Pyrrolo [2,3-d] pyrimidine

A compound of Formula I: Formula ** ** or a pharmaceutically acceptable salt thereof; wherein: R1 is selected from the group consisting of hydrogen and (C1-C6); and when R1 is hydrogen then R2 is selected from the group consisting of alkyl (C5-C6), haloalkyl (C1-C6), cycloalkyl (C3-C6) alkyl (C1-C6), hydroxyalkyl (C5-C6) alkyl, (C1-C6) -alkenyl, (C1-C6), phenyl, phenyl (C1-C6), cycloalkyl (C3-C6) heterocyclyl, and heterocyclyl (C1-C6); when R1 is (C1-C6), then R2 is selected from the group consisting of (C1-C6), haloalkyl (C1-C6), cycloalkyl (C3-C6) alkyl (C1-C6), hydroxyalkyl ( C1-C6) alkyl, (C1-C6), phenyl, phenyl (C1-C6), cycloalkyl (C3-C6) heterocyclyl, and heterocyclyl (C1-C6); wherein (C3-C6), wherever it is present, is optionally substituted with one or more substituents selected from the group consisting of hydroxy (C1-C6), phenyl, phenyl (C1-C6) alkoxycarbonylamino (C1 C6 alkyl); and wherein when R1 is hydrogen and R2 is cyclobutyl, then cyclobutyl substituted with one or more substituents selected from the group consisting of hydroxy (C1-C6), phenyl, halophenyl, phenyl (C1-C6) alkoxycarbonylamino (C1-C6); wherein phenyl, wherever present, is optionally substituted with one or more substituents independently selected from the group consisting of cyano, halo, hydroxy, (C1-C6), haloalkyl (C1-C6) cyanoalkyl (C1 C6), alkoxy (C1-C6) alkylaminosulfonyl aminosulfonyl and (C1-C6); wherein heterocyclyl, wherever present, is optionally substituted with one or more substituents independently selected from the group consisting of halo, (C1-C6) alkyl, (C1-C6) amino and (C1-C6 selected ); and wherein the (C1-C6) in phenylalkyl (C1-C6) and heterocyclyl (C1-C6) optionally substituted with a substituent independently selected from the group consisting of halo and hydroxy; and R3 selected from the group consisting of hydrogen and (C1-C6).