Azetidine compounds

A compound of the formula (I),

• an enantiomer thereof, or a pharmaceutically acceptable salt of the compound or enantiomer, wherein:
• Het is selected from the group consisting of:
• A) piperidino, wherein the piperidino is:
• i) substituted with a substituent selected from the group consisting of hydroxy, hydroxyalkyl, oxo, methylthio, methylsulfinyl, methylsulfonyl, cyano, 1,3-dioxolan-2-yl, C1-C4 alkoxy, amino, acylamino, and (C1-C4 alkylsulfonyl)amino,
• wherein the amino is unsubstituted or optionally mono or disubstituted with a substituent selected from the group consisting of C1-C4 alkyl, C3-C4 cycloalkyl, C2-C4 alkenyl, and C2-C4 alkynyl, and
• wherein the acylamino and the (C1-C4 alkylsulfonyl)amino are unsubstituted or optionally N-substituted with a substituent selected from the group consisting of C1-C4 alkyl, C3-C4 cycloalkyl, C2-C4 alkenyl, and C2-C4 alkynyl;
• ii) substituted with one or two fluoro atoms;
• or
• iii) disubstituted by C1-C4 alkyl and/or hydroxy groups;
• B) morpholino or thiomorpholino, wherein the thiomorpholino is unsubstituted or optionally substituted at its sulfur atom by one or two oxygen atoms;
• and
• C) piperazino which is unsubstituted or optionally substituted at the 4-nitrogen atom by a substituent selected from the group consisting of C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C3-C4 cycloalkyl, C1-C4 alkyl sulfonyl, and C1-C4 acyl;
• R1 is hydrogen;
• R2 is fluoro attached at the 4-position;
• R3 is hydrogen;
• R4 is selected from the group consisting of C1-C4 alkyl, C3-C4 cycloalkyl, C2-C4 alkenyl, and C2-C4 alkynyl;
• and
• Ar is phenyl substituted at its 3- and 5-positions by substituents independently selected from the group consisting of halogen, C1-C4 alkyl, C1-C4 alkoxy, cyano, and nitro;
• wherein one or more of the hydrogen atoms of the alkyl, cycloalkyl, alkenyl, alkynyl, and alkoxy groups may be optionally substituted for a fluorine atom.