Tributyltin ethers

Selective oxidation of sec -alcohols.1 The final steps in a synthesis of spec-tinomycin (3), an aminocyclitol antibiotic, involved a selective oxidation of one of three alcohol groups of 1 to provide 2, which furnishes 3 on deprotection (H2/Pd/ C, 90% yield). This oxidation can be carried out by conversion to a tributyltin ether followed by NBS oxidation to an a-hydroxy ketone in 80% yield (crude). Alternatively, reaction with Bu2SnO provides a stannylidene acetal, which is also oxidized by NBS to 2 in high yield. 

Activation of 26 with AgBF, led to the intermediate 1,2-A-sulfonylaziridinc, which reacted with the tributyltin ether glycal 27 to afford the dimer 28. The second glycal was activated with dimethyldioxirane (DMDO) to supply the intermediate epoxide that was treated with ZnCl2 and allyl alcohol to afford compound 29. 

Typical n9Sn NMR Chemical Shifts of Tributyltin Ethers ... 

Tin-carbon coupling constants can be useful in making assigments for tributyltin ethers. Values for 2/c,sn lie between 22 and 32 Hz if the carbons are secondary,35 36 but are larger for primary carbons (46 Hz for one example35). The 3/c,sn values are of similar magnitude, ranging35,36 from 10... 

When a polyol is reacted with bis(tributyltin) oxide, all tributylstannyl ethers are formed and these interconvert readily at the reaction temperatures.35-36 Ogawa and Matsui suggested that oxygen atoms of tributyltin ethers that have adjacent oxygen atoms in appropriate orientations to coordinate with the tin atom are activated toward electrophiles74,75 specifically, equatorial oxygen atoms that have an adjacent axial oxygen atom,... 

Reactions of Dibutylstannylene Acetals and Tributyltin Ethers of tram- 1,2-Diols... 

When reactions are performed on tributylstannyl ethers and dibutylstan-nylene acetals of hexopyranoside derivatives that have more oxygen atoms, including the primary one, unprotected, markedly different results are obtained, as shown in Figs. 24 and 25. Dibutylstannylene acetals favor reaction on the position in the 1,2-diol unit that is adjacent to an axial substituent, whereas tributyltin ethers prefer to react at the primary centers. However, this pattern was not observed for reactions of the tributylstannyl ether of l,2-(l-methoxyethylidene)-j3-D-mannopyranose, as shown in Fig. 26.122 Methylation of this compound through the tributylstannyl ether in toluene in the presence of added tetrabutylammonium bromide also gave substitution on 0-3 predominantly.123 These results may arise from distortion of the chair conformation by the fused isopropylidene acetal. 

When the tributylstannyl ether of benzyl 3, 4 -0-isopropylidene-/3-lactoside (41) in toluene containing V-methylimidazole was treated with benzyl bromide, a mixture was obtained in which the 2-benzyl ether was the major product, isolated in 52% yield.142 A study of the alkylation of the tributyltin ether of benzyl jS-D-glucopyranoside has never been reported,... 

A very selective method of oxidizing secondary alcohols is bromino-lysis of tributyltin ethers prepared by the treatment of hydroxy compounds with bis(tributyl)tin oxide. The reaction is regio- and stereospecific and is an important means of oxidizing unprotected glycosides [734]. 

Trialkyltin alkoxides (86) and dialkylstannylene (87) have recently attracted attention because a tin atom attached to an oxygen atom enhances the nucleophilicity of the latter without increasing its basicity. The synthetic applications of tin alkoxides manifest most remarkably in the case of polyols. For example, 1,2,6-hexanetriol was first stannylated with 1 equiv. of (Bu3Sn)20, followed by treatment with benzoyl chloride giving (88) in 67% yield. Intermediacy of the tributyltin ether (89) was proposed for the regioselective benzoylation (Scheme 35). ... 

Two types of tin derivatives have been used mainly to achieve these reactions dialkylstannylene acetals are formed by reaction of dialkyltin oxides with diols tributyltin ethers are formed by reaction of bis(tributyltin) oxide with alcohols. Some aspects of the regioselectivity achieved with these two types of intermediates are the same, while others are different, as will be outlined in the sections to follow. Where the reaction outcomes are similar, the dialkyltin reagents are strongly preferred because of their lower toxicity. As these reagents are heavily employed, the topic has been reviewed several times, but siguilicant uew observatious continue to be made. This chapter is not intended to be a comprehensive summary of all applicatious of these intermediates, but will highlight examples of each type of selectivity. 

The first reactions using both dibutylstannylene acetals and tributyltin ethers as intermediates were performed in 1974 by Wagner et al., who formed benzoates and p-toluenesulfonates from dibutylstannylene acetals of nucleosides with good, but often opposite, regioselectivity and also formed phosphates from bis(tributyltin) ethers (Scheme 5.1.1). Shortly afterwards, David reacted dibutylstannylene acetals of diols with bromine to give mono-keto products highly selectively. ... 

A particular mole ratio of bis(tributyltin)oxide was reportedly required to regioselectively effect the tributyltin ether mediated 2-O-alkylation of methyl 4,6-O-benzylidene-a-D-glucopyranoside Dibutyltin oxide mediated alkylation of the same compound (BnBr, DMF) afforded predominantly the 2-0-benzyl ether in contrast to previous claims (c.f. Vol 27, Ch 5, ref. 15). 

---