β2-adrenergic receptor agonists

1. A process for preparing a compound of formula (II′):

wherein

Ar 1 and Ar 3 are independently selected from phenyl, 4-hydroxy-3-hydroxymethylphenyl, 4-hydroxy-3-(HCONH-)phenyl, 3,5-dichloro-4-aminophenyl, and

or a protected derivative thereof;

wherein the stereochemistry at *C is (R), (S), or (RS);

W is alkylene;

Ar 2 is 1,4-phenylene;

X is a bond;

Q is —N(R z )—CH 2 —**CH(OH)-, wherein the stereochemistry at **C is (R), (S), or (RS); and

R x and R z are each hydrogen or R x and R z are each PG 1 , wherein PG 1 is an amino protecting group;

or a salt thereof;

the process comprising:

(a) deprotecting a compound of formula (II′) wherein Ar 1 or Ar 3 are protected derivatives;

(b) deprotecting a compound of formula (II′) wherein R x and R z are each PG 1 ;

(c) (i) reacting a compound of formula (1):

 with a compound of formula (2):

H 2 N—W—Ar 2 —NH 2   (2)

 to form a reaction mixture;

(ii) adding a compound of formula (1′):

to the reaction mixture of step (c)(i); then adding a reducing agent;

(d) reacting a compound of formula (1) with a compound of formula (a):

 then adding a reducing agent;

(e) reacting a compound of formula (a) with a compound of formula (b):

(f) when Ar 1 and Ar 3 are the same, reacting a compound of formula (1) with a compound of formula (2); then adding a reducing agent;

and for steps (a), (b), (c), (d), (e), and (f), optionally removing any protecting groups;

to provide a compound of formula (II′) or a salt thereof.

2. The process of claim 1 , wherein Ar 1 and Ar 3 are independently selected from phenyl, 4-hydroxy-3-hydroxymethylphenyl, 4-hydroxy-3-(HCONH-)phenyl, 3,5-dichloro-4-aminophenyl,

4-benzyloxy-3-(methoxycarbonyl)phenyl, and 4-hydroxy-3-(methoxycarbonyl)phenyl.

3. The process of claim 1 , wherein W is ethylene.

4. The process of claim 3 , wherein Ar 1 is phenyl, 4-hydroxy-3-hydroxymethylphenyl, 4-hydroxy-3-(HCONH-)phenyl, 4-benzyloxy-3-(methoxycarbonyl)-phenyl, or 4-hydroxy-3-(methoxycarbonyl)phenyl.

5. The process of claim 4 , wherein Ar 3 is phenyl or 4-hydroxy-3-hydroxymethylphenyl.

6. The process of claim 5 , wherein R x and R z are each hydrogen.

7. The process of claim 5 , wherein R x and R z are each PG 1 .

8. The process of claim 7 , wherein PG 1 is benzyl.

9. The process of claim 1 , wherein the stereochemistry at *C is (RS).

10. The process of claim 1 , wherein the compound of formula (b) is 4-benzyloxy-3-methoxycarbonylstyreneoxide.

11. The process of claim 1 , wherein the process comprises step (a) or step (b); and optionally removing any protecting groups; to provide a compound of formula (II′).

12. The process of claim 1 , wherein the reducing agent is selected from borane dimethylsulfide complex, sodium cyanoborohydride, lithium aluminum hydride, hydrogen in the presence of palladium, sodium borohydride, borane tetrahydrofuran complex, lithium borohydride, trihydroborane, and catechol borane.

13. A process for preparing a compound of the formula (a′):

or a salt thereof;

wherein

W is alkylene;

Ar 2 is 1,4-phenylene;

wherein the stereochemistry at **C is (R), (S), or (RS);

Ar 3 is selected from phenyl, 4-hydroxy-3-hydroxymethylphenyl, 4-hydroxy-3-(HCONH-)phenyl, 3,5-dichloro-4-aminophenyl, and

or a protected derivative thereof;

R x , R y , and R z are each hydrogen; or R x and R z are hydrogen and R y is PG 2 ; or R x is hydrogen, R y is PG 2 , and R z is PG 1 ; wherein PG 1 and PG 2 are amino protecting groups;

the process comprising:

(a) reacting a compound of the formula (2′):

 with a compound of the formula (b′):

(b) reacting a compound of formula (2′) with a compound of formula (1′):

then adding a reducing agent;

to provide a compound of formula (a′) or a salt thereof.

14. The process of claim 13 , wherein the process further comprises:

removing any protecting groups, PG 1 or PG 2 , to provide a compound of formula (a) wherein R x , R y , and R z are each hydrogen.

15. The process of claim 13 , wherein Ar 3 is phenyl or 4-hydroxy-3-hydroxymethylphenyl.

16. The process of claim 15 , wherein W is ethylene.

17. The process of claim 16 , wherein compound (2′) is 2-(4-aminophenyl)-ethylamine.

18. The process of claim 17 , wherein the process comprises step (a) and the compound of formula (b′) is (R)-styreneoxide or (S)-styreneoxide.

19. The process of claim 16 , wherein R x and R z are hydrogen and R y is PG 2 ; or R x is hydrogen, R y is PG 2 , and R z is PG 1 .

20. The process of claim 19 , wherein PG 1 is benzyl and PG 2 is tert-butoxy-carbonyl.