A Facile and Efficient Method for Monoketalization of 1,4-Cyclohexanedione

References

• Kamenka , J.-M. , Geneste , P. and El Harfi , A. 1983 . Bull. Soc. Chim. Fr. , II : 87 For the most recent synthesis of monoketal 1a, see:
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• Hyatt , J. A. 1983 . J. Org. Chem. , 48 : 129 For previous syntheses of monoketal derivatives of 1, 4-cyclohexanedione, see: and references therein
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• For a discussion of the problems encountered during previous syntheses of monoketal 1a, see reference 2
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• Milwaukee, WI : Available from Aldrich Chemical Co. .
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• Babler , J. H. and Coghlan , M. J. 1979 . Tetrahedron Lett. , : 1971
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• Babler , J. H. and Moy , R. K. 1979 . Synth. Commun. , 9 : 669
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• Provided that the diol is present in excess in the aqueous reaction mixture, the quantity of 1,4-cyclohexanedione subjected to monoketalization is not critical. Thus the yield and purity of monoketal 1b did not vary from the data reported in this communication when experiments were conducted using either 0.50 g or 2.0 g of the dione with no changes in the quantities of the other reagents. In sharp contrast, however, use of more diol or sulfuric acid, while maintaining the total volume of the aqueous layer constant (240–245 mL, after dissolving the diol), led to increased formation of the undesired bisketal
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• Subsequent to the completion of the ketalization reaction, the excess diol can be recovered by continuous extraction of the aqueous layer with ether
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• No ketal could be obtained when a mixture of 2,2-dimethyl-1,3-propanediol and 1,4-cyclohexanedione was heated in hexane at reflux for several hours. However, trace amounts of sulfuric acid may be carried over during the course of the extraction, thereby catalyzing further ketalization
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• The starting dione had an NMR spectrum (CDCl3 solution) which was characterized by an 8H singlet at 2.74. The corresponding absorptions (cyclohexane ring H's) for the bisketal and monoketal were 1.87(s) and 2.31 (very broad multiplet) respectively
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• If 4:1 (v/v) H20: brine was used in this step of the purification process, small amounts of monoketal 1b were lost – as evidenced by a lower monoketal: bisketal ratio subsequent to the aqueous washes
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• The sole impurity was the undesired bisketal
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