31, 6381.
4. Thom, C.; Kocienski, P.; Jarowicki, K. S 1993, 475.
5. For a series of earlier classical papers that deals with galvinoxyl, see: Coppinger, G. M. JACS 1957, 79, 501; Kharasch, M. S.; Joshi, B. S. JOC 1957, 22, 1435; Bartlett, P. D.; Rüchardt, C. JACS 1960, 82, 1756; Greene, F. D.; Adam, W.; Cantrill, J. E. JACS 1961, 83, 3461; Bartlett, P. D.; Funahashi, T. JACS 1962, 84, 2596; Bartlett, P. D.; Gontarev, B. A.; Sakurai, H. JACS 1962, 84, 3101; Greene, F. D.; Adam, W. JOC 1963, 28, 3550; Schuler, R. H. J. Phys. Chem. 1964, 68, 3873.
6. Kochi, J. K. Organometallic Mechanisms and Catalysis; Academic: New York, 1978.
7. Kabalka, G. W.; Brown, H. C.; Suzuki, A.; Honma, S.; Arase, A.; Itoh, M. JACS 1970, 92, 710. See also: Arase, A.; Masuda, Y. CL 1975, 419.; Nozaki, K.; Oshima, K.; Utimoto, K. T 1989, 45, 923.
8. Kabalka, G. W.; Daley, R. F. JACS 1973, 95, 4428.
9. Matsumoto, H.; Nakano, T.; Nagai, Y. TL 1973, 5147.
10. Cheng, J. W.; Luo, F. T. TL 1988, 29, 1293.
11. Creary, X.; Sky, A. F.; Phillips, G. JOC 1990, 55, 2005. For a recent application in the investigation of the mechanism of substitution of aromatic nitro groups, see: Denney, D. B.; Denney, D. Z.; Perez, A. J. T 1993, 49, 4463.

T. V. (Babu) RajanBabu

The Ohio State University, Columbus, OH, USA

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