1197420-60-2Relevant academic research and scientific papers
γ-silyl cyclobutyl carbocations
Creary, Xavier,Kochly, Elizabeth D.
supporting information; experimental part, p. 9044 - 9053 (2010/03/04)
(Graph Presented) A series of 3-trimethylsilyl-1-substituted cyclobutyl trifluoroacetates have been prepared and reacted in CD3CO 2D. Rate data indicate that the substrates with the trimethylsilyl group cis to the leaving group react with assistance due to γ-silyl participation. Rate enhancements range from a factor of 209 for α-phenyl-substituted cations to 4.6 × 104 for α-methyl-substituted cations to >1010 for the unsubstituted γ-trimethylsilylcyclobutyl cation. Acetate substitution products are formed with net retention of stereochemistry. These experimental studies, as well as B3LYP/6-31G* computational studies, are consistent with the involvement of carbocations where the rear lobe of the γ-Si-C bond interacts strongly with the developing cationic center. Solvolytic rate studies, as well as computational studies, suggest that the secondary γ-trimethylsilylcyclobutyl cation is even more stable than the β-trimethylsilylcyclobutyl cation, i.e., the γ-silyl effect actually outweighs the potent β-silyl effect. Although computational studies suggest the existence of certain isomeric cations, where the front lobe of the Si-C bond interacts with the cationic center, solvolytic evidence for the involvement of these front lobe stabilized cations is less compelling.
