Stannyl ethers electrophilic substitution

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. 

Olefination of aldehydes with a-silyl- and a-stannyl-stabilized phosphonate carbanions derived from cyclo-[L-AP4-D-Val] allow a (Z)-selective access to a,p-substituted vinyl phosphonates (343) that have been transformed into enantiomerically pure 4-alkylidene 4PA derivatives (344) (Figure 54). " Electrophilic fluorination of lithiated bis-lactim ethers derived from cyclo-[L-AP4-D Val] (345) with commercial NFSi allow direct access to a-monofluor-inated phosphonate mimetics of naturally occurring phosphoserine (346) and phosphothreonine (347), in enantiomerically pure form and suitably protected for solid-phase peptide synthesis (Figure 55). ... 

With the stannyl group as electroauxiliary, oxonium or A-acyliminium ions can be generated, which react in an electrophilic intramolecular addition or aromatic substitution to afford cyclic six-membered ethers or amines or their benzo analogues [Table 7, numbers 20 and 21] [172b]. Swenton has explored the dependence of yield... 

The enhanced reactivity of the silyl- and stannyl-substituted alkenes is also favorable to the synthetic utility of carbocation-alkene reactions. Silyl enol ethers also show enhanced reactivity. Electrophilic attack is followed by desilylation to give an a-substituted carbonyl compound. The carbocations can be generated from tertiary chlorides and a Lewis acid, such as TiCU. This reaction provides a method for introducing tertiary alkyl groups alpha to a carbonyl. This transformation cannot be achieved by base-catalyzed alkylation because of the strong tendency for tertiary halides to undergo elimination. 

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