The present invention relates to novel Substituted Biphenylene Compounds of Formula (I): and pharmaceutically acceptable salts thereof, wherein Y1, Y2, R1, R2, R4, Ra and Rb are as defined herein. The present invention also relates to compositions comprising at least one Substituted Biphenylene Compound, and methods of using the Substituted Biphenylene Compounds for treating or preventing HCV infection in a patient.