Provided is a compound of formula (I) or a pharmaceutically acceptable salt thereof, in which R1, R2, R3, R4, R5, X1, X2, and n are described herein. Also provided is a method of treating an estrogen-mediated disease requiring inhibition of estrogen receptor alpha (ER-alpha), such as cancer, in a subject or inhibiting ER-alpha in a cell with the compound of formula (I) or a pharmaceutically acceptable salt thereof.