Organotin hydrides synthesis

H.G. Kuivii.a, Reduction of Organic Compounds by Organotin Hydrides, Synthesis 1970, 499. 

Unsymmetrical functional tetraorganotins are generally prepared by tin hydride addition (hydrostaimation) to functional unsaturated organic compounds (88) (see Hydroboration). The realization that organotin hydrides readily add to atiphatic carbon—carbon double and triple bonds forming tin—carbon bonds led to a synthetic method which does not rely on reactive organometatiic reagents for tin—carbon bond formation and, thus, allows the synthesis of... 

For reviews of organotin hydrides, see Neumann, W.R Synthesis, 1987,665 Kuivila, H.G. Synthesis, 1970,499, Acc. Chem. Res., 1968,1,299. Tributyltin hydride also reduces vinyl halides in the prescence of a palladium catalyst. See Uenishi, J. Kawahama, R. Shiga, Y Yonemitsu, O. Tsuji, J. Tetrahedron Lett., 1996, 37, 6759. 

The dehalogenation of organic halides by organotin hydrides takes place in most cases with a free-radical mechanism [1, 84, 85], The stereospecific reduction of 1,1-dibromo-l-alkenes with Bu3SnH discovered by Uenishi and coworkers [86-89], however, did not occur in the absence of palladium complexes and did not involve radicals. For the synthesis of (Z)-l-bromo-l-alkenes, [(PPh3)4Pd] proved to be the most effective catalyst which could also be generated in situ. The reaction in Eq. (7) proceeded at room temperature and a wide range of solvents could be used. 

U. Gerigk, M. Gerlach, W. P. Neumann, R. Vieler, and V. Weintritt, Polymer-supported organotin hydrides as immobilized reagents for free-radical synthesis. Synthesis, p. 448 (1990). 

M. Gerlach, F. Jordens, H. Kuhn, W. P. Neumann, and M. Peterseim, A polymer-supported organotin hydride and its multipurpose application in radical organic synthesis, J. Org. Chem. 56 5971 (1991). 

Another application of the direct alkylation of metal-14 anions is the synthesis of polymer-supported organotin hydrides. These were prepared by the reaction of stannyl group was separated from the phenyl ring of polystyrene by two, three or even four carbon spacers. These polymers were found to contain 0.8-1.4 mmol of Sn-H per gram. The reducing ability of the polymer-supported organotin hydrides was monitored by reactions with haloalkanes (Scheme 22)142. 

A number of organotin hydrides which carry a chiral group, usually menthyl or nor-bomyl, have been prepared for use in asymmetric synthesis.42 An example is shown in equation 15-19 the enantioselectivity in this reaction is enhanced by the presence of a Lewis acid (e.g. BF3 or Cp2ZrCl2), and ee values of up to about 80 have been achieved.43 Force field and MO methods have been used to model the transition state for hydrogen transfer in such reactions.44... 

In recent years, these reactions have found an important place in organic synthesis. We will consider in this chapter only the reactions of radicals with tin hydrides, and the basic hydrostannolysis processes that depend on these reactions. Hydrostannation reactions are covered in Section 4.4, and the reactions of stannyl radicals with substrates R X in Section 20.1.3. The further use of organotin hydrides in organic synthesis, which depends largely on transformations of the radicals R " in hydrostannolysis reactions, or of the radicals R3SnXY" in hydrostannation reactions, are beyond the scope of this book, but have been extensively reviewed.2 64 66 104 107... 

Reactions involving organotin hydrides, or allyltin compounds, or hexaalkyldistannanes as reactants, and stannyl radicals as intermediates, now hold an important place in organic synthesis, to the degree that this dominance of organotin reagents in mediating free radical reactions has been referred to as the tyranny of tin.4... 

Reduction of the halides with a metal hydride such as lithium aluminium hydride, sodium borohydride, or poly(methylhydrosiloxane) gives the corresponding organotin hydrides These have an important place in organic synthesis for the reduction of halides to hydrides (hydrostannolysis) and the addition to alkenes and alkynes (hydrostannation), by radical chain reactions. Further reactions may intervene between the pairs of reactions shown in Equations (1.1.3) and (1.1.4), and (1.1.4) and (1.1.5), and these reactions are particularly useful for inducing ring-closure reactions. 

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