Stereochemistry of Heterogeneous Asymmetric Catalytic Hydrogenation

11 Stereochemistry of Heterogeneous Asymmetric Catalytic Hydrogenation KAORU HARADA

Downloaded by RUTGERS UNIV on March 8, 2016 | http://pubs.acs.org Publication Date: April 28, 1982 | doi: 10.1021/bk-1982-0185.ch011

University of Tsukuba, Department of Chemistry, Ibaraki 305, Japan

In this paper, the stereochemistry of heterogeneous catalytic hydrogenation of C=N- and C=O double bonds of the derivatives of α-keto acids, keto alco hols and diketones is described. The steric course could be explained by the chelation hypothesis. In 1961, H i s k e y e t a l . ( 1 ) r e p o r t e d t h e s u c c e s s f u l asymmetric s y n t h e s e s o f α-amïho a c i d s . They demons t r a t e d t h e s y n t h e s i s o f amino a c i d s i n 45-70% e n a n t i o m e r i c p u r i t y by c a t a l y t i c hydrogénation o f t h e S c h i f f bases p r e p a r e d from α-keto a c i d s and o p t i c a l l y a c t i v e α-methylbenzylamine f o l l o w e d by h y d r o g e n o l y s i s (Scheme 1 ) . When (S)-amine was used, (S)-α-amino a c i d r e s u l t e d . This i s a highly stereoselective reaction. However, the a u t h o r s d i d n o t d i s c u s s t h e s t e r i c c o u r s e o f t h e asymmetric hydrogénation p r o c e s s . Scheme 1 R-C-COOH " Ν C H -CH-CH (S) 6

5

3

n

R-CH-COOH L NH

H 2

Pd/C ' C H - C H - C H 6

5

3

n

Pd

(S) R-CH-COOH I

H 2

(OH)'

2

L a t e r M i t s u i e t al.(2) r e p o r t e d t h e asymmetric s y n t h e s e s o f p h e n y l g l y c i n e by t h e H i s k e y t y p e r e a c t i o n and p r o p o s e d a s t e r i c c o u r s e f o r t h e asymmetric s y n t h e s i s as shown i n Scheme 2. I f i t i s a p p l i c a b l e t o a l l o f t h e H i s k e y t y p e r e a c t i o n s , t h e f o l l o w i n g may be e x p e c t e d : (a) an i n c r e a s e i n o p t i c a l y i e l d upon s u b s t i t u t i o n o f α-methylbenzylamine by α-ethylbenzylamine and (b) a comparable o p t i c a l y i e l d upon s u b s t i t u t i o n o f α-methylbenzylamine by a - ( 1 - n a p h t h y 1 ) e t h y l a m i n e . 0097-6156/82/0185-0169$05.00/0 © 1982 American Chemical Society

Eliel and Otsuka; Asymmetric Reactions and Processes in Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

ASYMMETRIC

170

REACTIONS

A N D PROCESSES

IN

CHEMISTRY

Scheme 2 C,H 6 5

COOH /

C

X

CH

3


N

0

.

(S) C

C.H . COOH 6 5 / C H I NH ^

N

C if Ν

;C

H

C.H,. COOH 6 5 / C H II 2 Ν >^(S)

H

C

6 5

H

6 5

C H

3

9 2 r

H

C

H

6 5

C H

COOH I Η,Ν-j-H

3

In o r d e r t o examine t h e s t e r i c c o u r s e proposed by M i t s u i e t a l . , we have performed asymmetric s y n t h e s e s o f a l a n i n e , α-aminobutyric a c i d , p h e n y l g l y c i n e , p h e n y l a l a n i n e and g l u t a m i c a c i d from t h e c o r r e s p o n d i n g a-keto a c i d s u s i n g (S) -α-methylbenzylamine [Me (-) ] , (S) - a ethylbenzylamine [ E t ( - ) ] and ( R ) - a - ( 1 - n a p h t h y l ) e t h y l amine [Naph(-)] as t h e c h i r a l a d j u v a n t . The r e s u l t s a r e shown i n T a b l e 1(3^,4). The r e s u l t s i n d i c a t e t h a t a) t h e o p t i c a l p u r i t y o f amino a c i d s o b t a i n e d w i t h α-methylbenzylamine i s always h i g h e r than when α-ethylbenzylamine i s used, b) t h e o p t i c a l p u r i t y o f t h e amino a c i d s d e c r e a s e s s t e a d i l y as t h e b u l k o f t h e a l k y l group o f t h e α-keto a c i d s i n c r e a s e s , and c) t h e o p t i c a l p u r i t y i n c r e a s e s when ( R ) a-(1-naphthyl)ethylamine i s used(£) . These f i n d i n g s show c l e a r l y t h a t t h e s t e r i c c o u r s e proposed p r e v i o u s l y does n o t e x p l a i n any o f t h e e x p e r imental r e s u l t s . Based on m o l e c u l a r models we p r o posed a d i f f e r e n t s t e r i c c o u r s e c o n s i s t e n t w i t h t h e experiments. S t r u c t u r e I (Scheme 3) r e p r e s e n t s a con f o r m a t i o n o f t h e s u b s t r a t e which s a t i s f i e s a l l o f t h e Table I

Asymmetric S y n t h e s i s o f Amino A c i d s

α-Keto a c i d R-CO-COOH R= C H

2

C

5

H

6 5

C H

C

H

2" 6 5

(CH ) COOH 2

2

Solvent:EtOH

Amino

acid

Optical purity(%)

Alanine Alanine Alanine

67 52 83

Butyrine Butyrine

44 33

Me (-) E t (-)

(S) (S) (R) (S) (S)

Me (-) E t (-)

(S) P h e n y l g l y c i n e (S) P h e n y l g l y c i n e

30 24

Me (-) E t (-)

(S) P h e n y l a l a n i n e (S.) P h e n y l a l a n i n e

14 10

Me (-) E t (-)

(S) G l u t a m i c (S.) G l u t a m i c

12 6

Me (-) E t (-) Naph(+)

3

C H

Optically a c t i v e amine

acid acid


HARADA

11.

Heterogeneous

Asymmetric

Catalytic

Hydrogénation

Scheme 3 H R (S) ι \ I

C

H

R I

0

6 5

HN

( I )

C

0

0

H

2

^(S)

2

Scheme 4


H

R

C

C C

H

6 5

N

^

CH

0

y° (Pd)'n

H

(ID

-C

3

R

Ρ

C

C

V "(Pdfn

(III

—

c o n d i t i o n s r e q u i r e d by the e x p e r i m e n t a l f i n d i n g s (_3) · The s t r u c t u r e I might be c o n s i d e r e d t o form a sub s t r a t e - c a t a l y s t complex as shown i n s t r u c t u r e I I (Scheme 4 ) . A m o l e c u l a r model o f s t r u c t u r e I I f i t s v e r y w e l l on the s u r f a c e o f the p a l l a d i u m c a t a l y s t . The p l a n e c o m p r i s i n g the S c h i f f base o f the α-keto a c i d i s assumed t o be p e r p e n d i c u l a r t o the p a l l a d i u m s u r f a c e , w i t h the p h e n y l group l y i n g on the p a l l a d i u m s u r f a c e as shown i n s t r u c t u r e I I . I f the p h e n y l group was p l a c e d as shown i n s t r u c t u r e I I I (Scheme 4 ) , the a l k y l group o f the asymmetric m o i e t y and t h a t o f the k e t o a c i d would i n t e r f e r e w i t h each o t h e r , and the s t r u c t u r e I I I would be u n s t a b l e . Thus we assume (A) the sub s t r a t e i n i t i a l l y i n t e r a c t s w i t h the c a t a l y s t , t o form a s u b s t r a t e - c a t a l y s t complex as shown i n s t r u c t u r e I I b e f o r e the c a t a l y t i c hydrogénation t a k e s p l a c e , and t h e n (B) the s t r u c t u r e I I i s adsorbed on the c a t a l y s t from the l e s s b u l k y s i d e o f the m o l e c u l e , and c a t a l y t i c hydrogénation t a k e s p l a c e . We have c a l l e d t h i s hydrogénation p r o c e s s "the c h e l a t i o n h y p o t h e s i s " ( 3 ) / and f u r t h e r s t u d i e s were u n d e r t a k e n t o t e s t t h i s hypothesis. T a b l e I I shows s o l v e n t e f f e c t s i n t h e asymmetric s y n t h e s i s o f a l a n i n e from p y r u v i c a c i d and ( S ) - a methylbenzylamine(A). The o p t i c a l p u r i t y o f a l a n i n e decreases with i n c r e a s i n g p o l a r i t y of the s o l v e n t . In the c a s e o f t h e asymmetric s y n t h e s i s o f g l u t a m i c a c i d from α-keto-glutaric a c i d and (S)-α-methylbenzylamine, the c o n f i g u r a t i o n o f t h e r e s u l t i n g g l u t a m i c a c i d was a c t u a l l y i n v e r t e d by the use o f p o l a r s o l v e n t s . The s u b s t r a t e appears t o i n t e r a c t w i t h the c a t a l y s t more s t r o n g l y i n a l e s s p o l a r t h a n i n a more p o l a r s o l v e n t . Thus, the p o p u l a t i o n o f the c h e l a t e d s u b s t r a t e i s


ASYMMETRIC

172 Table

II

A N D PROCESSES

S o l v e n t E f f e c t i n t h e Asymmetric of Alanine

Solvent


REACTIONS

Yield(%)

CHEMISTRY

Synthesis

Optical purity(%)

Hexane

75

75

AcOEt

49

60

DMFA

47

50

i-PrOH

56

46

MeOH

61

38

MeOH:H 0(l:2) 2

75

35

MeOH:H 0(l:4)

76

29

2

IN

l a r g e r i n t h e l e s s p o l a r s o l v e n t than i n t h e more p o l a r one. The u n c h e l a t e d s p e c i e s , which has a s t a b l e conf o r m a t i o n IV (Scheme 5 ) i n s o l u t i o n , c o u l d be adsorbed on t h e l e s s b u l k y f r o n t -C=N- f a c e o f t h e m o l e c u l e (Scheme 5 ) r e s u l t i n g i n an a l a n i n e d e r i v a t i v e which has the c o n f i g u r a t i o n o p p o s i t e t o t h a t o b t a i n e d from t h e chelated species. Asymmetric c a t a l y t i c hydrogénation o f t h e S c h i f f base p r e p a r e d from e t h y l p y r u v a t e and an o p t i c a l l y a c t i v e amine i n d i f f e r e n t s o l v e n t s was c a r r i e d o u t and supports the c h e l a t i o n hypothesis. F i g u r e 1 shows s o l v e n t e f f e c t s i n t h e s y n t h e s i s o f a l a n i n e and a a m i n o b u t y r i c a c i d (5^) . When (£) - b e n z y l i c amine was used as t h e asymmetric m o i e t y , t h e o p t i c a l p u r i t y o f t h e r e s u l t i n g amino a c i d i n c r e a s e d w i t h a d e c r e a s e i n s o l vent p o l a r i t y ( £ , 7 J · temperature e f f e c t was a l s o o b s e r v e d , and t h e o p t i c a l p u r i t y o f t h e amino a c i d s i n c r e a s e d upon l o w e r i n g t h e r e a c t i o n t e m p e r a t u r e ( £ , 9 ^ A

10 ) . The c h e l a t i o n h y p o t h e s i s c o u l d a l s o be a p p l i e d t o the c a t a l y t i c hydrogénation o f α-keto a c i d amides c a r r i e d o u t i n i t i a l l y by H i s k e y e t a l . , who e x p l a i n e d the s t e r i c c o u r s e assuming i n t e r m e d i a t e s t r u c t u r e V ( 1 1 ) (Scheme 6 ) . Scheme 5 H 1

C H> 6

5

R \ N

%

Ο polar solvent

c

^0 (Pd)n—

(S) amino a c i d

less polar solvent

υ R'^ C H 6 5

R £ N

,0 0~

(IV)

(R) amino a c i d


HARADA

11.

Figure

Heterogeneous

Asymmetric

Catalytic

Hydrogénation

173

S o l v e n t E f f e c t i n t h e Asymmetric S y n t h e s i s o f Amino A c i d s from E t h y l P y r u v a t e ( 5 )

1


Amine (R)-(+) - a - M e t h y l b e n z y l (SM-) -a-Methylbenzyl (RM+) - a - E t h y l b e n z y l (R)-(+) -1- (a-Naphthyl) ethyl (S)-(-) - a - M e t h y l b e n z y l (S)-(-) - a - M e t h y l b e n z y l (a)-(e), Alanine ( f ) , a-Aminobutyric acid

Product

Catalyst:

(a)-(d) , P d ( 0 H ) / C (e) (f) , Pd/C 9

z

Dielectric of Solvent

Constant

Scheme 6 R-N CH

34Ο

Η

R-N

\

*C/

NH

„„f

NH

i C 3

0

J Η CH3

(V)

Pd/C

-o-cCH

/

CHo

N 2

/ \

•c

COOH /

c-..„ 0

CH^

3

The change i n c o n f i g u r a t i o n o f t h e r e s u l t i n g amino a c i d w i t h t h e use o f d i f f e r e n t asymmetric m o i e t i e s i s a l s o e x p l a i n e d by the c h e l a t i o n h y p o t h e s i s ( 1 2 ) (Scheme 7 ) . I n t h e s e q u e l , we w i l l d i s c u s s a g e n e r a l i z a t i o n o f the c h e l a t i o n h y p o t h e s i s as i t a p p l i e s t o r e a c t i o n s o t h e r t h a n hydrogénation o f S c h i f f bases o f α-keto a c i d s w i t h c h i r a l amines. The c a t a l y t i c hydrogénation o f p y r u v i c a c i d amide r e s u l t e d i n the f o r m a t i o n o f l a c t a m i d e i n h i g h o p t i c a l p u r i t y (75-99% d i a s t e r e o m e r i c excess)(13). T h i s might be e x p l a i n e d by the c h e l a t e c o n f o r m a t i o n o f the s u b s t r a t e - c a t a l y s t complex shown i n Scheme 8. The c a t a l y t i c hydrogénation o f o p t i c a l l y a c t i v e b e n z o i n oxime r e s u l t e d i n t h e s t e r e o s e l e c t i v e f o r m a t i o n of o p t i c a l l y a c t i v e erythro diphenylethanolamine in


ASYMMETRIC

174

REACTIONS

Scheme 7 ?3 /? .COOiBu

CH

C

,

C

/~ \/\-CH

Bzl-N^ ,NH \ * 'n~"

— H

3

A N D PROCESSES

C

N - f "

Η

N

λ

Ν

(pdi

3

2

3


Z

2

H

t

N

H

2

CH (R)64%ee 3

Scheme 8 CH\ _ • 0 R I (§)

2N

H

H

H

3

5

c

2

n

Ο

H

CH Ο ,C H ÇOOH 2 \ c _ ' /-icSoiBu H I — «g V \ — - 3 (S)41%ee

5

C 0 0 l B u H

C

COOH

A - C H 3 —

H

CH Ο CH >- f c^B 1-/ > \ — (Pd) —

CHEMISTRY

Ο COOiBu

3

2

IN

3

CHo

2

^Ο R, (,„ S) x

.NH \ H / (S) V \ H (Pd),η 75 - 99%(§-S) high optical and diastereomeric purity(14) (Scheme 9). Benzil monoxime was similarly hydrogenated using a palladium catalyst to form erythro diphenylethanolamine (15). If the conformation of the substrate in the reaction is planar, as expected from steric and elec tric considerations, the resulting hydrogénation product should be the threo isomer(16) (Scheme 10). In Scheme 9 C H^ 6

E

χ

#

6

( § )

C *5

/

\

6

2

H

/N-OH

(Pd) n

H 0

Ç H

6

""/~\ H 0

P d / C

5

Ρα/C'

6

5

5

H-C-OH (S) erythro H-C-NH (R) 85 - 90 % (S-R) I 2

65 H

Scheme 10 Ç H 6

5

HO-C-H + I H-C-NH CH racemic threo isomer 2

6


5

HARADA


11.

Heterogeneous

Asymmetric

Catalytic

Hydrogénation

175

f a c t , however, the r e s u l t i n g d i p h e n y l e t h a n o l a m i n e was found t o be p r e d o m i n a n t l y the e r y t h r o form. S i m i l a r r e s u l t s have been r e p o r t e d i n the s y n t h e s i s o f t h r e o n i n e , p h e n y l s e r i n e and ephedrine(17-21) (Scheme 11). I n 1953 Chang and Hartung p r o p o s e d a mechanism f o r the hydrogénation o f d i k e t o n e monoxime which e x p l a i n s the f o r m a t i o n o f a s i n g l e racemic m o d i f i c a t i o n ( e r y t h r o form) by the f o r m a t i o n o f a r i g i d r i n g - l i k e s t r u c t u r e w i t h the c a t a l y s t (22) . The e x p l a n a t i o n c o u l d be r e g a r d e d as a c h e l a t i o n h y p o t h e s i s p r e c e d i n g t h e present generalized c h e l a t i o n hypothesis i n c a t a l y t i c hydrogénation. R e c e n t l y , s u p p o r t f o r the c h e l a t i o n h y p o t h e s i s was o b t a i n e d by examining the i n f r a r e d d i c h r o i s m o f t h e s u b s t r a t e a d s o r b e d on a m e t a l s u r f a c e u s i n g t h e h i g h s e n s i t i v i t y r e f l e c t i o n method(23-26). I n t h e s e i n v e s t i g a t i o n s the o r i e n t a t i o n o f the s u b s t r a t e on the m e t a l s u r f a c e i s j u s t as assumed by the c h e l a t i o n h y p o t h e s i s . I t was found t h a t the OH, C=0, NH~, =NOH groups i n t e r a c t w i t h the m e t a l s u r f a c e and the s u b s t r a t e s s t a n d on the c a t a l y s t s u r f a c e v e r t i c a l l y . The o b s e r v a t i o n o f the i n f r a r e d d i c h r o i s m i s c o n s i d e r e d t o be a d i r e c t p h y s i c a l e v i d e n c e f o r the c h e l a t i o n h y p o t h e s i s (Scheme 12). Scheme 11 C*H 6 5 rt

C

CH

H

, 6 5 •C

COOEt /

3

HO-N

•c w

C//

w

6

6

N-OH

,0 M

C H

n

65

C »5

M

M

CH

5

CH-

3

F^COOEt

->c—c'

C H5

.COOEt -C \ NH-Ac

6

H

HO

/

\

0

N-CH,

NH-Ac M

M

M Scheme 12 C

H 6

5 S

CH, CH

OH

2

H-^C-C

7

,0

H.V,•C—C J +/ H N^

\ .0'

3

HO

7

\ (Ni) C Hc "COOEt fi

(Ni), CH-

C—c

C—C

// 0

OEt

% ,ΝΟΗ *(Pd)'

//

% ,0

HON^ N

(Pdf'-



176

ASYMMETRIC REACTIONS AND PROCESSES IN CHEMISTRY

Literature Cited 1. Hiskey,R.G.; Northrop,R.C. J. Am. Chem. Soc. 1961, 83, 4798. 2. Kanai,A.; Mitsui,S. J. Chem. Soc. Jpn. (Pure Chem. Sec.) 1966, 89, 183. 3. Harada,K.; Matsumoto,K. J. Org. Chem. 1967, 32, 1794. 4. Harada,K.; Matsumoto,K. J. Org. Chem. 1968, 33, 4467. 5. Harada,K.; Yoshida,T. B u l l . Chem. Soc. Jpn. 1970, 43, 921. 6. Harada,K.; Kataoka,Y. Tetrahedron Lett. 1978, 2103. 7. Harada,K.; Tamura,M. B u l l . Chem. Soc. Jpn. 1979, 52, 1227. 8. Harada,K.; Yoshida,T. J. Chem. Soc. Chem. Commun. 1970, 1071. 9. Harada,K.; Yoshida,T. J. Org. Chem. 1972, 37, 4366. 10. Harada,K.; Kataoka,Y. Chem. Lett. 1978, 791. 11. Hiskey,R.G.; Northrop,R.C. J. Am. Chem. Soc. 1965, 87, 1753. 12. Harada,K.; Matsumoto,K. B u l l . Chem. Soc. Jpn. 1971, 44, 1068. 13. Harada,Κ.; Munegumi,Τ.; Nomoto,S. Tetrahedron Lett. 1981, 22, 111. 14. Harada,Κ.; Shiono,S.; Nomoto,S. unpublished result. 15. Ishimaru,T. J. Chem. Soc. Jpn. (Pure Chem. Sec.) 1960, 81, 643. 16. Harada,K. In "The Chemistry of the Carbon-nitrogen Double Bond"; Patai,S., E d . ; Interscience Publishers: London, 1970; pp 255-298. 17. Albertson,N.F.; T u l l a r , B . F . ; King,J.A. J. Am. Chem. Soc. 1948, 70, 1150. 18. Pfister,K.; Robinson,C.A.; Schabica,A.C.; Tishler, M. J. Am. Chem. Soc. 1948, 70, 2297. 19. Pfister,K.; Robinson,C.A.; Schabica,A.C.; Tishler, M. J. Am. Chem. Soc. 1949, 71, 1101. 20. Bolhofer,W.A. J. Am. Chem. Soc. 1952, 74, 5459. 21. Freudenberg,K.; S c h ö f f e l , E . ; Braun,E. J. Am. Chem. Soc. 1932, 54, 234. 22. Chang,Y.; Hartung,W.H. J. Am. Chem. Soc. 1953, 75, 89. 23. Hatta,A.; Suëtaka,W. B u l l . Chem. Soc. Jpn. 1975, 48, 2428. 24. Hatta,A.; Moriya,Y.; Suëtaka,W. B u l l . Chem. Soc. Jpn. 1975, 48, 3441. 25. Osawa,M.; Hatta,A.; Harada,K.; Suëtaka,W. B u l l . Chem. Soc. Jpn. 1976, 49, 1512. 26. Suëtaka,W.; Harada,Κ. unpublished result. RECEIVEDJanuary 4, 1982.


Stereochemistry of Heterogeneous Asymmetric Catalytic Hydrogenation

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