[95970-99-3]  · C16H37ClO2Sn2  · 3-Chloro-1-hydroxytetrabutyldistannoxane  · (MW 534.40)

(mild Lewis acid catalyst for urethane formation,3 transesterification,4c esterification,4c acetalization,6 deacetalization,7 and deprotection of silyl ethers7)

Alternate Name: CHTD.

Physical Data: mp 107-115 °C.

Solubility: insol H2O, cold MeOH; sol most organic solvents.

Preparative Methods: a mixture of dibutyltin oxide (14.9 g, 60 mmol) and dibutyltin dichloride (6.07 g, 20 mmol) in 95% ethanol (200 mL) is heated under reflux. After 6 h the transparent solution is concentrated to give a white powder. This is pulverized, then exposed to ambient atmosphere overnight. The exposure to air converts partially formed ethoxydistannoxane to the corresponding hydroxydistannoxane. Recrystallization of the crude product from hot hexane affords pure 3-chloro-1-hydroxytetrabutyldistannoxane (15.1 g, 72%).

Handling, Storage, and Precautions: is extremely stable in air and to moisture and thus can be handled and stored in the open air. Because this compound is not volatile, it is virtually nontoxic under the usual conditions.

Urethane Formation.

CHTD catalyzes the reaction between isocyanates and alcohols much more efficiently than conventional organotin catalysts, and polyurethane formation from tolylene diisocyanate and poly(oxypropylene triol) is effected by 5 × 10-4 mol of CHTD per mol of -NCO.2 The mechanism of the catalysis has been disclosed.3


Transesterification is catalyzed by CHTD (eq 1). The reaction is quite simple: a mixture of an ester and an alcohol is heated under reflux in toluene in the presence of the catalyst. The catalyst is surprisingly active; even 0.05 mol % catalyst is effective. The reaction proceeds under almost neutral conditions, and thus various functional groups remain intact during the reaction. Notably, b-keto esters are transesterified smoothly (eq 2), and transesterification of one of the acetoxy groups in 1,n-diol diacetates is realized in a highly selective manner (eq 3). The unique reactivities are ascribed to the template effects of the dimeric formulation shown in (1).

Esterification of Carboxylic Acids.4c,5

The CHTD catalyst is effective not only for intermolecular esterification of carboxylic acids (eq 4) but also macrolactonization of o-hydroxy acids (eq 5). Most significantly, the distannoxane-catalyzed esterification is free from the reverse reaction (hydrolysis). Simply heating the two reactants completes the reaction without the use of a Dean-Stark apparatus. The absence of hydrolysis is a consequence of the double-layered structure of CHTD, whose hydrophobic surface butyl groups prevent the water from approaching the catalytically important core sites, i.e. the tin atoms.

Acetalization of Carbonyls.6

Exposure of carbonyls to ethylene glycol in refluxing benzene, toluene, or methanol in the presence of a catalytic amount of CHTD affords the corresponding acetals in high yields. Mild reaction conditions allow facile preparation of products that are otherwise difficult to obtain. Ketones are acetalized more slowly than aldehydes. However, addition of an equivalent amount of aldehyde accelerates the reaction dramatically. A unique transcarbonylation mechanism is responsible for this acceleration.

Deprotection of Acetals and Silyl Ethers.7

Acetals are converted to parent carbonyls by treating with 1 mol % of CHTD in diethylene glycol dimethyl ether or dioxane-water at 100 °C. THP ethers are deprotected when heated in methanol or THF-H2O under catalysis by CHTD. Silyl ethers are also converted to alcohols under analogous conditions.

1. Okawara, R.; Wada, M. JOM 1963, 1, 81. Otera, J. In Advances in Detailed Reaction Mechanisms; Coxon, J. M. Ed.; JAI Press: Greenwich, CT, 1993.
2. Yokoo, M.; Ogura, J.; Kanzawa, T. Polym. Lett. 1967, 5, 57.
3. Otera, J.; Yano, T.; Okawara, R. CL 1985, 901. Otera, J.; Yano, T.; Okawara, R. OM 1986, 5, 1167.
4. (a) Otera, J.; Yano, T.; Kawabata, A.; Nozaki, H. TL 1986, 27, 2383. (b) Otera, J.; Ioka, S.; Nozaki, H. CC 1989, 54, 4013. (c) Otera, J.; Dan-oh, N.; Nozaki, H. JOC 1991, 56, 5307. (d) Otera, J.; Dan-oh, N.; Nozaki, H. CC 1991, 1742. (e) Otera, J.; Dan-oh, N.; Nozaki, H. T 1993, 49. (f) Otera, J. CRV 1993, 93, 1449.
5. Otera, J.; Yano, T.; Himeno, Y.; Nozaki, H. TL 1986, 27, 4501.
6. Otera, J.; Mizutani, T.; Nozaki, H. OM 1989, 8, 2063. Otera, J.; Dan-oh, N.; Nozaki, H. T 1992, 48, 1449.
7. Otera, J.; Nozaki, H. TL 1986, 27, 5743.

Junzo Otera

Okayama University of Science, Japan

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