A compound of Formula I, enantiomers, diastereomers, tautomers or pharmaceutically acceptable salts thereof, wherein R1, R2, R3, R4 and R5 are defined herein, are useful as JAK kinase inhibitors. A pharmaceutical composition that includes a compound of Formula I 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 JAK kinase activity in a patient are disclosed.