Alkoxyallylsilanes: Functional Protecting Groups

Allyl-t-butylmethylsilyl groups were shown to function as alcohol protecting groups whose hydrolytic stability was greater than t-butyldimethylsilyl (TBS) and Si(SiMe3)3 (sisyl) groups. Pseudo-first-order rate constants for the acidic hydrolysis of primary, benzylic, and secondary allyl-t-butylmethylsilyl ethers in AcOD/THF-d8/D2O were determined to be 2.94×10−3, 8.26×10−4, and 8.26×10−4 s−1, respectively. The regioselectivity of acidic hydrolysis of allylbenzyloxy-t-butylmethylsilane 1 was examined under strong acid (p-TsOH/CD2Cl2) and weak acid (AcOD/THF-d8/D2O) conditions. In both cases, benzyl alcohol was initially produced exclusively from silicon–oxygen bond cleavage: allylic cleavage was only subsequently observed over time. However, the allyl group of the silyl ether could be hydrosilylated. The resulting alkoxy-functionalized disiloxane had greater hydrolytic stability under acidic conditions than the starting alkoxyallyl-t-butylmethylsilane.