Synthesis of deuterated morpholine derivatives

1. A process for the preparation of a compound of the formula (I) or a salt thereof,

the process comprising reacting a compound of Formula (II) with an acid to form the compound of Formula (I) or a salt thereof:

wherein:

R 1 is —H, —OH, —NO, —NH 2 , —NHR a , —N(R a ) 2 , —C(═O)NR c R d , —C(═O)OR g ,-phthalimido, —SO 2 —R b , or a group selected from alkyl, aryl, heteroaryl, aralkyl, heteroaralkyl, cycloalkyl, heterocycloalkyl, cycloalkylalkyl, heterocycloalkylalkyl, wherein the alkyl, aryl, heteroaryl, aralkyl, heteroaralkyl, cycloalkyl, heterocycloalkyl, cycloalkylalkyl, and

heterocycloalkylalkyl are each independently optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, —OR e , —C(═O)OR e , —C(═O)R e , —NO 2 , —CN, —NH 2 , —NHR a , —N(R a ) 2 , —NR c C(═O)R e , —C(═O)NR c R d , —S(O)R e , —S(O) 2 R e , —SR e , and —SO 2 NR c R d , wherein each C 1-6 alkyl is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl and C 1-6 haloalkoxy;

each R a is independently an alkyl optionally substituted with halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl or C 1-6 haloalkoxy;

R b is alkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl, each of which is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, —OR e , —C(═O)OR e , —C(═O)R e , —NO 2 , —CN, —NH 2 , —NHR a , —N(R a ) 2 , —NR c C(═O)R e , —C(═O)NR c R d , —S(O)R e , —S(O) 2 R e , —SR e , and —SO 2 NR c R d , wherein each C 1-6 alkyl is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl and C 1-6 haloalkoxy;

R c and R d are each independently —H or alkyl optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, —OR e , —C(═O)OR e , —C(═O)R e , —NO 2 , —CN, —NH 2 , —NHR a , —N(R a ) 2 , —NR c C(═O)R e , —C(═O)NR c R d , —S(O)R e , —S (O) 2 R e , —SR e , and —SO 2 NR c R d , wherein each C 1-6 alkyl is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl and C 1-6 haloalkoxy;

R e is —H or alkyl optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, -OR f , —C(═O)OR f , —C(═O)R f , —NO 2 , —CN, —NH 2 , —NHR a , —N(R a ) 2 , —NR c C(═O)R f , —C(═O)NR c R d , —S (O)R f , —S (O) 2 R f , —SR f , and —SO 2 NR c R d , wherein each C 1 - 6 alkyl substituent is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl and C 1-6 haloalkoxy;

R f is alkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl;

R g is alkyl optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, —OR f , —C(═O)OR f , —C(═O)R f , —NO 2 , —CN, —NH 2 , —NHR a , —N(R a ) 2 , —NR c C(═O)R f , —C(═O)NR c R d , —S (O)R f , —S (O) 2 R f , —SR f , and —SO 2 NR c R d , wherein each C 1-6 alkyl substituent is optionally substituted with one or more groups selected from halogen, C 1-6 alkyl, C 1-6 alkoxy, —OH, C 1-6 haloalkyl and C 1-6 haloalkoxy; and

R 4 , R 4′ , R 5 and R 5′ are each —H.

2. The process of claim 1 , further comprising reacting a compound of Formula (III)

with a reducing agent to form a compound of formula (II) or a salt thereof, wherein each R 2 is D, —OH, or —O(alkyl).

3. The process of claim 2 , wherein R 2 is —OH, or —O(alkyl).

4. The process of any one of claims 1 to 3 , wherein the deuterium enrichment at each position designated as deuterium in the compound of Formula (I) is at least about 85%.

5. The process of any one of claims 1 to 4 , wherein the acid is a Lewis acid or a Bronsted acid.

6. The process of claim 2 or 3 , wherein the reducing agent is selected from diborane-d 6 (B 2 D 6 ), DSiCl 3 , Et 3 SiD, diisobutylaluminum deuteride (DIBAL-D), LiAlD 4 , LiBD 4 , and NaBD 4 .

7. The process of any one of claims 1 to 6 , wherein R 1 is benzyl, —SO 2 -aryl, or —SO 2 -heteroaryl.

8. The process of claim 1 , further comprising the step of removing R 1 from a compound represented by Structural Formula (I) to form an optionally substituted morpholine-2,2,6,6-d 4 represented by Structural Formula (Ia) or a salt thereof:

wherein R 1 is benzyl and the benzyl group is removed under hydrogenation conditions.