Hydrostannation unsaturated

In addition, Wu and Li recently have developed an efficient rhodium-catalyzed cascade hydrostannation/conjugate addition of terminal alkynes and unsaturated carbonyl compounds in water stereoselectively (Scheme 4.5).88... 

The Stille adduct of 2-bromothiophene and l-ethoxy-2-tributyl-n-stannylethene or 1-ethoxy-l-tri-n-butylstannylethene is a masked thienyl aldehyde or a masked ketone, respectively [77-80]. Vinylstannane 93, derived exclusively as the -isomer from hydrostannation of bis(trimethyl-silyl)propargyl amine (92), was coupled with 2-bromothiophene to form ( )-cinnamyl amine 94 upon acidic hydrolysis [81, 82], In another case, stereoisomerically pure phenyl ( )-2-tributylstannyl-2-alkenoate 95, arising from Pd-mediated hydrostannation of phenyl ( )-2-alkynoate, was joined with 2-iodothiophene to deliver the stereodefmed trisubstituted a,p-unsaturated ester 96 [83, 84],... 

The addition of metal-hydrogen bonds across carbon-carbon multiple bonds, called hydrometallations, are very important, versatile transformations in organic synthesis. First, they allow the synthesis of new organometallic compounds. The products thus formed may be further transformed into other valuable compounds. The two most important reactions, hydroboration and hydrosilylation, will be treated here in detail, whereas other hydrometallation reactions (hydroalanation, hydro-zirconation) will be discussed only briefly. Hydrostannation, a very important transformation of substituted unsaturated compounds, has no significance in the chemistry of hydrocarbons possessing nonactivated multiple bonds. 

Chemoselective reduction of the conjugated double bond of a, /f-unsaturated aldehydes such as citral (556) to give citronellal (577) is possible by Pd-catalysed hydrostannation in the presence of AcOH [213],... 

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

Copper(l) chloride in combination with tributyltin hydride shows unique character as an initiator of certain radical reactions. Hydrostannation of a,/3-unsaturated ketones with Bu3SnH is initiated by CuCl and the resulting tin enolates react with aldehydes under the influence of CuCl as a Lewis acid catalyst (Equation (81))/... 

Hydrostannation of highly polarized a,)8-unsaturated nitriles leads to the formation of N-stannylketenimines 31, 33) in what is considered to be a polar 1,4-addition. Thus, polar mechanisms are ascribed to reactions leading to either 1-cyanoalkyl or ketenimine adducts. 

Hydrostannation with tricyclohexyltin hydride is only successful with unactivated unsaturated compounds when the reaction is conducted at high temperature (110 °C) with azobis(isobutyronitrile) added portion-wise, as an initiator. Under these conditions, it gives the expected adducts 29, 32, 34, 36, 38, 40, 43, 45, 48, and 50 in good yields with total regiospecificity, the tin being linked to the terminal carbon atom of the unsaturated compound (Scheme 3.7.3). Hydrostannation of unactivated alkenes with tricyclohexyltin hydride has been reported up to now as being unsuccessful, even under high pressure. ... 

This access to a , y-bis(tricyclohexyltin)alkanes proves to be very convenient when the corresponding organic dihalides are available. When this is not the case, and when a , y-dienes are more easily accessible, a double hydrostannation of these unsaturated compounds can be used. As indicated above, this radical addition has to be conducted in less mild conditions than for the addition of tri-n-butyltin hydride, for instance, because of the bulkiness of the organotin center and also of the more nucleophilic character of the tricyclohexyltin radical. Nevertheless, the treatment of 4,4 -di(butenyl)biphenyl or 4,4 -bis(but-3-enyloxymethyl)biphenyl with tricyclohexyltin hydride at 130 °C over seven days affords the corresponding adducts 72 and 75 in good yields (Scheme 3.7.11). Due to its rapid decomposition at this temperature, the AIBN initiator has to be added in small portions for the duration of the reaction. 

General Reactivily. This reagent was recently introduced as an alternative to Bu2SnHCl having enhanced Lewis acidic character for hydrostannation of unsaturated alcohols. 

In hydrostannation, not only carbon-carbon unsaturated compounds but also compounds having C=0, C=N, N=N, N=C=S, N=C=0, etc. are used as the unsaturated compounds [1]. 

The fact that unsaturated halides have undergone reduction rather than hydrostannation could mean that reaction (30) is faster than reaction (27). Since carbon-halogen and tin-halogen bond energies can vary greatly, it would be expected that the rate of Eq. (30) can vary over a large range with the result that the addition reaction could be made to compete under appropriate circumstances (see Section D). 

Ketones with a,/3-unsaturation undergo reduction (see Section C) whereas nonconjugated unsaturated ketones undergo hydrostannation 49). Similar arguments could be invoked inthis case, but would be somewhat more speculative because little is known about the mechanism of carbonyl reduction... 

Among the other simple compounds reduced by diphenyltin dihydride are cyclohexanone (82%), benzaldehyde (62%), mesityl oxide (60%), and chalcone (75%). It can be seen that the yields are high with the simple ketones and aldehydes, and moderate in the case of the a,]8-unsaturated analogs. The cause of the lower yields has not been examined, but may be due to the occurrence of hydrostannation, particularly of the product alcohol, as a side reaction. In all of these cases the unsaturated alcohol was the reduction product the double bond was not reduced. The same is true when triphenyltin hydride is used in the reduction of methyl vinyl ketone and phenyl vinyl ketone 66). 

II Hydrostannation reaction of unsaturated nitriles with organotin hydrides RsSnH and R SnE ... 

The increase in activity in the field of organotin hydrides is mostly due to the facility of addition of the tin-hydrogen bond to unsaturated systems and to the multiple mechanistic investigations of the hydrostannation reaction. Hev is a number of organometallic reactions, i.e., addition to transition metal complexes7 condensation with metal alkyls yielding tin-metal derivatives and with metal amides for synthesis of compounds with longer tin chains. 

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