Preparation tributyltin methoxide

This was prepared from the diol 20 (eluant chloroform), yields 77% (A) and 87% (B) as a syrup (film) 1740 (CO) and 3500 cm-1 (OH). When either molecular sieves or tributyltin methoxide were omitted, the yield dropped to 37% [27]. 

Yamamoto has recently described a novel catalytic, asymmetric aldol addition reaction of enol stannanes 19 and 21 with aldehydes (Eqs. 8B2.6 and 8B2.7) [14]. The stannyl ketones are prepared solvent-free by treatment of the corresponding enol acetates with tributyltin methoxide. Although, in general, these enolates are known to exist as mixtures of C- and 0-bound tautomers, it is reported that the mixture may be utilized in the catalytic process. The complexes Yamamoto utilized in this unprecedented process are noteworthy in their novelty as catalysts for catalytic C-C bond-forming reactions. The active complex is generated upon treatment of Ag(OTf) with (R)-BINAP in THF. Under optimal conditions, 10 mol % catalyst 20 effects the addition of enol stannanes with benzaldehyde, hydrocinnamaldehyde, or cinnamaldehyde to give the adducts of acetone, rerf-butyl methyl ketone (pinacolone), and acetophenone in good yields and 41-95% ee (Table 8B2.3). 

The tributyltin enolates 74 are readily prepared from the corresponding enol acetates and tributyltin methoxide in the absence of solvent [34]. The tin enolates thus obtained occur in the 0-Sn form and/or the C-Sn form, and both species can be used for the aldol reaction of this system. Although the tin enolates themselves have adequate reactivity toward aldehydes [34c], in the presence of the BINAP silver(I) catalyst the reaction proceeds much faster even at -20 °C. Optimum conditions entail the use of THF as solvent and the results employing these conditions in the catalytic enan-tioselective aldol reaction of a variety of tributyltin enolates with typical aromatic, a,/3-unsaturated, and aliphatic aldehydes are summarized in Table 2. TTie characteristic features are (i) All reactions proceed to furnish the corresponding aldol adducts 75 in moderate to high yield in the presence of 10 mol % (i )-BINAP AgOTf complex at -20 °C for 8 h, and no dehydrated aldol adduct is observed (ii) with an a,j3-unsaturated aldehyde, the 1,2-addition reaction takes place exclusively (entry 3) (iii) a bulky alkyl substituent of tin enolate increases the enantioselectivity of the aldol reaction. For instance, the highest ee (95 % ee) is obtained when the tin enolate prepared from pinacolone 77 or rert-butyl ethyl ketone 79 is added to aldehydes (entries 2, 7, and 8) (iv) addition of the cyclohexanone-derived enol tributylstannane 78 (( )-... 

Analogous carbonyl-forming eliminations occur with the adducts formed between organotin oxides or alkoxides and trihalogenomethyl aldehydes or ketones, and tributyl-trichloromethyltin was first prepared by the elimination of methyl trichloroacetate from the adduct of tributyltin methoxide and hexachloroacetone.135 136... 

A number of methods are now available for preparing the tin enolates, which are often not isolated, but are generated and caused to react further in situ. Tributyltin methoxide reacts exothermically with enol acetates without a solvent, to give the corresponding stannyl enolate, and methyl acetate which can be removed under reduced pressure or by slow distillation (b.p. 57 °C) (e.g. equation I4-54).37-104-105... 

Bis(tributyltin) enediolates can be prepared from the reaction of acyloins with bis(tributyltin) oxide or tributyltin methoxide (equation 14-61).112... 

The reaction of less electrophilic halides, particularly aryl and vinyl halides, can be catalysed with a palladium compound (equations 14-63 and 14-64),115 and the tin enolate can be prepared in situ from the enol acetate and tributyltin methoxide, or lithium enolate and tributyltin trifluoroacetate, or silyl enolate and tributyltin fluoride. 

Whereas alkoxystannanes can be prepared by azeotropic dehydration of a mixture of bis(tributyltin) oxide and an alcohol (pKa ca. 16), aminotin compounds cannot normally be prepared from the oxide and an amine (pKa ca. 35). The important exception to this rule is pyrrole which is a stronger acid (pKa 15), and iV-tributylstannylpyrrole can readily be prepared by the azeotropic dehydration of bis(tributyltin) oxide and pyrrole, or by heating together tributyltin methoxide and pyrrole.3... 

Not only silyl end ethers but also enol acetates prepared from saturated ketones give a,/3-unsaturated ketones by heating with allyl methyl carbonate in the presence of Pd(II)(OAc)2 and dppe with tributyltin methoxide as a bimetallic catalyst (Scheme 12). Regioselective generation of palladium(II) enolate intermediate is simply carried out by treatment of allyl enol carbonates, which are prepared by trapping of ketone enolates with chloroformate, with Pd(II)(OAc)2 in the presence of dppe (Scheme 13). 7r-Allylpal-ladium(II) enolates thus generated provide a,/3-nnsatnrated ketones. 

The use of tributyltin methoxide seems to be specific to reactions of isopropenyl acetate, giving a method for the a-arylation of acetone. Aryl-acetones have also been prepared by the copper-catalysed arylation of acetylacetone in di-methylformamide at elevated temperatures. p-Keto-esters may also be arylated with the aryl-lead reagents that are prepared in situ from diarylmercury compounds and lead tetra-acetate. ... 

Reversibility of the insertion of CO2 provides a convenient route to some metal alkoxides by a process generalized earlier [reaction (g), 11.5.1]. For example, tributyl-tin(IV) methoxide can be prepared by treating tributyltin(IV) chloride with sodium methoxide, but it can be difficult to separate the finely divided sodium chloride that is formed. It is easier to heat bis(tributyltin) oxide with methyl carbonate tributyltin(lV) methoxide and methyl tributyltin carbonate are first formed in an exchange reaction ... 

Fluoromethylenation.11 Methods for fluoromethylcnation of ketones result in mixtures of (K)- and (Z)-vinyl fluorides, which are difficult to separate. A selective route involves reaction of the ketone with the carbanion of l-fluoro-l-(phenylsulfonyl)methane-phosphonate, prepared from fluoromethyl phenyl sulfones and diethyl chlorophosphate. The reaction provides mixtures of (E)- and (Z)-fluorovinyl sulfones, which can be separated by flash chromatography. Those products cannot be reduced by AI(Hg), but on treatment with tributyltin hydride (A1BN), they are converted into (fluorovinyl)stannancs with retention. Dcstannylation to vinyl fluorides can be effected with sodium methoxide in methanol or with CsF in methanolic ammonia.14... 

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