Enamine stannane

Liebeskind and associates converted 3,4-diisopropyl squarate (97) to stannylcyclobutenedione 98 via a 1,4-addition-elimination sequence. 98 was then coupled with 2-iodothiophene to afford substituted cyclobutenedione 99 [85]. In another case, 3-lithioquinuclidin-2-ene, generated from the Shapiro reaction of 3-quinuclidinone (100), was quenched with Bu3SnCl to afford a unique enamine stannane 101. The Stille reaction of stannane 101 and 5-bromo-2-formyl-thiophene then furnished 3-thienylquinuclidine 102 [86]. 

Suitably protected glycosyl halides or acetates, upon Lewis-acid promoted SN1 heterolysis, generate glycosyl cation intermediates that can react with electron-rich arenes, heteroarenes, Me3SiCN, enoxysilanes, enamines, allyl silanes and stannanes, acetylenyl silanes and stannanes affording C-glycosyl compounds. 

The range of carbon nucleophUes that can be used in the catalytic aUyUc substitution reaction is not unlimited. The use of more basic reagents, such as alkylUthiums or cuprates, usually results only in reduction of the aUylic substrate. Malonate derivatives, enol stannanes, enamines, and stable enols, however, can give allylation products. 

In the absence of EIbN, the intermediate iminium cation can be captured with nucleophiles such as silyl ketene acetals, silyl enol ethers, enamines, and aUyl stannanes (eq 40). ... 

---