Potassium t-Butoxide-t-Butyl Alcohol Complex


[135329-82-7]  · C8H19KO2  · Potassium t-Butoxide-t-Butyl Alcohol Complex  · (MW 186.37)

(see Potassium t-Butoxide)

Physical Data: white, hygroscopic powder.

Preparative Methods: by removal of the solvent from a solution of t-BuOK in t-BuOH at 50 °C/1 mmHg.1

Wittig Reactions.

When Methylenetriphenylphosphorane is prepared by treating the corresponding phosphonium salt with an organolithium compound in an aprotic solvent, the betaine-lithium ion pairs produced upon reaction with aldehydes and ketones undergo decomposition to alkenes extremely slowly.2 The addition of at least 1.1 equiv of the t-BuOK/t-BuOH complex markedly accelerates the betaine decomposition rate and improves the yields of the products. The solvent-free base is less effective than the complex in these reactions.2 The role of the additive is probably to exchange the lithium cation for the potassium cation, which allows more of the free betaine to be present in equilibrium with the ion pair.2 The t-BuOH proton donor may play an important role as well. Wittig reactions involving methylenetriphenylphosphorane can be run more efficiently by treating the phosphonium salt directly with t-BuOK in t-BuOH or aprotic solvents, e.g. ether, prior to addition of the carbonyl component.3 The proton donor solvent is particularly effective.

Alkene Isomerization Reactions.

Dialkyl 2-propynylamines are efficiently isomerized into the corresponding dialkylamino allenes using the t-BuOK/t-BuOH complex in HMPA (eq 1).4 The use of t-BuOK/DMSO as the base-solvent combination leads to the formation of substantially more of the isomeric 1-dialkylamino alkyne. Nitrogen-substituted allenes are also available from the corresponding 2-propynes by reaction with t-BuOK in THF followed by addition of an equivalent amount of t-BuOH.5

Intramolecular Acyl Transfer Reactions.

The t-BuOK/t-BuOH complex is a useful base for the intramolecular transfer of aliphatic acyl groups in the Baker-Venkataraman reaction for the synthesis of b-diketones (eq 2).6 Variable yields of the b-diketone are obtained when 5-(allyloxy)-2-hydroxyacetophenone is converted to its dianion with Lithium Diisopropylamide (2 equiv) at 0 °C or -78 °C and reacted with crotonoyl chloride.6 The X-ray crystal structure of the t-BuOK/t-BuOH complex has recently been determined.7

Related Reagents.

Potassium t-Butoxide; Potassium Methoxide-Dicyclohexano-18-crown-6.

1. Pritchard, J. G.; Nelson, H. M. J. Phys. Chem. 1960, 64, 795.
2. Schlosser, M.; Christmann, K. F. AG(E) 1964, 3, 636.
3. (a) Fitjer, L.; Quabeck, U. SC 1985, 15, 855. (b) Mander, L. N.; Turner, J. V. TL 1981, 22, 4149. (c) Samuel, S. P.; Niu, T.; Erickson, K. L. JACS 1989, 111, 1429. (d) Shitole, H. R.; Nayak, U. R. IJC(B) 1983, 22, 215.
4. Verkruijsse, H. D.; Bos, H. J. T.; de Noten, L. J.; Brandsma, L. RTC 1981, 100, 244.
5. Broggini, G.; Bruché, L.; Zecchi, G.; Pilati, T. JCS(P1) 1990, 533.
6. Kraus, G. A.; Fulton, B. S.; Woo, S. H. JOC 1984, 49, 3212.
7. Chisholm, M. H.; Drake, S. R.; Naiini, A. A.; Streib, W. E. Polyhedron 1991, 10, 337.

Drury Caine

The University of Alabama, Tuscaloosa, AL, USA

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