Asymmetric Reactions and Processes in Chemistry - American

9 Asymmetric Carbon-Carbon Bond Formation Using Enantiomerically Pure Vinylic Sulfoxides G A R Y H. POSNER, JOHN P. MALLAMO, K Y O MIURA, and MARTIN H U L C E

Asymmetric Reactions and Processes in Chemistry Downloaded from pubs.acs.org by COLUMBIA UNIV on 01/22/18. For personal use only.

Johns Hopkins University, Department of Chemistry, Baltimore, MD 21218

A new, general method is developed for prepara tion of various 3-substituted carbonyl compounds of high enantiomeric purity. Application of this method is made to asymmetric synthesis of either enantiomer of 3-methylalkanoic acids, of enantio merically pure 3-methylcyclopentanone, 3-methyl cyclohexanone, 3-naphthylcyclopentanone 16 and 3-vinylcyclopentanone 18. 9,11-Seco steroid 16 and steroid intermediate 18 are precursors of enantiomerically pure steroids equilenin and estrone of natural absolute configuration. The basis for this asymmetric synthetic method rests on the transfer of chirality from the sulfoxide sul fur atom to the β-carbon carbon atom during organo metallic β-addition to enantiomerically pure αcarbonyl α,β-ethylenic sulfoxides, and the amount of asymmetric induction is highest (i.e., >98%) with cyclopentenone sulfoxide (S)-(+)-10. Stimulated by the o p t i c a l a c t i v i t y of most n a t u r a l l y - o c c u r r i n g compounds and by the complete asymmetric i n d u c t i o n i n most chemical r e a c t i o n s o c c u r r i n g i n b i o l o g i c a l systems, organic chemists have long sought ways t o prepare o p t i c a l l y a c t i v e com pounds d i r e c t l y without using r e s o l u t i o n techniques and ways t o mimic the absolute s t e r e o c o n t r o l i n enzymic r e a c t i o n s . I n recent y e a r s , progress i n t h i s area of asymmetric s y n t h e s i s has been e x t r a o r d i n a r y (1). Two i n d u s t r i a l l y important nrocesses exem p l i f y i n g t h i s type o f recent advance i n c l u d e asymmetric c a t a l y t i c hydrogénation u s i n g c h i r a l rhodium complexes (2) and asymmetric s t e r o i d s y n t h e s i s using n a t u r a l amino a c i d s as c h i r a l d i r e c t o r s (3). Many l i t e r a t u r e r e p o r t s w i t h i n the past 5 years document the phenomenal success of the organic chemist i n a c h i e v i n g o f t e n very h i g h asymmetric i n d u c t i o n s during formation o f carbon-carbon bonds v i a n u c l e o p h i l i c a d d i t i o n t o e l e c t r o p h i l i c o l e f i n s ( l c , d , 4 ) . 0097-6156/82/0185-0139$05.00/0 © 1982 American Chemical Society


140

ASYMMETRIC

REACTIONS

A N D PROCESSES

IN

CHEMISTRY

During the past three years, we have had e x c e l l e n t success i n a c h i e v i n g some asymmetric syntheses (5). We have focused a t t e n t i o n s p e c i f i c a l l y on f a i t h f u l t r a n s f e r of c h i r a l i t y from the s u l f u r atom of some a-carbonyl α,β-ethylenic s u l f o x i d e s to the 3carbon atom during organometallic 3-addition r e a c t i o n s . T h i s type of high asymmetric i n d u c t i o n i n forming carbon-carbon bonds has l e d to s u c c e s s f u l p r e p a r a t i o n of s e v e r a l c l a s s e s of o p t i c a l l y a c t i v e s y n t h e t i c intermediates such as 3-methylalkanoic a c i d s and 3-methylcycloalkanones. In a d d i t i o n , t h i s asymmetric methodology has been a p p l i e d s u c c e s s f u l l y to p r e p a r a t i o n of more complex, e n a n t i o m e r i c a l l y pure molecules such as s t e r o i d s and s t e r o i d i n termediates. The f i r s t l i t e r a t u r e report of asymmetric 3-addition t o an e n a n t i o m e r i c a l l y pure a,3-ethylenic s u l f o x i d e appeared i n 1971 and i n v o l v e d 3-addition o f p i p e r i d i n e to propenyl s u l f o x i d e X (eq. 1) (6). The absolute stereochemistry of t h i s r e a c t i o n was r a t i o n a l i z e d by S t i r l i n g i n terms of t r a n s i t i o n s t a t e l a i n which the n u c l e o p h i l e approached the 3-carbon atom on that s i d e of the double bond remote from the bulky t o l y l group i n the conformation shown i n model ia. (§)·

9.

POSNER E T A L .

Vinylic

141

Sulfoxides

In 1973 Tsuchihashi reported asymmetric i n d u c t i o n during carbon-carbon bond formation between n u c l e o p h i l i c malonate and e l e c t r o p h i l i c e n a n t i o m e r i c a l l y pure s t y r y l s u l f o x i d e 2, producing intermediate diastereomeric carbanions 3 â and 3fc (eq 2) ( 7 ) . S e l e c t i v e formation of diastereomer 2 â * t h i s i r r e v e r s i b l e , k i n e t i c a l l y c o n t r o l l e d a d d i t i o n was r a t i o n a l i z e d i n terms of the preference f o r an o t - s u l f i n y l carbanion to have the carbon l o n e p a i r o r b i t a l trans to the s u l f i n y l oxygen o r b i t a l i n a p o l a r s o l vent. Asymmetric Reactions and Processes in Chemistry Downloaded from pubs.acs.org by COLUMBIA UNIV on 01/22/18. For personal use only.

η

Pursuing these two r e p o r t s as w e l l as our own i n t e r e s t i n organometallic a d d i t i o n s to unsaturated s u l f u r compounds, (8) we examined the behavior of some 1-alkenyl a r y l s u l f o x i d e s toward r e l a t i v e l y non-basic organocopper reagents with the aim of a t t a c h i n g a hydrocarbon group β to the s u l f u r atom i n a s t e r e o c o n t r o l l e d f a s h i o n . To our s u r p r i s e , r a t h e r than a d d i t i o n to the carbon-carbon double bond, m e t a l a t i o n occurred r e g i o s p e c i f i c a l l y at the 1 - p o s i t i o n generating a v i n y l m e t a l l i c s p e c i e s ; l i k e w i s e , m e t h y l l i t h i u m and s e v e r a l l i t h i u m amides produced such v i n y l m e t a l l i c species which reacted s u c c e s s f u l l y with a v a r i e t y of e l e c t r o p h i l e s to give v a r i o u s 1-substituted 1-alkenyl s u l f o x i d e s (e.g., eq 3) (9).

ASYMMETRIC

142

REACTIONS

AND

PROCESSES

IN

CHEMISTRY

Ph \

=0

1. Me CuU 2


2. Mel

η-Hex

Me 90%

Using e n a n t i o m e r i c a l l y pure 1-alkenyl a r y l s u l f o x i d e s ( E ) (+)-£ and (Z)-(-)-£, we found that 1-deprotonation and then r e p r o t o n a t i o n of the (E)-(+)-4 isomer produced no double bond i s o m e r i z a t i o n and no racemization, whereas s i m i l a r treatment of the ( Z ) (")"Ô isomer produced double bond i s o m e r i z a t i o n and some racemizat i o n (eqs. 4,5) (5a).

1. MeLi 2. H*

(§H+M

n-Non

(4)

Ca3 +95.2

(E)-(+)-*_ CCQ +95.7

C

D

D

. Ph

n-Non

'V

s = o

H ( Ζ ) - Η - Λ Ca: -200° D

1. MeLi 2. H

+

(E)-(+)-4 (5) 03^+67.3

9.

POSNER

ET AL.

Vinylic

Sulfoxides

143

Carboxylation of such a 1 - l i t h i o 1-alkenyl s u l f o x i d e l e d to a d i a s t e r e o m e r i c a l l y and e n a n t i o m e r i c a l l y pure ot-carboxyl α,βe t h y l e n i c s u l f o x i d e such as 5 â a f t e r p r o t o n a t i o n of the intermediate l i t h i u m c a r b o x y l a t e and t o the corresponding methyl e s t e r 5fe a f t e r methylation with methyl iodide-hexamethylphosphoramide (HMPA) (eq. 6) (5a).


(S

)-( )-5a,R=H. )%% +

Ph

Ph £=0 D-Hex

2)C0

2

=( n-HeX Mel HMPA

?=0

(6)

C00R

(§)-(+)-5b,R = Me,80% We reasoned that metal i o n complexation with α-carboxyl α,βe t h y l e n i c s u l f o x i d e s such as 5a and 5b should produce a c h e l a t e such as 6, l o c k i n g the s u l f o x i d e group i n t o the conformation shown. Approach of a n u c l e o p h i l i c m e t h y l m e t a l l i c species toward the 3-carbon atom should now occur from the unshielded s i d e of the carbon-carbon double bond and should lead t h e r e f o r e to (R)-3methylalkanoates with h i g h asymmetric i n d u c t i o n . Working model 6 f u r t h e r suggested that aromatic groups b u l k i e r than phenyl and metal ions that form strong complexes might p o s s i b l y lead to com p l e t e asymmetric i n d u c t i o n .

ASYMMETRIC


144

REACTIONS

AND

PROCESSES

IN

CHEMISTRY

a-Carboxyl α,β-ethylenic s u l f o x i d e §a, reacted with dimethylcoppermagnesium i o d i d e i n a conjugate manner; sodium amalgam r e d u c t i v e cleavage of the intermediate α-sulfinyl c a r b o x y l i c a c i d produced (R)-(+)-3-methylnonanoic a c i d i n 61% enantiomeric excess (eq. 7). Likewise, ot-methoxycarbonyl α,β-ethylenic s u l f o x i d e Sh reacted with dimethylcopperlithium followed by r e d u c t i v e s u l f u r carbon bond cleavage and s a p o n i f i c a t i o n to produce (R)-(+)-3methylnonanoic a c i d i n 65% enantiomeric p u r i t y (eq. 8, 53% over a l l y i e l d ) . Reversing the order of i n t r o d u c i n g the l a r g e r and the smaller a l k y l groups at the p r o c h i r a l 3-carbon atom a f f o r d e d mainly that enantiomer having opposite absolute stereochemistry. Thus ( E ) - l - p r o p e n y l s u l f o x i d e ( + ) ~ Z reacted with di-n-butylcopperl i t h i u m and then underwent r e d u c t i v e c a r b o n - s u l f u r bond cleavage and s a p o n i f i c a t i o n to form (S)-(-)-3-methylheptanoic a c i d (§) i n 59% enantiomeric p u r i t y (eq. 9) (5a). Higher asymmetric induc t i o n s , however, have been achieved r e c e n t l y by Meyers, by Mukaiyama and by Koga i n s y n t h e s i s of 3-methylalkanoic a c i d s W.

5a

(R)-(+) —


9.

POSNER

ET

AL.

Vinylic

Sulfoxides

145

In sharp c o n t r a s t to these h i g h l y s u c c e s s f u l methods f o r e n a n t i o s e l e c t i v e synthesis of some a c y c l i c systems, v i r t u a l l y no general method has been reported f o r e n a n t i o - c o n t r o l l e d preparat i o n of c y c l i c compounds. Because so many o p t i c a l l y pure carboc y c l e s are found i n nature and are important s y n t h e t i c i n t e r mediates, the need f o r e f f e c t i v e and h i g h l y asymmetric syntheses of such compounds i s obvious. More s p e c i f i c a l l y , although many e n a n t i o m e r i c a l l y pure n a t u r a l l y - o c c u r r i n g 3 - a l k y l c a r b o c y c l e s with small 3 - a l k y l groups are known, asymmetric synthesis of these compounds v i a attachment of the small a l k y l group i s u s u a l l y an extremely d i f f i c u l t process. Despite attempts at asymmetric induct i o n during organometallic conjugate a d d i t i o n to 2-cycloalkenones using o p t i c a l l y a c t i v e solvents (10) or o p t i c a l l y a c t i v e l i g a n d s , (11) only poor e n a n t i o s e l e c t i v i t y has been achieved. We reasoned that some c y c l i c enone s u l f o x i d e s should form an even more r i g i d chelate than that formed from the corresponding a c y c l i c a l k e n y l s u l f o x i d e s when complexed with metal i o n s ; model § exemplifies the case f o r a eyelopentenone s u l f o x i d e and suggests a high degree of s t e r e o c o n t r o l during the n u c l e o p h i l i c a d d i t i o n reaction.

Cyclopentenone s u l f o x i d e (S)-(+)~lfi was prepared v i a eq. 10 i n good y i e l d on a few mg as w e l l as on a 10-gm s c a l e (5a). This enone s u l f o x i d e , which i s c r y s t a l l i n e and s t a b l e at l e a s t f o r s e v e r a l months, reacted with methylmagneslum i o d i d e [ i n the absence of copper (I)] i n a conjugate manner; aluminum amalgam carbon-sulfur bond r e d u c t i v e cleavage produced (R) - (+)-3-methylcyclopentanone (U) i n 71% chemical y i e l d and i n 80% enantiomeric p u r i t y (eq. 11). The absolute stereochemistry of t h i s asymmetric i n d u c t i o n i s c o n s i s t e n t with working model 9 and approach of the methyl n u c l e o p h i l e from the pro-(R) d i r e c t i o n . Likewise, d i methylcopperlithium reacted with cyclopentenone s u l f o x i d e (§)-(+)Ifi to g i v e , a f t e r r e d u c t i v e s u l f u r - c a r b o n bond cleavage, (R)-(+)-

146

ASYMMETRIC

3-methylcyclopentanone meric p u r i t y .

REACTIONS

A N D PROCESSES I N CHEMISTRY

(JJ.) i n 91% chemical y i e l d and 80% enantio

Toi Br |


1

=

\ /

1 ) B r Q

2^

2)EtgN

Γ^ι I

DHOCHgCHgOH (10)

/

°2)n-BuLi

*

3) (-)-TolSOMenthyl

4) C u S 0

4 >

I acetone

mp

121-122"

ta]J (

c

0

Λ

2

1

+ >

141.7° one)

a c e t

(S)-(+)-10

Me 11

(S)-(+)-10

MeMgl

% Yield

% e.e.

77

80 (11)

Me CuLi 2

(S)-(+)-10

Al/Hg

91

80

To preform a strong enone s u l f o x i d e - m e t a l i o n complex and thus p o s s i b l y t o i n c r e a s e the amount o f asymmetric i n d u c t i o n , s e v e r a l metal dibromides were added t o cyclopentenone s u l f o x i d e (S)-(+)-10. As shown i n eq. 12, only z i n c dibromide was h i g h l y e f f e c t i v e i n r a i s i n g the extent o f asymmetric i n d u c t i o n during methyl Grignard conjugate a d d i t i o n .

POSNER

9.

»

M

ET

Br P


(s)-io

Vinylic

AL.

^

147

Sulfoxides

Me \

MeMgX^ Al-Hg

2

^ (12) % Yield 96e.e.

Ni Co Pd Mg Zn

Br Br Br I

53 73 58 81

70 70 71 73

I

99

87

The best stereochemical r e s u l t s , however, were obtained with the new and bulky m e t h y l m e t a l l i c reagent, methyl t r i i s o p r o p o x y t i t a n i u m , (12) and with methylmagnesium c h l o r i d e (eq. 13). Pre sumably, the more e l e c t r o p h i l i c chloromagnesium s p e c i e s formed a stronger complex with the bidendate enone s u l f o x i d e than d i d the bromo or the iodomagnesium species (13) and thus forced the β a d d i t i o n to proceed e n t i r e l y through the chelated and t h e r e f o r e locked conformation shown i n model 9.

=\

Me-M % Yield %e,e. MeTi(0Pr-i)

3

MeMgCl

American Chemical Society Library 16th st. N. nr. WttMogton, 0. C. 2009· 1155

90

90

91

95-100

148

ASYMMETRIC

REACTIONS

AND

PROCESSES

IN

CHEMISTRY


We have a l s o prepared (R)-(+)-3-methylcyclohexanone (13) v i a m e t h y l m e t a l l i c conjugate a d d i t i o n to e n a n t i o m e r i c a l l y pure c y c l o hexenone s u l f o x i d e (S)-(+)-12 (eq. 14). Equations 13 and 14 represent h i g h l y s u c c e s s f u l asymmetric syntheses of 3-methylcyclopentanone and 3-methylcyclohexanone and i l l u s t r a t e a general new method f o r p r e p a r a t i o n of 3 - a l k y l c a r bocycles of h i g h or v i r t u a l l y complete enantiomeric p u r i t y (14).

(CH ) CuLi 3

2

AL-H

>

(SM+H2

90% /ield 72% e.e. 1. ZnBr

AHHg^

2

2. CH M Br 3

g

ioo % Yield 83% e.e.

Besides conjugate a d d i t i o n of the small methyl group, c y c l o pentenone s u l f o x i d e (S)-(+)-lû a l s o underwent conjugate a d d i t i o n of a l a r g e naphthyl group. As shown i n scheme I , we have a p p l i e d t h i s r e a c t i o n which proceeds with complete asymmetric i n d u c t i o n to e f f i c i e n t c o n s t r u c t i o n of 3-naphthylcyclopentanone 1£ having the n a t u r a l absolute s t e r o i d c o n f i g u r a t i o n at carbon 14 ( s t e r o i d numbering). Reductive cleavage of the s u l f i n y l group using dimethylcopperlithium allowed r e g i o s p e c i f i c formation of enolate i o n 15 which underwent carbon a l k y l a t i o n to g i v e only 9,11-seco s t e r o i d 1É having the d e s i r e d 13S-14J5 absolute stereochemistry! Synthetic seco s t e r o i d 16 was i d e n t i c a l by HPLC, NMR, IR, mass spectrometry, m e l t i n g point (116.5-118°C), mixed m e l t i n g p o i n t and o p t i c a l r o t a t i o n [ [ a ] ^ 5 = +168° (ς 0.36, CHCl3)]to a sample of 16 prepared by degradation of n a t u r a l e s t r a d i o l (5a). Because we have p r e v i o u s l y converted racemic 16 i n t o the racemic s t e r o i d e q u i l e n i n 17, (15) p r e p a r a t i o n of e n a n t i o m e r i c a l l y pure 1$ amounts to a formal t o t a l s y n t h e s i s of e n a n t i o m e r i c a l l y pure e q u i l e n i n 12. 3-Vinylcyclopentanone lg and the corresponding enol s i l y l ether 12 have been used r e c e n t l y i n some elegant, c r e a t i v e , and e f f i c i e n t c o n s t r u c t i o n s of estrones v i a i n t r a m o l e c u l a r D i e l s A l d e r c y c l o a d d i t i o n r e a c t i o n s of intermediate O-quinodimethanes (Scheme II) (16-18). Only one r e p o r t , however, has appeared t

0


9. POSNER ET AL.

>98 %

Vinylic Sulfoxides

16, 8 9 %

e.e.

Scheme L

149

17

Scheme

IL



9.

POSNER

ET

AL.

Vinylic

Sulfoxides

151

i n v o l v i n g asymmetric s y n t h e s i s of o p t i c a l l y a c t i v e s t e r o i d i n t e r mediate 18 used i n p r e p a r a t i o n of o p t i c a l l y a c t i v e estrones v i a g e n e r a l i z e d scheme I I ( 1 6 i ) . We found that e n a n t i o m e r i c a l l y pure cyclopentenone s u l f o x i d e (S)-(+)~lû reacted with vinylmagnesium bromide i n the presence of a c a t a l y t i c amount of cuprous bromide and then with methyl i o d i d e to g i v e 2 , 2 , 3 - t r i s u b s t i t u t e d cyclopentanone 20 (Scheme I I I ) . T r i s u b s t i t u t e d cyclopentanone 20, however, could be formed i n b e t t e r y i e l d (^75%) v i a the corresponding sodio enolate. Aluminum amalgam r e d u c t i v e cleavage produced 3-vinylcyclopentanone (S)-l§ i n 80% enantiomeric p u r i t y . The amount of asymmetric i n d u c t i o n was improved d r a m a t i c a l l y , however, by f i r s t complexing cyclopentenone s u l f o x i d e (S)-10 with z i n c dibromide and then adding v i n y l magnesium bromide. In t h i s way, f o l l o w i n g scheme I I I , 3 - v i n y l cyclopentanone (S)-18 was formed i n >98% enantiomeric p u r i t y and i n 55-60% o v e r a l T y i e l d ! Reductive cleavage of α-sulfinylcyclopentanone 2g using dimethylcopperlithium followed by a d d i t i o n of t r i m e t h y l s i l y l c h l o r i d e gave e n a n t i o m e r i c a l l y pure enol s i l y l ether (S)-(+)-19 i n 54% o v e r a l l y i e l d (5b). T h i s complete asym metric i n d u c t i o n i n s y n t h e s i s of s t e r o i d intermediates (S)-18 and and (S)-19 amounts to a formal t o t a l s y n t h e s i s of e n a n t i o m e r i c a l l y pure estrone! I t i s c l e a r from the r e s u l t s summarized here that some very s u c c e s s f u l , general, and h i g h l y u s e f u l asymmetric syntheses of carbon-carbon bonds can be performed u s i n g e n a n t i o m e r i c a l l y pure 1-carbonyl 1-alkenyl s u l f o x i d e s and v a r i o u s organometallic r e agents. These r e s u l t s add s i g n i f i c a n t l y to the r a p i d l y growing number of new, r a t i o n a l l y designed, and h i g h l y s t e r e o c o n t r o l l e d C-C bond-forming s y n t h e t i c methods and should be e s p e c i a l l y use f u l i n asymmetric s y n t h e s i s of e n a n t i o m e r i c a l l y pure 3-substituted carbocycles.


152 ASYMMETRIC

1)

Scheme

REACTIONS

III.

AND PROCESSES IN

Si Me

(SH8

(S)-(+)-l9

CHEMISTRY

Toi

(§)-(+)-! 0 ZnBr-

2)

1)

N^CuLi

2)

CI Si M e ,

:

9.

POSNER E TA L .

Vinylic

Sulfoxides

153

Acknowled gement


We g r a t e f u l l y acknowledge f i n a n c i a l support from the N a t i o n a l Science Foundation (CHE 79-15161), from the Donors o f the P e t r o leum Research Fund, administered by the American Chemical S o c i e t y , from G. D. Searle and Co., and from Merck, Sharp, and Dohme. We warmly acknowledge experimental help from P-W. Tang and A. Y. Black.

Literature Cited 1.

2.

3. 4.

5.

6. 7. 8. 9. 10. 11.

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12. (a) Weidmann, B.; Wildler, L . ; Olivero, A.G.; Maycock, C.D.; Seebach, D. Helv. Chim. Acta 1981, 64, 357. (b) Reetz, M.T.; Steinbach, R.; Westermann, J.; Peter, R. Angew. Chem. Inst. Ed. Engl. 1980, 19, 1011. 13. Ashby, E.C.; Laemmle, J.; Newmann, H.M. Accts. Chem. Res. 1974, 7, 272, and references therein. 14. For a recent synthetic approach to optically active 3-alkylated cyclopentanones and cyclohexanones, see Taber, D.F.; Saleh, S.A.; Korsmeyer, T.W. J. Org. Chem. 1980, 45, 4699. 15. Posner, G.H.; Chapdelaine, M.J.; Lentz, C.M. J. Org. Chem. 1979, 44, 3661. 16. (a) Oppolzer, W.; Petrzilka, M.; Battig, K. Helv. Chim. Acta 1977, 60, 2965. (b) Kametani, T.; Nemoto, H.; Fukumoto, K. J. Amer. Chem. Soc. 1977, 99, 3461. (c) Funk, R.L; Vollhardt, K.P.C. J. Amer. Chem. Soc. 1977, 99, 5483 and 1979, 101, 215. (d) Oppolzer, W.; Battig, K.; Petrzilka, M. Helv. Chim. Acta 1978, 61, 1945. (e) Nicolaou, K.C.; Barnette, W.E.; Ma, P. J. Org. Chem. 1980, 45, 1463. (f) Djuric, S.; Sarkan, T.; Magnus, P. J. Amer. Chem. Soc. 1980, 102, 6885. (g) Ito, Y.; Nakatsuka, M.; Saegusa, T. J. Amer. Chem. Soc. 1981, 103, 476. (h) Quinkert, G.; Weber, W-D.; Schwartz, U.; Durner, G. Angew. Chem. Int. Ed. Engl. 1980, 19, 1027. (i) Quinkert, G.; Schwartz, U.; Stark, H.; Weber, W-D.; Baier, H.; Adam, F.; Durner, G. Angew. Chem. Int. Ed. Engl. 1980, 19, 1029. 17. For a review, see Oppolzer, W. Synthesis 1978, 793. 18. A resolved cyclopentanone acetic acid has been used in syn thesis of two optically pure estrone derivatives: Oppolzer, W.; Roberts, D.A. Helv. Chim. Acta 1980, 63, 1703. RECEIVED December 14, 1981.

Asymmetric Reactions and Processes in Chemistry - American

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