Stannyls boron halides

Borylated alkynes that are stabilized through Lewis base coordination or r-donation from electron-donating amino and alkoxy substituents on boron are well studied. Their synthesis typically involves either the reaction of a bis(dialkylamino)haloborane with an acetylide to form a diaminoborylacetylene (equation 31), or the treatment of stannylated alkynes with boron halides. However, while alkynylboranes are readily available, in the absence of steric protection or electronic stabilization they tend to decompose thermally. 

Metalated ferrocenes also serve as convenient precursors to ferrocenylboranes. Lithiated ferrocenes have been ntilized for the preparation of ferrocenylboronates FcB(OR)2 and l,T-fc(B(OR)2)2 and are especially suitable in the presence of ort/ o-directing donor-substituents. The borylation of disilylated ferrocenes with excess BCI3 on the other hand was reported to yield varying amounts of 1,3-diborylated prodnct (82 M = Fe, X = Cl) in addition to the l,F-diborylated species (83 M = Fe, X = Cl). In contrast, when 1,F-distannylated ferrocenes were treated with equimolar amounts of boron halides, l-stannyl-2-borylferrocenes (86) were formed as the major product rather than the expected... 

Alkyl stannyl selenides are also useful nucleophilic selenium reagents. Tri-methylstannyl or tributylstannyl methyl selenides 58 react with halides 59 to produce unsymmetrical selenides 60 in good yields in the presence of a fluoride ion or by treatment with n-butyllithium (Scheme 44) [84]. Tributylstannyl phenyl selenide (61) reacts smoothly with acetals to give monoselenoacetals 62 in the presence of boron trifluoride etherate (Scheme 45 a) [85]. Similar reaction conditions were applied to the regioselective ring opening of epoxides (Scheme 45b) [86]. 

A different technique for the stannylation of an alkyne is shown in Scheme 8-1. Electrophiles add to the triple bond of lithium trialkylalkynylborates with migration of one of the alkyl groups to give a vinyl derivative, and when the electrophile is a trial-kyltin halide, the migrating group and the tin are situated trans.61 The ds-bimetallic alkene can then be demetallated providing a route to Z-alkenes, ketones, and alkynes. 9-BBN Can be used as the source of the boron to conserve a valuable alkyl group.62... 

Cleavage of the boron—Co bond by tin halides yields Sn—boron bonds . The route supplements those involving stannyl-alkali-metal reagents and haloaminoboranes ( 5.3.17.2.2). 

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