| The stereochemistry of the lithium/tin exchange was investigated in ether and tetrahydrofuran (THF). The exchange was shown to occur with retention of configuration at tin in ether and epimerization of configuration in THF. The mechanistic implication is that the cleavage occurs through a four-centered transition state in ether; however, in THF a pseudorotating, pentacoordinate tin "ate" complex has a sufficient lifetime to cause epimerization at tin. Reaction of 3-methyl-3-(exo-phenyl)-3-stannabicyclo (3.2.1) octane or 3-methyl-3-(endo-phenyl)-3-stannabicyclo (3.2.1) octane with 2 equiv of p-tolyllithium (;The individual solvated ions (RLi(HMPA)... |
