Dienone–phenol rearrangement

The dienone–phenol rearrangement^[1] is a reaction in organic chemistry first reported in 1921 by Karl von Auwers and Karl Ziegler. A common example of dienone–phenol rearrangement is 4,4-disubstituted cyclohexadienone [de] converting into a stable 3,4-disubstituted phenol in presence of acid. A similar rearrangement is possible with a 2,2-disubstituted cyclohexadienone to its corresponding disubstituted phenol. Usually this type of rearrangement is spontaneous unless a dichloromethyl group is present at the 4th position or the process is otherwise blocked.^[2]

Dienone–phenol rearrangement of 4,4-disubstituted cyclohexadienone into 3,4‐disubstituted phenol

Dienone–phenol rearrangement of 2,2-disubstituted cyclohexadienone

Reaction mechanism

The reaction mechanism of 4,4-disubstituted cyclohexadienones to 3,4-disubstituted phenol is illustrated here.

 

The migration tendency for the two different groups (R) present at either 4,4 position or 2,2 position can be determined by comparing the relative stability of the intermediate carbocation formed during rearrangement. In case of acid-promoted conditions, some relative migration tendencies are: COOEt > phenyl (or alkyl);^[3] phenyl > methyl;^[4] vinyl > methyl;^[5] methyl > alkoxy and alkoxy > phenyl.^[6] In some cases such as allyl and benzyl group, the actual rearrangement might happen through the Cope rearrangement.^[7][8] Apart from acid catalysis, the dienone–phenol rearrangement is also possible in presence of base. The dienone–phenol rearrangement has been used in the synthesis of steroids,^[9] anthracenes,^[10] and phenanthrenes.^[11]

References

1. Li, Jie Jack (2021). "Dienone–Phenol Rearrangement". Name Reactions. pp. 176–178. doi:10.1007/978-3-030-50865-4_46. ISBN 978-3-030-50864-7.
2. Comprehensive Organic Name Reactions and Reagents - "Dienone–Phenol Rearrangement". John Wiley & Sons. 15 September 2010. p. 900. doi:10.1002/9780470638859.conrr193. ISBN 9780470638859.
3. Kagan, Jacques; Agdeppa, Dalmacio A.; Singh, S. P.; Mayers, David A.; Boyajian, Charles; Poorker, Carol; Firth, Bruce E. (July 1, 1976). "Molecular rearrangements with ethoxycarbonyl group migrations. 1. The rearrangement of epoxides". J. Am. Chem. Soc. 98 (15): 4581. doi:10.1021/ja00431a042.
4. Arnold, Richard T. (May 1, 1949). "The Dienone–Phenol Rearrangement. II. Rearrangement of 1-Keto-4-methyl-4-phenyl-1,4-dihydronaphthalene". J. Am. Chem. Soc. 71 (5): 1781. doi:10.1021/ja01173a071.
5. Marx, John N.; Hahn, Young Sook Paik (November 4, 1987). "Acid-Catalyzed Migration of the Vinyl Substituent in the Dienone–Phenol Rearrangement". J. Org. Chem. 53 (12): 2866. doi:10.1021/jo00247a046.
6. "Dienone–Phenol Rearrangement of 2-Phenyl-o-quinolacetate". J. Am. Chem. Soc. 71 (5): 1781. May 1, 1949. doi:10.1021/jo01090a603.
7. Miller, Bernard. (1970). "Acid-Catalyzed Rearrangements of Cyclohexa-2,4-dien-l-ones. Competitive [1,2] and [1,5] Migrations". Journal of the American Chemical Society. 92 (2): 432. doi:10.1021/ja00705a633.
8. Bernard, Miller (1965). "Dienone–Phenol Rearrangements of 6-Allylcyclohexa-2,4-dienones and 4-Allylcyclohexa-2,5-dienones. Acid Catalysis of Cope Rearrangements1". Journal of the American Chemical Society. 87 (22): 5115. doi:10.1021/ja00950a024.
9. Djerassi, Carl; Scholz, Caesar R. (1948). "The Preparation and Dienone–Phenol Rearrangement of 2-Bromo-1,4-androstadien-17-ol-3-one 17-Hexahydrobenzoate". J. Am. Chem. Soc. 70 (5): 1911–1913. doi:10.1021/ja01185a075. PMID 18861812.
10. Marvell, Elliot N.; Geiszler, Adolph O. (March 1, 1952). "The Rearrangement of Some Disubstituted Cyclic Ketones: An Unusual Dienone–Phenol Rearrangement". J. Am. Chem. Soc. 74 (5): 1259. doi:10.1021/ja01125a035.
11. Arnold, Richard T.; Buckley, Jay S.; Dodson, R. M. (1950). "The Dienone–Phenol Rearrangement. III. Rearrangement of 1-Keto-4,4-tetramethylene-1,4-dihydronaphthalene". Journal of the American Chemical Society. 72 (7): 3153. doi:10.1021/ja01163a095.