Di-n-butyltin Oxide1,2

Bu2SnO

[818-08-6]  · C8H18OSn  · Di-n-butyltin Oxide  · (MW 248.92)

(converts diols to O-stannylene acetals2 which undergo regioselective acylation, alkylation, oxidation, and condensation with activated carboxylic acid derivatives; activates a,o-hydroxy acids and a,o-amino acids for lactone and lactam formation, respectively;3 mediates epoxidation of allylic alcohols by t-butyl hydroperoxide;4 catalyzes TMSN3 addition to nitrile;5 useful as a source of tin for Otera transesterification6 and organotin phosphate condensate7 catalysts)

Alternate Name: DBTO.

Physical Data: mp >300 °C.

Solubility: insol most organic solvents with which it does not react. However solvents like toluene, benzene, and methanol are routinely used for reactions of hydroxylic substrates.

Form Supplied in: white powder.

Handling, Storage, and Precautions: toxic and irritant;8,9 use in a fume hood.

Introduction.

Di-n-butyltin oxide, because of its biocidal and antifouling properties, is one of the most widely used industrial chemicals.9 It is the final product of hydrolysis of dialkyltin halides (eq 1) and exists as an amorphous polymeric solid insoluble in nonreacting solvents. A reticulated network (1) consisting of four-membered rings of alternating tin and oxygen has been suggested as a possible structure for this compound.10 The interaction of diorganotin oxides with various biomolecules like amino acids, peptides, carbohydrates, and nucleic acid components has been reviewed9 and is beyond the scope of this article.

Formation and Reactions of Dibutylstannylenes.

By far the largest application of DBTO in organic chemistry is in the generation and reactions of stannylenes from polyhydroxy compounds. Dibutylstannylenes are prepared in nearly quantitative yields by heating stoichiometric amounts of DBTO and the polyol in a solvent such as benzene or toluene with concomitant removal of water (eq 2).11 Compounds (2)12 and (3)13 are other prototypical stannylenes that have been prepared by this method. Formation and reactions of 1,6-stannylenes from monosaccharides have also been reported recently.14 While the stannylene from ethylene glycol (eq 2) is an infinite coordination chain polymer with hexacoordinated Sn,15 the stannylenes from cyclohexane-1,2-diols and the methyl 4,6-O-benzylidene-a-D-glucopyranoside (3)16 are dimeric (e.g. 4).

Regioselective Alkylation, Acylation, and Sulfonylation.

Synthetic applications of stannylenes have followed the elegant studies of Moffatt17 and Ogawa,18 who showed that the inherent differences in the nucleophilicities of carbohydrate hydroxys can be amplified by the formation of trialkyltin ethers. Several selective acylations and alkylations could thus be accomplished. Further it was noted that while acylation proceeds without any catalyst, alkylation is a sluggish reaction and needs assistance from tetrabutylammonium halides (eq 3).19

Reactions of stannylene (2) are typical and are shown in eq 4.2

The stannylene (3) reacts with benzoyl chloride or tosyl chloride to give the corresponding 2-O-derivative (eq 5). The alkylation is less selective.20 Use of nonpolar solvents and tetrabutylammonium halide has been a significant improvement (eq 6) in this alkylation procedure.21 Several other examples of selective acylation and alkylations are given by David and Hanessian.2 An intramolecular ether formation using DBTO has been used for the synthesis of octosyl acid.22 Monoacylation of dimethyl L-tartrate has been carried out using this procedure (eq 7).23 Two highly readable accounts of how the anomer composition and stoichiometry of reagents affect the regiochemistry of acylation24 and tosylation25 have recently appeared.

The structure of the dimeric complex (4) has been used to explain the observed preferential reactivity of the C-2 hydroxy groups.2 It is argued that the divalent oxygens that occupy the axial position within the tin cordination sphere (i.e. this case, the C-2 oxygens) are not only more nucleophilic, but also are more accessible sterically. It is believed that the orientational preference of the hydroxy group is related to its acidity, and thus by forming a Sn complex with the more acidic hydroxy group in the axial position, its reactivity towards nucleophiles is enhanced. The stannylene procedure can be used to reverse the stereochemistry of the classical monoacylation regiochemistry observed in some unsymmetrical diols.26

Regioselective Oxidation.

Following the original discovery by David and Thieffrey,27 several stannylenes have been oxidized by bromine to acyloins (eq 8). Hanessian employed this reaction for the synthesis of a densely functionalized intermediate which was converted into (+)-spectinomycin.28 A detailed study of monooxidation of unprotected carbohydrates has also appeared.29 Stannylenes are oxidized the same way as diols, with Sodium Periodate and Lead(IV) Acetate.2

Esterification Catalyst.

In the presence of DBTO, alcohols react with carboxylic acids to give esters30 and the reaction can be extended to make lactones and lactams (eqs 9 and 10).3 It should be noted that the stereochemistry of the alcohol center is unaffected. A template-driven extrusion process, in which an intermediate where the hydroxy and the carboxyl groups are brought into close proximity by tin oxide, has been proposed for this reaction.

Stannylenes derived from diols react with bifunctional carboxylic acid derivatives to give macrocyclic polyolides of various sizes.31,32 This approach has been used for the synthesis of (+)-dicrotaline (eq 11).33

Dibutyltin oxide is the best source of tin for the Otera transesterification catalysts (eq 12),6 which have found wide use in organic synthesis. DBTO has also been used as a catalyst for hydrolysis of amides in very sensitive molecules, where other procedures have failed.34

Catalyst in Oxidation Reactions.

DBTO has been used as a catalyst in FeIII-mediated oxidation of thiols to disulfides, even though Tri-n-butyl(methoxy)stannane seems to be better suited for this purpose.35 Epoxidation of terminal alkenes in a two-phase system (chloroform-water) containing H2O2/ammonium molybdate/DBTO has also been reported.36 A combination of DBTO and t-Butyl Hydroperoxide oxidizes allylic alcohols with moderate regio- and stereoselectivity.4 Tri- and tetrasubstituted double bonds are most easily oxidized and the selectivities are comparable to those of the corresponding Vanadyl Bis(acetylacetonate) mediated reactions.

Miscelleneous Applications.

The method of choice for the regioselective opening of benzylic and tertiary epoxides with alcohols (eq 13) appears to be a reaction mediated by organotin phosphate condensate (OPC), which is readily prepared from DBTO and tributyl phosphate.7 DBTO catalyzes rearrangement of 3-hydroxy-2-oxo carboxylic acid esters (eq 14), a reaction reminiscent of a similar one mediated by the enzyme reductoisomerase.37 DBTO has been used as a catalyst for the addition of Azidotrimethylsilane to nitriles5 for the production of tetrazoles (eq 15).


1. Pereyre, M.; Quintard, J. P.; Rahm, A. Tin in Organic Synthesis; Butterworth: London, 1987.
2. David, S.; Hanessian, S. T 1985, 41, 643.
3. Steliou, K.; Poupart, M. A. JACS 1983, 105, 7130. See also: Steliou, K.; Szczygielska-Nowosielska, A.; Favre, A.; Poupart, M. A.; Hanessian, S. JACS 1980, 102, 7578.
4. Kanemoto, S.; Nonaka, T.; Oshima, K.; Utimoto, K.; Nozaki, H. TL 1986, 27, 3387. For the possible structure of the reagent see: Davies, A. G.; Grahan, I. F. CI(L) 1963, 1622.
5. Wittenberger, S. J.; Donner, B. G. JOC 1993, 58, 4139.
6. Otera, J.; Dan-oh, N.; Nozaki, H. JOC 1991, 56, 5307.
7. Otera, J.; Niibo, Y.; Nozaki, H. T 1991, 47, 7625.
8. Selwyn, M. J. In Chemistry of Tin; Harrison, P. G., Ed.; Chapman and Hall: New York, 1989; p 359.
9. Molloy, K. C. In The Chemistry of the Metal-Carbon Bond; Hartley, F. R., Ed.; Wiley: Chichester, 1989; Vol. 5, p 465.
10. Davies, A. J.; Smith, P. J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 2, p 519.
11. Considine, W. J. JOM 1966, 5, 263. This compound was first described in the patent literature: Ramsden, H. E.; Banks, C. K. U.S. Patent 2 789 994, 1957.
12. Wagner, D.; Verheyden, J. P. H.; Moffatt, J. G. JOC 1974, 39, 24.
13. David, S.; Thieffry, A. CR(C) 1974, 279, 1045.
14. Köpper, S.; Brandenburg, A. LA 1992, 933.
15. Davies, A. G.; Price, A. J.; Dawes, H. M.; Hursthouse, M. B. JCS(D) 1986, 297. See also Ref. 10.
16. David, S.; Pascard, C.; Cesario, M. NJC 1979, 3, 63.
17. Jenkins, I. D.; Verheyden, J. P. H.; Moffatt, J. G. JACS 1971, 93, 4323.
18. Ogawa, T.; Matsui, M. Carbohydr. Res. 1977, 56, C1. See also: Ogawa, T.; Matsui, M. T 1981, 37, 2363.
19. Veyrières, A. JCS(P1) 1981, 1626. See also: David, S.; Thieffry, A.; Veyrières, A. JCS(P1) 1981, 1796.
20. Ogawa, T.; Kaburagi, T. Carbohydr. Res. 1982, 53, 1033. See also: Nashed, M. A.; Anderson, L. TL 1976, 3503. For a recent reference dealing with related chemistry in partially protected carbohydrates see: Tsuda, Y.; Nishimura, M.; Kobayashi, T.; Sato, Y.; Kanemitzu, K. CPB 1991, 39, 2883.
21. David, S.; Thieffry, A.; Veyrières, A. JCS(P1) 1981, 1796.
22. Danishefsky, S. J.; Hungate, R.; Schulte, G. JACS 1988, 110, 7434.
23. Nagashima, N.; Ohno, M. CL 1987, 141. For an application in the inositol area see: Yu, K.-L.; Fraser-Reid, B. TL 1988, 29, 979.
24. Helm, R. F.; Ralph, J.; Anderson, L. JOC 1991, 56, 7015.
25. Tsuda, Y.; Nishimura, M.; Kobayashi, T.; Sato, Y.; Kanemitzu, K. CPB 1991, 39, 2883.
26. Ricci, A.; Roelens, S.; Vannuchi, A. CC 1985, 1457.
27. David, S.; Thieffry, A. JCS(P1) 1979, 1568. For such oxidations on unprotected carbohydrates see: Tsuda, Y.; Hanajima, M.; Matsuhira, N.; Okuno, Y.; Kanemitzu, K. CPB 1989, 37, 2344.
28. Hanessian, S.; Roy, R. JACS 1979, 101, 5839.
29. Tsuda, Y.; Hanajima, M.; Matsuhira, N.; Okuno, Y.; Kanemitzu, K. CPB 1989, 37, 2344.
30. Habib, O. M. O.; Malek, J. CCC 1976, 41, 2724.
31. Shanzer, A. ACR 1983, 16, 60.
32. Bredenkamp, M. W.; Flowers, H. M.; Holzapfel, C. W. CB 1992, 125, 1159.
33. Niwa, H.; Okamoto, O.; Ishiwata, H.; Kuroda, A.; Uosaki, Y.; Yamada, K. BCJ 1988, 61, 3017.
34. Chwang, T. L.; Nemec, J.; Welch, A. D. J. Carbohydr., Nucleosides Nucleotides 1980, 7, 159.
35. Tsuneo, S.; Otera, J.; Nozaki, H. TL 1990, 31, 3591.
36. Kamiyama, T.; Inoue, M.; Kashiwagi, H.; Enomoto, S. BCJ 1990, 63, 1559. and references cited therein.
37. Crout, D. H. G.; Rathone, D. L. CC 1987, 290.

T. V. (Babu) RajanBabu

The Ohio State University, Columbus, OH, USA



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