The preprojective algebra $P$ of a quiver $Q$ has a family of ideals $I_w$ parametrized by elements $w$ in the Coxeter group $W$. For the factor algebra $P_w = P/I_w$, I will discuss tilting and cluster tilting theory for Cohen-Macaulay $P_w$-modules following works by Buan-I-Reiten-Scott, Amiot-Reiten-Todorov and Yuta Kimura.