Stannyllithiums

The reduction of the stannyl radical (t-Bu2MeSi)3Sn with alkali metals produces a variety of structural modifications depending on the solvent used (Scheme 2.55). Thus, in nonpolar heptane, a dimeric stannyllithium species [58c Li ]2 (E = Sn) was formed, whereas in more polar benzene, the monomeric pyramidal structure 58c [Ti -Li (C6H5)] was produced. In the latter compound the Li+ ion was covalently bonded to the anionic Sn atom being at the same time n -coordinated to the benzene ring. A similar monomeric pyramidal CIP 58c [Li (thf)2] was prepared by reduction in polar THE the addition of [2.2.2]cryptand to this compound resulted in the isolation of the free stannyl anion 58c K+([2.2.2]cryptand), in which the ion lacked its bonding to the Sn atom. ... 

Imidoylstannanes, R13SnCR2=NR3, can be prepared from the reaction of stannyllithium compounds with the corresponding imidoyl chlorides (C1CR2=NR3 R2 and R3 = aryl),163 or, more generally, from the reaction of an acylstannane with an amine.164 The imidoylstannane can then be reduced to an a-aminostannane (Equation (49)).165... 

Stannyllithium compounds are important as sources of nucleophilic stannyl anions, and the dialkyltin lithium hydrides, R2SnLiH, have recently come to prominence as their reaction with electrophilic alkyl halides gives hydrides, R1R2SnH, with mixed alkyl groups (see Section 3.14.18.1).397... 

Addition of tri-H -butyl stannyllithium to aldehydes, followed by iodination and dehydro-halogenation, gives primarily is-alkeny Istannancs.99 100 101 102... 

Equimolar amounts of lithium diisopropylamide (LDA) and tin hydrides reacted in THF to form diisopropylamine and the corresponding stannyllithium (equation 12)27,28. In diethyl ether or hexane, an excess of tin hydride was required for complete reaction which leads to the ditin compound and lithium hydride (equation 13). 

A series of aryl and alkylarylgermyllithiums and stannyllithiums were synthesized in the same way with the purpose of transforming them by laser photolysis into the corresponding metal-centered radicals33 (equation 20). 

The reaction of tri(substituted allyl) stannyllithium with (substituted allyl)lithium formed an equilibrium mixture of tri(substituted allyl) stannyllithiums having all possible combinations of substituents (equation 196)204. 

Stannyllithiums are synthetic equivalent of stannyl anions. The reaction of 2,6-di- 7 /-butyl-4-rncthylphcnyl(UI IT) esters with BuLi, followed by the addition of Bu3SnLi, and trapping of the resulting lithium enolate with phenyldi-methylchlorosilane leads to silyloxyvinylstannanes, which are allowed to the subsequent coupling with vinyl iodides (Equation (110)).279... 

Scheme 19-1 Reactions of stannyllithium compounds with electrophiles.

Stannylaluminium compounds have been prepared from the stannyllithium compounds (equation 19-18) and their cuprates have been used in the stannylmetallation of terminal alkyncs and enynes.21 59... 

Examples of these compounds are given in Table 19-4. The stannylzinc compounds have been used in the presence of a copper or platinum catalyst for preparing vinylstan-nanes from terminal alkynes or from vinyl triflates,20 83> 84 but these reagents seem to have little advantage over the more readily available stannyllithium or stannylmagne-sium compounds. 

Bromo-2-chloropyrimidine is stannylated in the 5-position (195) (Scheme 42). The reaction of 2,4-dibromopyrimidine with trimethylstan-nylsodium results in regioselective substitution in the 2-position to furnish 4-bromo-2-trimethylstannylpyrimidine (196), whereas reactions with the corresponding stannyllithium reagent failed (94T275). 

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