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Synthetic Communications: AnInternational Journal for RapidCommunication of SyntheticOrganic ChemistryPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lsyc20

Regioselective Synthesis of 2-Functionalized Thiophenes byCondensation of α-MercaptoCompounds with β-AminoenoneDerivativesAngel Alberola a , José M. Andrés a , AlfonsoGonzãlez a , Rafael Pedrosa a & Pedro Prãdanos aa Departamento de Quimica Orgãnica. Facultadde Ciencias , Universidad de Valladolid , 47011,Valladolid, SpainPublished online: 24 Oct 2006.

To cite this article: Angel Alberola , José M. Andrés , Alfonso Gonzãlez , RafaelPedrosa & Pedro Prãdanos (1990) Regioselective Synthesis of 2-FunctionalizedThiophenes by Condensation of α-Mercapto Compounds with β-AminoenoneDerivatives, Synthetic Communications: An International Journal for RapidCommunication of Synthetic Organic Chemistry, 20:16, 2537-2547, DOI:10.1080/00397919008053203

To link to this article: http://dx.doi.org/10.1080/00397919008053203

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SYNTHETIC COMMUNICATIONS, 20(16), 2537-2547 (1990)

R E G I O S E L E C T I V E S Y N T H E S I S OF 2 - F U N C T I O N A L I Z E D

T H I O P H E N E S BY CONDENSATION OF d-MERCAPTO COMPOUNDS

W I T H P-AMINOENONE D E R I V A T I V E S

A n g e l A l b e r o l a * , J o s e M . A n d r e s , A l f o n s o G o n z h l e z ,

R a f a e l P e d r o s a , P e d r o P r a d a n o s .

D e p a r t a i n e n t o de Q u i m i c a O r g b n i c a . F a c u l t a d de C i e n c i a s .

U n i v e r s i d a a de V a l l a d o l i d , 4 7 0 1 1 - V a l l a d o l i d , S p a i n .

Abstract. 2 - A c y l t h i o p h e n e s a n d e t h y l Z - t h i o p h e n e -

c a r b o x y l a t e s a r e p r e p a r e d r e g i o s e l e c t i v e l y b y r e a c t i o n

o f 3 - c h l o r o e n o n e s a n d 2 - a c y l e n a m m o n i u m c h l o r i d e s w i t h

N - m e r c a p t o d e r i v a t i v e s i n g o o d t o m o d e r a t e y i e l d s .

The u s e o f 1 , 3 - D i f u n c t i o n a l s u b s t r a t e s i n t h e

s y n t h e s i s o f t h i o p h e n e d e r i v a t i v e s h a s b e e n d e s c r i b e d

some y e a r s a g o . 1 - 3 To t h i s e n d , 0 - m e r c a p t o c r o t o n i c

e s t e r s , p - m e r c a p t o t h i o a c r y l a t e s , a n d r n e r c a p t o m a l o n i c

e s t e r s ' h a v e b e e n c y c l i z e d t o t h i o p h e n e d e r i v a t i v e s

f o l l o w i n g a D i e c k m a n - t y p e c o n d e n s a t i o n . M o r e r e c e n t l y ,

t h e r e a c t i o n o f m e t h y l t h i o g l y c o l a t e w i t h a c e t y l e n e

d i c a r b o x y l a t e s , 7 e t h y l a c e t o a c e t a t e , 8 y 9 P - d i k e t o n e s ,

t h e i r e n o l s and a l k o x y m e t h y l e n e k e t o n e s h a s b e e n

* To whom c o r r e s p o n d e n c e s h o u l d b e a d r e s s e d

253 7

Copyright 0 1990 by Marcel Drkker, Inc.

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2538 ALBEROLA ET AL.

exploited in the preparation o f 3-hydroxythiophenes, whereas thioglycolic acid and its esters react with 1 - c h l o r o p r o p e n - 3 - y l i d e n e immonium salts, l 3 3-chloro- acrol ei n s y 1 and 3-chl oroenones l 4 leading to 2-thiophenecarboxylic acid derivatives.

On the other hand, we have recently reported the 16 regioselective synthesis o f 2- and 3-acylpyrroles,

2 ( 1 H)pyridones' and pyrazol es18 from p-ami noenones and now we have extended our work to the preparation of 2-functionalized thiophenes.

Attempts to prepare thiophene derivatives by reaction o f 4 - p y r r o l i d i n y l - 3 - p e n t e n - 2 - o n e and 4-amino- 3-penten-2-one with ethyl thioglycolate or d-mercapto- acetone in both basic (sodium ethoxide in ethanol or triethylamine i n benzene) or thermally [ D M F , reflux) induced conditions were unsuccessful giving a very complex mixture of products. This was circumvented by starting from 3-substituted enones with a better leaving group, such as 3-chloroenones 1A-6 or acylenammonium chlorides E.

R1& + NaSCI-$CO2Et EtOH, 78'C

0 CI 0 SCHZC02Et 1 2 3

I R~ ~ C O * ~t

4

Scheme 1

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REGIOSELECTIVE SYNTHESIS OF THIOPHENES 2539

I n f a c t , 3 - c h l o r o e n o n e s r e a c t w i t h t h e s o d i u m s a l t

o f e t h y l t h i o g l y c o l a t e t o p r o v i d e i n e x c e l l e n t y i e l d s ,

t h e s u b s t i t u t i o n p r o d u c t s 3 f o r c o m p o u n d s ~ 1A-C o r t h e

e t h y l t h i o p h e n e c a r b o x y l a t e s 40a-Ga f r o m c o m p o u n d s l D - G ( S c h e m e 1 a n d T a b l e 1 ) . On t h e c o n t r a r y , t h e

p r o c e d u r e f a i l s when t h e s t a r t i n g c o m p o u n d s a r e

c t - m e r c a p t o k e t o n e s b e c a u s e t h e i r s o d i u m s a l t s a r e n o t

s t a b l e e n o u g h i n t h e r e a c t i o n c o n d i t i o n s .

-

On t h e o t h e r h a n d , a c y l e n a m m o n i u m c h l o r i d e s

5A-C,H,I a r e e a s i l y t r a n s f o r m e d , i n h i g h y i e l d s , i n t o

t h e i n t e r m e d i a t e s 3 when r e f l u x e d i n e t h a n o l f o r 1 o r 2

h w i t h d - m e r c a p t o d e r i v a t i v e s __ 2 a - c . The t r a n s f o r m a t i o n

o f t h e s e i n t e r m e d i a t e s i n t o 2 - f u n c t i o n a l i z e d t h i o p h e n e s

i s c a r r i e d o u t , i n g o o d t o m o d e r a t e y i e l d s , b y

c y c l i z a t i o n w i t h s o d i u m e t h o x i d e i n e t h a n o l a t r e f l u x

o r room t e r n p e r a t u r e ( S c h e r n e 2 a n d T a b l e 2 ) .

We h a v e p r e v i o u s l y d e s c r i b e d t h e c y c l i z a t i o n o f t h e

N - a c y l i n t e r m e d i a t e s h o m o l o g o u s o f - 3 as a r e g i o -

s e l e c t i v e p r o c e s s l e a d i n g t o m i x t u r e s o f 2 - a n d / o r

3 - a c y l p y r r o l e s d e p e n d i n g on t h e n a t u r e o f t h e

s u b s t i t u e n t s a t t h e c a r b o n y l m o i e t i e s . 1 6 N e v e r t h e l e s s ,

T a b l e 1 . R e a c t i o n o f ( 3 - c h l o r o e n o n e s 1A-6 w i t h the s o d i u m s a l t o f e t h y l t h i o g l y c o l a t e .

Compd. R ’ R * R3 P r o d u c t ( % )

1 A E t H H 3 A a ( 8 5 )

1 B 4-MeOC6H4 H H 3 B a ( 7 6 1

1c 4 -02NC6H4 H H 3 C a ( 8 0 )

1 D Me H Me 4 D a ( 50 1 1 E Me Me Me 4Ea ( 5 7 )

1 F P h H Me 4 F a ( 6 7 )

16 Me H Ph 4 G a ( 7 0 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2540 ALBEROLA ET AL.

5 2 3

R ' R 2

5A E t 2a O E t 5B 4-MeOC6H4 2b M e 5C 4-02NC6H4 2c P h 5H i - P r 51 P h

1 EtONaI EtOH

T2 "2

4

S c h e m e 2

T a b l e 2. R e a c t i o n o f 5A-C,H,I w i t h # -mercap to

d e r i v a t i v e s

5 5A

5A

5A 56

5B

5c 5c

5H

5H 5 1 5 1

- - 2 t , ( H ) 2 a 1 2b 1

2c 2

2a 2 2b 1 2a 2

2b 1

2a 1

2b 1 2a 2

2b 1

- 3 ( % ) T 2 ( OC) t 2 ( H 1 - 4(%1a 3Aa( 8 2 ) 78 2 4Aa( 45 1 3Ab(761 2 0 2 4Ab( 2 8 )

3Ac(931 20 2 4Ac ( 3 3 1 3Ba

3Bb

3Ca

3Cb

3Ha

74 1 78 2 4Ba( 3 2 )

87 1 2 0 3 4Bb( 2 7 1 83 1 78 1 . 5 4Ca( 45 1 80 1 20 1 4Cb(401

85 1 78 2 4Ha( 3 0 1 3Hb( 80 1 20 2 4Hbt231

3 1 a ( 9 1 1 78 2 4 I a ( 5 1 1 3 I b ( 7 0 ) 20 1 4 I b ( 4 9 1

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REGIOSELECTIVE SYNTHESIS OF THIOPHENES 2541

i n t h e p r e s e n t c a s e t h e c y c l i z a t i o n s t e p o f t h e

i n t e r m e d i a t e s - 3 i s a r e g i o s p e c i f i c t r a n s f o r m a t i o n i n t o

2 - f u n c t i o n a l i z e d t h i o p h e n e s , a n d may b e e x p l a i n e d as a

c o n s e q u e n c e o f t h e a b i l i t y o f t h e s u l f u r t o s t a b i l i z e

t h e n e g a t i v e c h a r g e i n t h e r e a c t i v e c a r b a n i o n .

The d e s c r i b e d m e t h o d c o n s t i t u t e s a t w o - s t e p ,

o n e - p o t p r o c e d u r e t h a t a1 l o w s t h e p r e p a r a t i o n o f

2 - t h i o p h e n e c a r b o x y l a t e s , a n d t h e l e s s a c c e s s i b l e

2 - a c y l t h i o p n e n e d e r i v a t i v e s s t a r t i n g f r o m a common

s u b s t r a t e 5 . -

E x o e r i m e n t a l

M p ' s a r e u n c o r r e c t e d a n d w e r e d e t e r m i n e d on an o p e n

c a p i l l a r y t u b e . N M R w e r e r e g i s t e r e d on a B r u k e r AC80 a t

80 MHz, a n d c h e m i c a l s h i f t s a r e g i v e n i n ppm d o w n f i e l d

f r o m TMS u s e d as i n t e r n a l s t a n d a r d . Mass s p e c t r a w e r e

m e a s u r e d on a H e w l e t t - P a c k a r d 5988A mass s p e c t r o m e t e r

b y e l e c t r o n i c i m p a c t a t 7 0 e V . 3 - C h l o r o v i n y l -

k e t o n e s , 19 - ' ' 2 - a c y l enammonium c h l o r i d e s , 2 2 N - m e r c a p t o -

a c e t o n e , 2 3 a n d M - m e r c a p t o a c e t o p h e n o n e 2 4 y 2 5 w e r e s y n t h e -

s i z e d as p r e v i o u s l y d e s c r i b e d .

R e a c t i o n o f 3 - c h l o r o v i n y l k e t o n e s w i t h t h e sodium s a l t

o f e t h y l t h i o g l y c o l a t e . Genera l p r o c e d u r e . A s o l u t i o n

o f t h e 3 - c h l o r o v i n y l k e t o n e - 1A-G ( 1 0 m m o l ) a n d t h e

s o d i u m s a l t o f e t h y l t h i o g l y c o l a t e ( l . 5 6 g , 1 1 m m o l ) w a s

r e f l u x e d i n a n h y d r o u s e t h a n o l ( 2 5 mL) u n t i l t h e

r e a c t i o n was f i n i s h e d ( t l c ) . The r e a c t i o n m i x t u r e was

c o o l e d t o R T a n d t h e e t h a n o l was r e m o v e d u n d e r v a c u u m .

The r e s i d u e was r e d i s s o l v e d i n a n h y d r o u s THF, t h e

s o l i d s w e r e f i l t e r e d o f f and t h e s o l v e n t was e l i m i n a t e d

( R o t a v a p o r ) . T h e o i l y r e s i d u e s t i n t e r m e d i a t e s 3Aa-3Ca f r o m - 1A-C o r e t h y l 2 - t h i o p h e n e c a r b o x y l a t e s f r o m 1D-6 )

w e r e p u r i f i e d b y f l a s h c h r o m a t o g r a p h y on s i l i c a g e l a n d t o l u e n e a s s o l v e n t .

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25h2 ALBEROLA ET AL.

R e a c t i o n o f 2-acylenammonium c h l o r i d e s 5 A - C y H y I w i t h

o(-mercapto d e r i v a t i v e s 2 a - c . G e n e r a l p r o c e d u r e . A

m i x t u r e o f t h e compound - 5 ( 1 0 m m o l ) and t h e

c o r r e s p o n d i n g a - m e r c a p t o d e r i v a t i v e - 2a-c ( 1 1 m m o l ) i n

a n h y d r o u s e t h a n o l ( 2 5 mL) was r e f l u x e d f o r t h e t i m e

g i v e n i n T a b l e 2 a s t l . The s o l u t i o n was c o o l e d a t R T ,

t h e e t h a n o l was e v a p o r a t e d ( R o t a v a p o r ) a n d t h e r e s i d u e

was t a k e n u p i n a n h y d r o u s T i l F ( 2 0 mL). The s o l i d was

f i l t e r e d , t h e THF e l i m i n a t e d u n d e r vacuum and t h e o i l y

r e s i d u e was r e d i s s o l v e d i n a n h y d r o u s e t h a n o l ( l 0 n i L ) . To t h i s s o l u t i o n was d r o p p e d , u n d e r n i t r o g e n , a s o l u t i o n

o f s o d i u m e t h o x i d e ( 0 . 6 8 g , 1 0 m m o l ) i n a n h y d r o u s

e t h a n o l ( l 0 m L ) , a n d t h e m i x t u r e was s t i r r e d a t K T o r

r e f l u x f o r t h e t i m e i n d i c a t e d i n T a b l e 2 as t 2 . The

r e a c t i o n was q u e n c h e d w i t h c o n c e n t r a t e d HC1 ( 3 m L ) a n d

c r u s h e d i c e ( l 0 g ) , a n d e x t r a c t e d w i t h d i e t h y l e t h e r -

( 2 x 2 5 m L ) . The o r g a n i c l a y e r was d e c a n t e d , w a s h e d w i t h

b r i n e a n d w a t e r a n d d r i e d o v e r a n h y d r o u s MgS04. The

s o l v e n t was e l i m i n a t e d u n d e r vacuum a n d t h e r e s i d u e was

p u r i f i e d b y f l a s h c h r o m a t o g r a p h y on s i l i c a g e l u s i n g

t o l u e n e as e l u a n t .

I n t h e f o l l o w i n g p a r a g r a p h s a r e g i v e n t h e p h y s i c a l

a n d s p e c t r o s c o p i c p r o p e r t i e s o f t h e 2 - f u n c t i o a n a l i z e d

t h i o p h e n e s o b t a i n e d .

E t h y l 3 - E t h y l - 2 - t h i o p h e n e c a r b o x y l a t e ( 4 A a ) . C o l o u r l e s s

l i q u i d . B p . 1 1 6 - 1 1 9 ~ C / 2 0 t o r r . NMR(CC14) : 1 . 2 0 ( t , J = 7

H z , 3 H ) ; 1 . 3 0 ( t , J - 7 H z , 3 H ) ; 3 . 0 3 ( q , J = 7 H z , 2 H ) ;

4 . 3 0 ( q , J = 7 H z , 2 H ) ; 6 . 9 5 ( d , J = 5 H z , 1 H ) ; 7 . 3 8 ( d , J = 5

H z , l H ) . M S , m/z(%): 1 8 4 ( M f , 5 1 ) ; 1 7 9 ( 1 0 0 1 . H y d r o l y s e d b y

s t i r r i n g w i t h a 6 N s o l u t i o n o f K O H t o

3 - E t h y l - 2 - t h i o p h e n e c a r b o x y l i c a c i d . Mp. 1 l 0 - 1 l l e C ( f r o m

H 2 0 ) . C,H802S r e q u i r e s : C , 5 3 . 8 3 ; H , 5 . 1 6 . F o u n d : C ,

5 3 . 9 6 ; H, 5 . 2 7 .

2-Acetyl-3-ethylthiophene ( 4 A b ) . C o l o u r l e s s l i q u i d . Bp .

1 0 2 - 1 0 5 9 C / 1 0 t o r r ( l i t . , 2 ’ 2 2 7 ’ C / 7 6 0 t o r r ) . NMR(CC14):

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REGIOSELECTIVE SYNTHESIS OF THIOPHENES 2 5 4 3

1.20(t,J=7 Hz, 3H); 2.45(s, 3H); 3.03(q,J=7 Hz, 2H); 7.03(d,J=5 Hz, 1H); 7.40(d,J=5 Hz, 1H). M S , m/z(%): 1 5 4 (M+, 52 1 ; 139 ( 100). 2 - B e n z o y l - 3 - e t h y l t h i o p h e n e (4Ac). Colourless oil. Bp. 135-138"C/2 torr. NMR(CC14): 1.17(t,J=7 Hz, 3H); 2.90 (q,J=7 Hz, 2H); 6.97(d,J=5 Hz, 1H); 7.20-8.00(m, 6H). MS, m/z ( % ) : 21 6(M+, 100). 2,4-Di ni trophenyl hydrozone, yellow solid, mp. 197-198eC(from EtOH). ClgHl6N4O4S requires: C , 57.57; H, 4.07; N , 14.13. Found: C, 57.71; H, 4.18; N , 14.21. E t h y l 3-(p-Methoxyphenyl~-2-thiophenecarboxylate (4Ba). Colourless solid. Mp. 46-47"C(from hexanes). NMR (CDC13): 1.18(t,J=7 Hz, 3H); 3.72(s, 3H); 4.18(q,J-7 Hz, 2H); 6.83(d,J=9 Hz, 2H); 6.98(d,J-5 Hz, 1 H ) ; 7.38(d,J=5 Hz, 1H); 7.40(d,J=9 Hz, 2H). MS, m / z ( % ) :

262(M+,100). C14H1403S requires: C, 64.10; H, 5.38. Found: C, 64.22; H, 5.27. 2-Acetyl-3-(p-rnethoxyphenyl)thiophene (4Bb). Colourless solid. Mp. 55-56'C(from hexanes). NMR(CDC13): 2.03(s, 3H); 3.78(s, 3H); 6.90(d,J=9 Hz, 2H); 6.95(d,J=5 Hz, 1H); 7.28(d,J=9 Hz, 2H); 7.45(d,J=5 Hz, 1H). MS,m/z(%): 232(M+,86); 217(100). C13H1202S requires: C, 67.22; H, 5.21. Found: C, 67.13; H, 5.33. E t h y l 3-(p-Nitrophenyl)-2-thiophenecarboxylate (4Ca). Yellow solid. Mp. 700-101eC(from hexanes). NMR(CDC13): 1.25(t,J=7 Hz, 3H); 4.22(q,J=7 Hi!, 2H); 7.05(d,J=5 Hz, 1H); 7.52(d,J=5 Hz, 1H); 7.57(d,J=8 Hz, 2H); 8.20(d, J = 8 Hz, 2H). MS, m/z(%): 277(M+,100). C 1 3 H l l N 0 4 S requires: C , 56.31; H, 4.00; N , 5.05. Found: C, 56.42; H, 3.91; N , 5.15. Z-Acety1-3-(p-nitrophenyl)thiophene (4Cb). Yellow solid Mp. 130-131eC(from EtOH). NMR(CDC13): 2.28(s, 3H); 7.17 (d,J=5 Hz, 1H); 7.66(d,J=8 Hz, 2H); 7.80(d,J=5 Hz, 1H); 8.25(d,J-8 Hz, 2H). MS, m / z ( % ) : 247(M+,68); 232(100).

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C H N03S requires: C , 58.29; H , 3.67; N , 5.66. Found: C, 58.17; H, 3.59; N , 5.76. E t h y l 3,5-Dimethyl-2-thiophenecarboxylate (4Da). Colour- less liquid. Bp. 47-5O2C/O.3 torr. NMR(CDC13): 1.30(t, J=7 Hz, 3H); 2.38(s, 3H); 2 . 4 3 ( ~ , 3H); 4.23(q,J=7 Hz, 2H); 6.53(broad s , 1H). M S , m l z ( % ) : 184(Mf,47); 139 ( 1 0 0 ) . Hydrolysed by stirring with a 6N solution o f KOH to 3 , 5 - D i m e t h y l - 2 - t h i o p h e n e c a r b o x y l i c acid. Mp. 170- 171'C (from EtOH-H20), (lit.,26 mp.171'C). E t h y l 3,4,5-Trimethyl-2-thiophenecarboxylate (4Ea). Colourless l i q u i d . Bp. 62-65'C/0.3 torr. . NMR(CDC13): 1.30(t,J=7 Hz, 3H); 1.97(~, 3H); 2 . 3 0 ( ~ , 3H); 2.38 ( s ,

3H); 4.23(q,J=7 Hz, 2H . MS, m/z(%): 198(M+,51); 153 (100). Hydrolysed by st rring with a 6N solution of KOH to 3,4,5-trimethyl-Z-th ophenecarboxylic acid. M p . 208- 209'C (from EtOH-H20),( it.,26 mp.209'C). E t h y l 5-Methyl-3-phenyl-2-thiophenecarboxylate (4Fa). Colourless solid. Mp. 82-83'C(from hexanes). NMR(CDC13) 1.15(t,J=7 Hz, 3H); 2.43(s, 3H); 4.10(q,J=7 Hz, 2 H ) ;

6.68(s, 1H); 7.10-7.50(m, 5H). MS, m/z(%): 246(M+,68); 201 (100). C14H1402S requires: C , 68.26; H, 5.73. Found: C, 68.38; H , 5.84. E t h y l 3-Methyl-5-phenyl-2-thiophenecarboxylate ( 4 G a ) .

Colourless solid. Mp. 46-47'C(from hexanes). NMR(CDC13) 1.33(t,J=7 Hz, 3H); 2.50's, 3H); 4.27(q,J=7 Hz, 2H); 7.00 ( s , 1H); 7.20-7.'O(m, 5H). MS, m/z(%): 246 (M+,100). C14H1402S requires: C, 68.26; H , 5.73. Found: C, 68.18; H, 5.86. E t h y l 3-isoPropyl-2-thiophenecarboxylate (4Ha). C o l o u r - less liquid. Bp. 84-85/10 torr. NMR(CDC13): 1.22(d,J=7 Hz, 6H); 1.30(t,J=7 Hz, 3H); 4.05(m,J=7 Hz, 1H); 4.30 ( q , J=7 Hz, 2H); 7.05(d,J=5 Hz, 1H); 7.37(d,J=5 Hz, 1H). M S , m/z(%): 198(Mt,43); 151(100). Hydrolysed by stirring with a 6N solution o f KOH to 3-isopropyl- __

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2-thiophene carboxylic acid. Mp. 108-1099C(from H20). C8H1002S requires: C, 56.45; H, 5.92. Found: C, 56.56; H , 6.03. 2 - A c e t y l - 3 - i s o p r o p y l t h i o p h e n e (4Hb). Colourless l i q u i d . Bp. 92-96/10 torr.NMR(CDC13): 1.18(d,J=7 Hz, 6H); 2.43 ( s , 3H); 4.00(m,J-7 Hz, 1H); 7.12(d,J=5 Hz, 1H); 7.38 ( d , J=5 Hz, 1H). MS, m/z(%): 168(M+,57); 119(100). Derivatized as 2,4-Dinitrophenylhydrazone. Yellow solid Mp. 163-164?C (from EtOH). C15H16N404S requires: C, 51 .72; H , 4.63; N , 16.08. Found: C, 51.59; H, 4.76; N , 15.99. Ethyl 3 - P h e n y l - 2 - t h i o p h e n e c a r b o x y l a t e ( 4 I a l . Colourless solid. Mp. 60-61QC(from hexanes), (1it.,l5 mp. 61.5'C). NMR(CDC13): 1.10(t,J=8 Hz, 3H); 4.13(q,J=8 Hz, 2 H ) ;

6.98 (d,J=5 Hz, 1H); 7.10-7.60(m, 6H). MS, m / z ( % ) : 232 (M+,601; 187(100). C13H1202S requires: C, 67.22; H, 5.21. Found: C, 67.11; H , 5.30. 2-Acety l -3 -pheny l th iophene (4Ib). Colourless solid. Mp. 60-61gC(from hexanes). NMR(CDC13): 1.98(s, 3H); 6.97 (d,J=5 Hz, 1H); 7.33(s, 5H); 7.45(d,J=5 H z , 1H). MS, m / z ( % ) : 202(M+,74); 187(100). C12H100S requires: C, 71 .26; H, 4.98. Found: C, 71.38; H, 5.09.

Acknowledgements

financial support (Project PB86-0145). Authors thank to the Spanish DGICYT for the

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