Catalytic Activation of Silylated Nucleophiles

Substituted aryl fluorides reacted with TBDMS-OCeITtOMe-p in the presence of 10 mol% Bu-P4 base (Table 5.3). Ethylp-fluorobenzoate reacted at 80 °C to give the biaryl ether in 

92% yield (run 1). Other bases, such as BEMP or DBU, were found almost inactive as a promoter (runs 2, 3). p-Fluorobenzonitrile reacted at 100°C to give the desired product in 92% yield (run 4). p-Fluorobenzotrifluoride also reacted at 100 °C to give the desired product in 93% yield (run 5). When the reaction of o-fluorobromobenzene was carried out at 100 °C in DMF, the substitution occurred only at the fluorine substituted position to give the bromo biaryl ether exclusively in 85% yield (run 6). The reaction of o-iodofluorobenzene was also examined and the iodophenyl aryl ether was obtained in 43% yield (run 7). The reverse and complimentary regioselectivity to transition metal catalysed reactions is attractive for selective functionalization of aromatic compounds [54]. 

The reaction of 2-fluoronitrobenzene with n-hexanol was carried out in the presence of EtsSiH and 10 mol% of Bu-P4 at 100 °C for 2h (Table 5.4, run 1). The arylation reaction proceeded to give the ether quantitatively. The reaction with n-butanol also proceeded smoothly. Secondary alcohols, such as 2-phenylethylalcohol and 2-butanol, were arylated under the same reaction conditions to give ethers in excellent yields (mns 3 and 4). Aryl fluorides with weaker electron-withdrawing groups were then examined. 4-Fluorobenzo-nitrile and 4-fluorobenzotrifluoride were found to be good substrates [55] (runs 5, 6). 

Dictyomedins A and B from Dictyostelium cellular sUme moulds were recently discovered by Oshima and co-workers as physiologically active substances which inhibit their own 

Aryltrimethylsilanes have been used as important synthons and various desilylative functionalizations have been investigated. Among these, anion mediated generation of aryl anions is one of the most important methods for selective bond formation. However, the reaction has been limited to aryltrimethylsilanes with strong electron-withdrawing groups on the aromatic rings. It was found that Bu-P4 base could be used as an excellent catalyst to 

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Other synthetic applications of the phosphazene bases include the use of Bu -Pl (37) in the alkylation of adenine in solution or solid phase, and the catalytic esterification of various glycerol derivatives with fatty methyl esters at room temperature. On occasions, the action of the phosphazene bases may promote processes that other proton abstractors do not, such as the observed rearrangement of (43) to the flavone (44) in the presence of (40e) (OBn = benzoyloxy). Patented process, include the purification " and assembly of polyhedral oligomeric silsesquioxane monomers, and the catalytic activation of silylated nucleophiles. ... 

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