Butyltin halides

Sawyer AK, Brown YE, Hanson EL (1965) Di-n-butyltin halide hydrides. J Organomet Chem... 

Butyltin halides have also been used to mediate this process. One of the first examples involved addition of a 3 1 mixture of tram- and ds-crotyl tributyltin and a variety of conjugated aldehydes to Bu2SnCl2 without solvent to form (Z) homoallylic linear adducts (Table 22) [39], In this reaction, addition of the initially formed secondary allylic dibutylchlorostannane to the aldehydes must be faster than that of the tributyl crotylstannanes, and faster than 1,3-isomerization of the chlorostannane. Formation of the (Z) isomer is consistent with a chair transition state in which the allylic methyl group of the stannane adopts an axial orientation to avoid steric interactions with the adjacent stannane substituents (Eq. 23). 

Conversion of tri-n-butyltin halides to insoluble tri-n-butyltin fluoride at the end of the reaction has been proposed and in some cases, the presence of the fluoride anion in the reaction itself may simultaneously increase the reactivity of the organotin reagents.A recent improvement using liquid chromatography on a KF/silica gel mixture has also been shown to allow very clean and simple purification. ... 

Column temperatures of llO C for butyltin halides, 180 C for phenyltin halides, and 210°C for octyltin halides were found to be satisfactory. Small variations were made from these temperatures as the columns were progressively exhausted after continuous use. 

They concluded that it was not possible to analyse mixtures of the four n-butyltin-halides since tetra-n-butyltin consistently reacts with n-butyltin chloride to form tri-n-butyltinchloride. Mixtures of n butyltintrichloride, di-n-butyltintrichloride and tri-n-butyl-tinchloride can be successfully analysed in the liquid phase OE 4011 (Figure 126) or GI 7100FF. The analysis of mixtures of di-n-butyl-tindichloride, tri-n-butyltinchloride and tetra-n-butyltin is possible only on Carbowax 20M column (Figure 127). In Table 114 are shown results obtained on this column for a range of synthetic mixtures. 

The determination of the Concentrations in pyridine [N] which cause the coalescence of the signals of the diastereotopic groups of a 0.262 M solution methylneophyl-t-butyltin bromide (6) and of 0.332 M solution methylneophylphenyltin chloride (3) at 22 °C at respectively 60, 100 and 270 MHz shows12) that the k2 term is much smaller than the k3[N] term. From these results, it is clear that the inversion of the configuration of the metal atom of triorganotin halides is second-order in the nucleophile pyridine. An analogous rate equation has been found for the racemiza-tion of triorganosilicon halides 29), for which the activation entropy AS is about —50 e.u. Several mechanisms with increase of coordination number 30) can be proposed to account for this second order in the nucleophile 31) ... 

This material was used to show that tributyltin halides decompose into dibutyltin dihalides and butyltin trihalides in the environment. 

A third route to allenyltin halides involves transmetallation of isolable allenyltri-butyltin compounds, as exemplified by the reaction of allenyltributyltin with Bu2SnCl2 [68]. The resulting mixture of allenyl- and propargyldibutyltin chlorides reacts with various aldehydes to afford mixtures of propargyl- and allenylcarbinols (Eqs. 9.78 and 9.79). The yields of these additions are uniformly high, but the selectivity depends on the nature of the aldehyde substituent. The transmetallation route to allenyltin and -indium halides will be discussed in more detail in a later section. 

Tetrahydropyran can be prepared by heating 1,5-dihydroxypentane at 190-210 C in the presence of butyltin trichloride (Scheme 4.12a). When the reaction is carried out using a cobalt catalyst [prepared by heating cobalt(II) oxalate (ethanedioate) under hydrogen at 600 °C] instead of the tin halide, the product is 3,4-dihydro-2 -pyran (Scheme 4.12b). 

Cyclization of vinyl radicals. Vinyl radicals formed by reduction of vinyl halides with tri-n-butyltin hydride (AIBN, hv) can undergo intramolecular cyclization to a suitably situated double bond. When either a five- or a six-membered ring can be formed, the former ring is favoured. When cyclization could lead to a six- or seven-membered ring, only the former is formed, as in the cyclization of 1 to 2. The cyclization of 3 to 4 is particularly interesting because the exocyclic double bond is formed at a predictable and useful position, and because a quaternary centetis formed without difficulty. 

Polymer-supported di- -butylstannane (di-/i-butyltin hydride) (29) can also reduce alkyl halides and xanthates in solid phase (eq. 2.16). 

RX RCHO. Alkyl halides can be converted directly into aldehydes in moderate to high yield by reaction with carbon monoxide (1-3 atm.) and tri-n-butyltin hydride catalyzed by the palladium(O) complex. The reaction involves insertion of carbon monoxide to form an acyl halide, which is known to be reduced to an aldehyde under these conditions (10, 411). Direct reduction of the halide can be minimized by slow addition of the tin hydride to the reaction and by an increase in the carbon monoxide pressure. 

Fluorinated aUcyl vinyl and aryl cadmium reagents can be prepared in excellent yields just by stirring the fluorinated halides with activated cadmium metal. These reagents can then be used to prepare the corresponding fluorinated stan-nanes, which are versatile synthetic intermediate, by reacting them with tri-n-butyltin chloride at room temperature. Similar methods have been used to synthesize fluorinated copper reagents. ... 

Hydrogenolysis of the toluene-4-sulfonate of an alcohol may be carried out with a nucleophilic hydride such as lithium aluminium hydride. There are also a series of radical methods based on the reduction of alkyl halides with tri- -butyltin hydride (BUjSnH). Finally, the source of the hydrogen may be the electrophilic proton, exemplified by the decomposition of organometallic reagents such as the Grignard reagent with water. 

Reduedon of M dts under radical conditions, Reduclion of halides with tr -n butyltin hydride under radical conditions is considered to proceed by the following chain reaction ... 

W. P. Neumann, Synthesis, 1987, 665 discusses the reduction of acyl halides to aldehydes with tri-n-butyltin hydride. 

To decide between these two models, they compared rate-structure profiles for the disappearance of alkyl halides in contact with magnesium with rate-structure profiles for others models of reduction. These included (1) rate-structure profiles for the free radical reduction of alkyl chlorides with tri-M-butyltin hydride in diethyl ether [33], assuming... 

In a similar attempt to determine the nature of the rate-determining step in the reaction of aryl halides with magnesium, the kinetics of the reaction of substituted aryl bromides with magnesium and with tri-/i-butyltin hydride in ethereal solvents were examined [81c], using competitive kinetics techniques, and were correlated with the substituent effect using Hammett cr parameters. A Hammett plot log iK/K)=f(( x) then provided the value of the Hammett constant p for the reactions of aryl halides with magnesium and with tri-u-butyltin hydride in various solvents (Fig. 4 and Table 11). 

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