The invention relates to thieno-pyridinone derivatives of formula (I), pharmaceutically acceptable salts thereof and pharmaceutical compositions wherein, R1, R2, R3,  R4, X1 and X2 defined herein. The present invention also relates to compositions which comprise antiviral compounds of the invention or a pharmaceutically  acceptable salt thereof, and a pharmaceutically acceptable carrier, optionally in combination. The compounds of the invention are useful in the methods described  herein for reducing/treating viral infections particularly coronavirus infections caused by SARS-CoV, MERS-CoV and SARS-CoV-2.