# Mechanism of Grignard reaction with 2-(thiiran-2-yl)oxirane

What will be the final major product?

I think $$\ce{R}$$ of $$\ce{RMgX}$$ attacks thiirane ring because negative charge on sulfur is more stable than that of oxygen.

But why doesn't the negative sulfur subsequently attack on less hindered carbon of the ring? Instead, it attacks the β-carbon which is more hindered and opens the ring so that methyl of $$\ce{CH3I}$$ can make bond with negative oxygen atom. Why does the reaction proceed that way?