Tributyltin triflate

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

Hydrostannation of carbonyl compounds with tributyltin hydride is promoted by radical initiation and Lewis or protic acid catalysis.The activation of the carbonyl group by the acidic species allows the weakly nucleophilic tin hydride to react via a polar mechanism. Silica gel was a suitable catalyst allowing chemoselective reduction of carbonyl groups under conditions that left many functional groups unchanged. Tributyltin triflate generated in situ from the tin hydride and triflic acid was a particularly efficient catalyst for the reduction of aldehydes and ketones with tributyltin hydride in benzene or 1,2-di-chloromethane at room temperature. Esters and ketals were not affected under these conditions and certain aldehydes were reduced selectively in preference to ketones. 

The transformation has been extended even further to p)ran derivatives by using a tungsten pentacarbonyl-tetrahydrofuran complex. Primary, secondary, and tertiary l-alkyn-5-ols 136 undergo cyclization to dihydropyranylidene carbenes, which can then be converted into the corresponding stannyl dihydrop)Tanes 138 upon treatment with tributyltin triflate and triethy-lamine (O Scheme 46) [236],... 

The hydrostannation of aliphatic and aromatic aldehydes and ketones is catalysed by tributyltin triflate, Bu3Sn0S02CF3, acting as a Lewis acid, and this can be formed in situ from the reaction between triflic acid and tributyltin hydride.72... 

Tributyltin triflate (a) Evans, D.A., Trotter, B.W., C6te, B. Tetrahedron Lett. 

A range of aliphatic aldehydes have been converted to the corresponding chiral P-lactones by the reaction with ketene in the presence of the chiral oxazaborolidine and tributyltin triflate as catalysts with up to 84% ee. 

The authors proposed that the chiral BLA (5), generated by the reaction of the chiral oxazaborolidine (4) and tributyltin triflate, acts as a chiral Lewis acid catalyst in this system. Noteworthy is the fact that the absolute configuration of the p-lactone can be predicted by the transition state assembly in Scheme 1.8, which is analogous to that of well-known CBS reduction. 

The coupling between an aryl halide or triflate and an amine is known as the Buchwald-Hartwig amination [138]. Originally it was described using a tributyltin amine [139,140] and was thus considered to be a coupling reaction. Subsequently, tributyltin amine was replaced by a standard amine and a strong base. It is a reaction of great academic and industrial interest [11]. 

As depicted in Scheme 3-25, the aldol reaction carried out at —78°C can give the corresponding aldol adduct 72 in 78% yield with 82% ee. The combination of chiral diamine-coordinated tin(II) triflate and tributyltin fluoride is so essential that the enantioselectivity cannot be obtained without tributyltin flu-... 

Like most aryl halides, furyl halides and furyl triflates have been coupled with a variety of organostannanes including alkenyl, aryl, and heteroaryl stannanes in the presence of catalytic palladium. Carbamoylstannane 66 was prepared by treating lithiated piperidine with carbon monoxide and tributyltin chloride sequentially. The Stille reaction of 66 and 3-bromofuran then gave rise to amide 67 [61]. In another example, lithiation of 4,4-dimethyl-2-oxazoline followed by quenching with MesSnCl resulted in 2-(tributylstannyl)-4,4-dimethyl-2-oxazoline (68) in 70-80% yield [62], Subsequent Stille reaction of 68 with 3-bromofuran afforded 2-(3 -furyl)-4,4-dimethyl-2-oxazoline (69). 

Analogously, 5-tributylstannylimidazole 29 was easily obtained from the regioselective deprotonation of 1,2-disubstituted imidazole 28 at C(5) followed by treatment with tributyltin chloride [24]. In the presence of 2.6 equivalents of LiCl, the Stille reaction of 29 with aryl triflate 30 afforded the desired 1,2,5-trisubstituted imidazole 31 with 2,6-di-tert-butyl-4-methylphenol (BHT) as a radical scavenger. Reversal of the nucleophile and electrophile of the Stille reaction also provided satisfactory results. For example, the coupling reaction of 5-bromoimidazole 33, derived from imidazole 32 via a regioselective bromination at C(5), and vinylstannane 34 produced adduct 35 [24],... 

S. Kobayashi, T. Busujima, S. Nagayama, Scandium Triflate-Catalyzed Strecker-Type Readions of Aldehydes, Amines, and Tributyltin Cyanide in Both Organic and Aqueous Solutions. Achievement of Com-plde Recovery of the Tin Compounds toward Environmentally Friendly Chemical Processes Chem. Commun 1998, 981-982. 

An analogous mechanism was proposed for the conversion of the triflate 416 to the vinyl-, allyl- and allenyl-A2-cephems 448 in yields of 47-71% by the respective tributyltin compounds in the presence of cuprous chloride (Scheme 6.91) [176]. Accordingly, the cyclic allene 417 should be liberated from 416 in the first step. Then, the organocopper species would transfer a hydrocarbon group to the central allene carbon atom of 417, leading to an allyl anion derivative, which is protonated during the workup. These reactions of 416 and 443 indicate that the cyclic allenes 417 and 444 behave toward nucleophiles as 1,2-cyclohexadiene (6) (Schemes 6.11— 13) and its non-polar derivatives such as 215 (Scheme 6.51), 221 (Scheme 6.52), 311 (Scheme 6.67) and 333 (Schemes 6.71 and 6.73), that is, they interact with nucleophiles at the central carbon atom of the allene system exclusively. 

Although in the recent years the stereochemical control of aldol condensations has reached a level of efficiency which allows enantioselective syntheses of very complex compounds containing many asymmetric centres, the situation is still far from what one would consider "ideal". In the first place, the requirement of a substituent at the a-position of the enolate in order to achieve good stereoselection is a limitation which, however, can be overcome by using temporary bulky groups (such as alkylthio ethers, for instance). On the other hand, the ( )-enolates, which are necessary for the preparation of 2,3-anti aldols, are not so easily prepared as the (Z)-enolates and furthermore, they do not show selectivities as good as in the case of the (Z)-enolates. Finally, although elements other than boron -such as zirconium [30] and titanium [31]- have been also used succesfully much work remains to be done in the area of catalysis. In this context, the work of Mukaiyama and Kobayashi [32a,b,c] on asymmetric aldol reactions of silyl enol ethers with aldehydes promoted by tributyltin fluoride and a chiral diamine coordinated to tin(II) triflate... 

Table 9.6 shows the effect of both the addition time and the polarity of the solvent, as well as the nature of the aldehyde, in the catalytic asymmetric aldol condensation promoted by tributyltin fluoride and a chiral diamine coordinated to tin(n) triflate. 

A clean, Strecker-type synthesis of a-aminonitriles has been developed amine, aldehyde, tributyltin cyanide, and scandium(III) triflate (as catalyst) are mixed together at room temperature. Yields for a range of aliphatic and aromatic aldehydes are typically ca 90%, the solvent can be organic or aqueous, the 10% catalyst loading is recoverable and reusable, and the tin reagent is similarly recyclable. 

The cyclopropane is inert to tributyltin chloride, but reacts readily with more highly Lewis acidic tributyltin trifluoromethanesulfonate (triflate) [11]. The 3-stannyI ester 13 showed no sign of internal chelation Eq. (16). 

A similar electrophile, iodosyl triflate, CF3S020I0, was employed with arylsi-lanes [98]. The same reagent upon reaction with Me3SiCN formed (CN)2I+ TfO" which was coupled with tributyltin substituted arenes or heterocycles to afford bis(heteroaryl)iodonium triflates, e.g. dithienyl and difuryl derivatives [99]. However, this method gave poor results with nitrogen heterocycles. For them another approach was developed based on the reaction of the appropriate lithium compound with / -(dichloroiodo)chloroethylene (Scheme 33). Pyridine and quinoline compounds were formed in this way in moderate yield (23-71 %) [100]. 

Asymmetric aldol-type reactions.1 This chiral diamine (1) in combination with tin(II) triflate and tributyltin fluoride (15, 314-315) effects a highly enantioselective aldol-type reaction between ketene silyl acetals and aldehydes. A tentative structure (2) has been suggested for the promotor. 

Transfer of these reaction conditions to C-3-alkylated vinyl triflate 80 proved successful using both trimethylsilylethynyltributyltin and vinyl-tributyltin, giving coupled products 86 and 87 in 44 and 58% yields, respectively. It was found advantageous to raise the reaction temperature to 60 °C for these coupling reactions (Scheme 39). 

Initially, disappointing results were obtained on attempting to crosscouple to aryl stannanes. Phenyltributyltin, tetraphenyltin, (2-methoxyphenyl)tributyltin, and (4-methoxyphenyl)tributyltin gave no coupling under Farina s conditions with vinyl triflate 80. Pleasingly,... 

Trimethylsilyl cyanide (0.54 ml, 4 mmol) was added to a stirred suspension of iodosyl triflate (0.58 g, 2 mmol) in dichloromethane (15 ml) at — 78°C under nitrogen. The mixture was allowed to warm to — 20°C and stirred at this temperature for 15 min until the formation of a clear solution. The solution was cooled to — 78°C and transferred to a cold stirred solution of the appropriate tributyltin heterocycle (4 mmol) in dichloromethane (15 ml). The mixture was brought to room temperature and crystallized by the addition of dry hexane (20-30 ml). The precipitated iodonium salt was filtered under nitrogen, washed with dry ether (30 ml) and dried in vacuo. Mono or bis hetaryl iodonium salts prepared by these and related methods also involved groups coming from selenophene [23], pyrazoles [24], benzothiophene [21], etc. 

The diastereoselective aldol reaction of the tributyltin enolate of cyclohexanone with benzaldehyde in the presence of a catalytic amount of various metal triflates has been studied. The highest A-selectivity is observed with Pd(OTf)2, while Zn(OTf)2 in THF shows moderate yy -selectivity (Equation (68)).222 OSnBu3... 

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