Heterocyclic compounds and imaging agents for imaging Huntington protein

A compound of Formula Ila:

• or an isotopically enriched analog, pharmaceutically acceptable salt, tautomer, stereoisomer, or a mixture of stereoisomers thereof,
• wherein the compound is labeled with one or more positron-emitting radioactive isotopes selected from 11C, 13N, 15O, and 18F;
• R23 is hydrogen, halo, cyano, hydroxy, amino, alkylamino, dialkylamino, C1-4alkyl, C1-4haloalkyl, C1-4alkoxy, C1-4haloalkoxy, or C3-6cycloalkyl;
• R3 is methyl;
• each of R11, R12, R13, and R14 is independently hydrogen, halo, cyano, hydroxy, amino, alkylamino, dialkylamino, C1-4alkyl, C1-4haloalkyl, C1-4alkoxy, or C1-4haloalkoxy;
• L is —(C(R6)2)m—, wherein m is 1, 2, 3, or 4;
• each R6 is independently hydrogen, halo, cyano, hydroxy, amino, alkylamino, dialkylamino, C1-4alkyl, C1-4haloalkyl, C1-4alkoxy, or C1-4haloalkoxy;
• or
• two R6, together with any intervening atoms, join to form a 3- to 6-membered ring;
• Ra is hydrogen, C1-6alkyl, or C1-6haloalkyl;
• Rb is -L2-X1;
• L2 is absent;
• X1 is C3-10cycloalkyl, C6-10aryl, heteroaryl, or heterocyclyl, wherein X1 is optionally substituted with 1 to 4 R4;
• and
• each R4 is independently halo, cyano, hydroxy, amino, alkylamino, dialkylamino, C1-4alkyl, C1-4haloalkyl, C1-4alkoxy, or C1-4haloalkoxy;
• or Ra and Rb, along with any intervening atoms, form a 3- to 10-membered heterocyclyl ring optionally substituted by 1 to 4 R4.