Compositions and methods for treating cns disorders

A compound of Formula (1-III-a), (1-III-b), (1-III-c), or (1-III-d):

• or a pharmaceutically acceptable salt thereof,
• wherein:
• is a single or double bond, provided if a double bond is present, then R5 and one of R6a or R6b are absent;
• each n is independently 1 or 2;
• each X is independently hydrogen, halogen, or 5-6 membered monocyclic heteroaryl having 2-4 nitrogen atoms, wherein the heteroaryl is optionally substituted with one group selected from halo, C1-3 alkyl, —CN, or C1-3 alkoxy;
• R5 is hydrogen or methyl, or when is a double bond, R5 is absent;
• R19 is hydrogen, methyl, ethyl, or unsubstituted cyclopropyl;
• R18 is methyl or ethyl;
• R3 is C1-3 alkyl optionally substituted with C1-3 alkoxy;
• and
• each of R2a, R2b, R4a, R4b, R6a, R6b, R11a, R11b, R16a, and R16b is hydrogen.

A compound selected from the group consisting of:

• Example
• STRUCTURE
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 85
• 86
• 87
• 88
• 89
• 90
• 91
• and
• 92
• or a pharmaceutically acceptable salt thereof.