Halides trialkyltin

Enantiomerically enriched l-(diisopropylaminocarbonyloxy)allyllithium derivatives (Section 1.3.3.3.1.2.) add to carbonyl compounds with syn-l,3-chirality transfer21, giving good evidence for a pericyclic transition state in the main reaction path (Section 1.3.3.1.). However, since the simple diastereoselectivity and the degree of chirality transfer are low, for synthetic purposes a metal exchange with titanium reagents or trialkyltin halides (Section D.1.3.3.3.8.2.3.) is recommended. 

A cyclic mechanism has been tentatively proposed for the reaction involving trialkyltin halides. 

A trialkyl- or triarylstannyl group can also be added to an aromatic ring. One way this can be accomplished is by treating an aromatic or heteroaromatic compound possessing an active hydrogen(s) with an alkyl lithium and then reacting the lithium salt with a trialkyltin halide (equation 97). Another general method that has been used to attach a trialkyl- or... 

The reduction of trialkyltin halides by PMHS is catalyzed by aqueous KF and can be used in situ for free radical- or palladium-catalyzed reactions of the stannanes, and this protocol probably provides the best way of... 

Hexabutyldistannane, which is an important reagent in many organic syntheses, can be prepared very conveniently by reducing bis(tributyltin) oxide with sodium borohydride in ethanol at room temperature. After 5 min, the only tin species present is tributyltin hydride, but in 2 h, its decomposition is catalyzed by the ethoxide ion that is formed to give the distannane in 83% yield.444 Hexaalkyldistannanes, R3SnSnR3 (R = Et, Pr, or Bu), are obtained in ca. 50% yield when the corresponding trialkyltin halides are treated with zinc powder in THF.445... 

These observations do not, however, mean that TBT carboxylates and TBTCl are ionic in nature. After detailed analysis of the physical evidence such as the low specific conductance and dipole moment of trialkyltin halides, Neumann has concluded that they have no "salt-like constitution" (6). Bonding in the trialkyltin carboxylates also is essentially similar to that in covalent alkyl esters, as evidenced by the low dipole moment of 2.2D for tributyltin acetate in benzene, as compared to 1.9D for alkyl acetates (7). 

Results of a chemical activation induced by ultrasound have been reported by Nakamura et al. in the initiation of radical chain reactions with tin radicals [59]. When an aerated solution of R3SnH and an olefin is sonicated at low temperatures (0 to 10 °C), hydroxystannation of the double bond occurs and not the conventional hydrostannation achieved under silent conditions (Scheme 3.10). This point evidences the differences between radical sonochemistry and the classical free radical chemistry. The result was interpreted on the basis of the generation of tin and peroxy radicals in the region of hot cavities, which then undergo synthetic reactions in the bulk liquid phase. These findings also enable the sonochemical synthesis of alkyl hydroperoxides by aerobic reductive oxygenation of alkyl halides [60], and the aerobic catalytic conversion of alkyl halides into alcohols by trialkyltin halides [61]. 

Not only trialkyltin halides, but also tetraalkyltins themselves act in this way as perturbers . Evidence for this effect was obtained47 by determination of the relative reactivities of alkyl groups in unsymmetrical tetraalkyltins. The following data are typical. 

Pyridylstannanes are accessed by transmetallation of pyridyllithium reagents with trialkyltin halides such as tributyltin chloride <20000L3373, 1998JA2805> and typically utilized as coupling partners in Stille reactions with... 

The reaction of the cluster [Ni (CO)i2]-2 with trialkyltin halides form [Ni(SnRCl2)4 (CO)]-2 (R = Me, Bu), which are precursors of polynuclear [Nin(SnR)2(CO)i8]-2, based upon a Ni-centered NiioSn2 icosahedral cage231. 

Most benzylic organolithiums, unless they bear an a heteroatom, are configurationally unstable over a period of seconds or more (see section 5.1.11), so any stereoselectivity in lateral lithiation is rarely detectable. However, as implied above, the lateral lithiation of tertiary 1-naphthamides 344 is stereoselective, and yields a single diastereoisomeric atropisomer of the organolithium 346b.159-139-140 Both diastereoisomers of 346 were characterised by NMR. These organolithiums react with most electrophiles to give 372 with retention of stereochemistry, but with trialkyltin halides with inversion (see section 6.1.4). 

Tin(iv) enolates are normally generated by transmetallation from lithium enolates with trialkyltin halides or transesterification between enol acetates with trialkyltin alkoxides.220 Other types of generation systems are described below. 

Pentaalkylditin lithium, RjSujLi (R = Me, n-Pr, i-Pr) is present in preparations of RjSnLi reagents prepared from the trialkyltin halide and Li metal in THF. The RjSnjLi species arise by oxidative addition of RjSnLi to the stannylene R2Sn which in turn is a significant component of the equilibrium ... 

The trifluoromethyltin halides, (CF3) SnX4 react with trimethyl- or tributyl-tin hydride at -40 °C to give the trialkyltin halide and the corresponding trifluoromethyltin hydrides (CF3)3SnH, (CF3)2SnH2, CF3SnH3, and (CF3)2SnClH as liquids which are unstable at room temperature.18... 

The resin-bound trialkyltin halide developed for this reaction required higher catalytic loadings (30-100%) to obtain reasonable yields of coupled product, (Scheme 5.8.12), presumably reflecting the availability of the catalytic site in the biphasic mixture. Tin contamination of the column purified product, however, was <5-60 ppm compared with >500 ppm obtained for the free trimethyltin chloride-catalyzed reaction. 

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