This answer is not correct. Remember that the S_N2 mechanism involves a backside attack of the nucleophile on the carbon atom attached to the leaving group with inversion of the groups attached to this carbon atom. In order for the substitution to happen in this case, the electron rich nucleophile would have to blast through the pi electron clouds, take a sharp 90 degree turn and then invert the ring through itself...whew, this would be pretty tough! Note how little room there is inside the ring in the space-filling model.