Grignard vs organolithium reagent opening cyclohexene oxide
$\ce{RLi}$ is much more reactive than $\ce{RMgBr}$ and attacks through the SN2 process, thus inversion of configuration occurs. But in case of $\ce{RMgBr}$, $\ce{MgBr-}$ coordinates with epoxide O atom and forms carbocation on the adjacent carbon. Then a $\ce{C-C}$ bond migrates and the above product is formed.