Compounds of Formula (00A) and salts thereof, wherein R1, R2 R3, R4 and n are defined herein, are useful as inhibitors of one or more Janus kinases. Also provided are pharmaceutical compositions that include a compound of Formula (00A) and a pharmaceutically acceptable carrier, adjuvant or vehicle, and methods of treating or lessening the severity of a disease or condition responsive to the inhibition of a Janus kinase activity in a patient.