Silacyclopropanes as Important Synthetic Intermediates

Goals low temperature, broad functional group tolerance 

4 SILVER-MEDIATED TRANSFER OF DI-terf-BUTYLSILYLENE TO OLEFINS 

Exploration of the reactivity of cyclohexene silacyclopropane led Woerpel and coworkers to discover that the inclusion of metal salts enabled silylene transfer to monosubstituted olefins at reduced temperatures (Table 7.1).11,74 A dramatic reduction in the temperature of transfer was observed when cyclohexene silacyclopropane was exposed to copper, silver, or gold salts. Silver salts were particularly effective at decomposing 58 (entries 6-11). The use of substoichiometric quantities of silver triflate enabled ra-hexene silacyclopropane 61 to be formed quantitatively at —27°C (entry 6). The identity of the counterion did affect the reactivity of the silver salt. In general, better conversions were observed when noncoordinating anions were employed. While the reactivity differences could be attributed to the solubility of the silver salt in toluene, spectroscopic experiments suggested that the anion played a larger role in stabilizing the silylenoid intermediate. 

TABLE 7.1. Effect of a Metal Salt on the Temperature of Di-terf-Butylsilylene Transfer 

This functionalization was limited to the formation of 1,3-substituted oxasilacyclopentanes, as exposure of the in situ-generated silacyclopropane to substoichiometric amounts of copper salts did not produce the complementary 1,2-disubstituted oxasilacyclopentanes. 

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