Tin-lithium exchange reaction

The tin-lithium exchange reactions are thought to proceed with retention of stereochemistry. However, as the stannanes employed in this study were racemic, there is no evidence in support of this pathway. 

The tin-lithium exchange reaction does not play an important role for the generation of 1-halo-l-lithioalkenes. Whereas in a-bromoalkylstannanes tin-lithium exchange occurs upon treatment with n-butyllithium , the bromine rather than the tin is replaced against lithium, when a-bromovinylstannanes are allowed to react with w-butyllithium . 

The enantiomerically pure a-stannyl ether, (R)-l-benzyloxymethoxy-l-tributylstannyl-propane, can be obtained by resolution of the precursor compound. The tin - lithium exchange reaction, as well as the electrophilic substitution, occurred with retention of configuration to give (I )-2-(benzyloxymethoxy) butane only28. A later study examined more examples and also confirmed this result27. 

Both 1 and 2 are stereochemically stable and shelf stable -metalated ethers. Subsequent tin-lithium exchange reaction with bulyllithium occurs as expected with retention of configuration in both cases51. 

The classical tin-lithium exchange reaction was first applied to cyclopropanes in the stereospecific transformation of 7-ewrfo-bromo-7-ex o-trimethyltinnorcarane to the corresponding 7-exo-lithio compound with BuLi in THF, at -95 °C (vide supra)10. The retention of configuration in cyclopropyl tin-lithium exchange reactions has also been confirmed in monocyclic 2-metallacyclopropane carboxamides60. More recently, this metal exchange reaction was used for the preparation of sensitive methylenecyclopropanes (equation 21)61. 

Ketone dilithio a,ft-dianion species (74) have been generated by the tin-lithium exchange reaction of the lithium enolate of /3-tributyltin-substituted ketones.291 Reaction with carbon electrophiles gives substituted ketones. 

Ketone dilithio a,f - and a -dianions have been generated by a tin-lithium exchange reaction of the lithium enolate of /3-tributyltin-substituted ketones.30 A chelation-aided approach, which employs /S-dichlorobutyltin-substituted ketones and n-BuLi, has been used for the generation of ketone a, f) -dianions having the Z-geometry at the alkene. The generated dianions have been transformed into ketones... 

Reincorporation of the tin can be avoided by using a tri wry/stannane precursor.156 This means that the product organolithium can be trapped with other electrophiles, provided that the solvent is 10 1 hexane-ether, and not THF, which otherwise protonates the product organolithium.157 The hexane-ether mixture slows down the tin-lithium exchange reaction dramatically, and it proceeds only at room temperature. Cyclisation of 323 thus leads to the synthesis of a simple GABA uptake inhibitor 324. A-acyl pyrrolidines cannot be made directly from a-amido organolithiums, as these fail to cyclise, possibly because they are too well stabilised by O-Li coordination.138... 

Allylation of carbonyl and imino groups is one of the most convenient methods for the introduction of allylic functions.107-110 Allylic tin compounds have high interaction between C=C and C-Sn bonds which makes them more reactive than the corresponding silicon derivatives.111,112 In spite of their high reactivity, tin compounds are stable enough to be isolated and to react at ambient temperature under aerobic conditions. These factors allow them to be applicable to various types of reactions, for example, thermal,113 high-pressure,116 transition metal-catalyzed,117,118 radical,119,120 photochemical,121,122 tin-lithium exchange reactions,108,113 and so on. A broad... 

Goswami reported that a / -kctophosphonate ester, having a tributyltin substituent ft to a carbonyl, can serve as a precursor for the corresponding ketone a,/ -dianions (Scheme 8)9. The first deprotonation step was carried out by adding NaH, while the second involved a tin-lithium exchange reaction using n-BuLi. 

Diisopropyl 4-(trimethylsilyl)-2-oxobutylphosphonate is prepared by the regioselective silyla-tion of the 5 carbon of the P-ketophosphonate 1,4-dianion via a low-temperature tin-lithium exchange reaction (Scheme 2.11)." ... 

This, however, is not in agreement with the unsuccessful attempts by Seyferth and Vick to prepare 9 by tin-lithium exchange reactions using n-butyllithium. 

Although carried out with achiral or racemic substrates, a comprehensive study by Macdonald and McGarvey uncovered several important features of the tin-lithium exchange reaction [16]. The order of thermodynamic stabilities is [Eq.(7)j ... 

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