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Palladium-catalyzed reactions can open up short and efficient pathways from simple starting materials ... the sense of an intramolecular Heck reaction (ref. 1). a.

Pure & Appl. Chem., Vol. 68, No. 2, pp. 323-326, 1996. Printed in Great Britain. 0 1996 IUPAC

Palladacycles as intermediates in catalyzed processes to polycyclic hydrocarbons G e r a l d D y k e r , J u t t a K o r n i n g , F r a n k N e r e n z , P e t e r Siemsen, S t e f a n S o s t m a n n and Anke W i e g a n d l n s t i t u t f u r O r g a n i s c h e Chemie d e r T e c h n i s c h e n U n i v e r s i t a t Hagenring 30, D-38106 Braunschweig (FRG) P e t e r G. J o n e s and P e t e r B u b e n i t s c h e k l n s t i t u t f u r A n o r g a n i s c h e und A n a l y t i s c h e Chemie d e r Tec h n i s c h e n U n i v e r s i t at, Hag en r i n g 3 0 , 0 3 8106 B r aun s c h w e i g

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A b s t r a c t : P a l l a d a c y c l e s a r e key i n t e r m e d i a t e s o f c a t a l y z e d domino processes that lead f r o m simple s t a r t i n g materials t o polycyclic hydrocarbons. Annulated fulvenes, sesquifulvalenes a n d b e n z o p l e i a d i e n e s a s w e l l as v a r i o u s a r y l a n n u l a t e d p r o p e l l a n e s a r e e f f i c i e n t l y a c c e s s i b l e by t h e s e p r o c e s s e s .

P a l l a d i u m - c a t a l y z e d r e a c t i o n s c a n open up s h o r t and e f f i c i e n t p a t h w a y s f r o m simple s t a r t i n g materials t o complex t a r g e t molecules ( r e f . 1). Very o f t e n palladacycles are key intermediates of these processes. I n these cases t h e r i n g size of the palladacycles i s o f special importance.

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Domino Reactions One o f s e v e r a l w a y s ( r e f . 21 a p a l l a d a c y c l e c a n be f o r m e d i s t h e c y c l o p a l l a d a t i o n r e a c t i o n o f a s u b s t r a t e 1 w i t h a r e a c t i v e h a l o g e n a t o m X and a h y d r o g e n in a suitable distance. This i s a very general reaction scheme: in principle t h e c e n t r e s c o n n e c t e d w i t h b o l d l i n e s c a n be s p 2 - h y b r i d i z e d as w e l l a s s p 3 - h y b r i dized. B o t h , c a r b o n a t o m s a n d h e t e r o a t o m s a r e allowed, b u t i n t h i s b r i e f o v e r view we w i l l f o c u s on h y d r o c a r b o n s e x c l u s i v e l y . A 6 - m e m b e r e d p a l l a d a c y c l e 2 r a p i d l y t r a n s f o r m s t o a 5 - m e m b e r e d r i n g 2 by r e d u c t i v e e l i m i n a t i o n o f PdO, t h a t w i l l r e e n t e r a n d t h e r e f o r e c l o s e t h e c a t a l y t i c c y c l e . 5 - m e m b e r e d p a l l a d a c y c l e s 3 behave d i f f e r e n t l y . The f o r m a t i o n o f 4 - m e m b e r e d r i n g s 6 i s u n f a v o u r a b l e . b u t n o t i m p o s s i b t e a s w e w i l l see b e l o w . The 5-membered palladacycles c a n b e v e r y u s e f u l as r e a c t i v e i n t e r m e d i a t e s b e c a u s e t h e y o p e n up p a t h w a y s t o domino r e a c t i o n s ( r e f . 3) by r e a c t i n g w i t h a second m o l e c u l e o f t h e s u b s t r a t e 4 o r w i t h added r e a g e n t s . T h i s b e c o m e s p o s s i b l e , just because the competing reductive elimination i s relatively slow. Various polyc y c l i c h y d r o c a r b o n s a n d even p r o p e l l a n e s a r e e a s i l y a c c e s s i b l e by s u c h p r o c e s s e s .

323

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G . DYKER eta/.

The p h e n y l - s u b s t i t u t e d o l e f i n i c b r o m i d e 1 as w e l l a s t h e c o r r e s p o n d i n g i o d i d e i s e f f i c i e n t l y t r a n s f o r m e d by a P d - c a t a l y z e d domino c o u p l i n g p r o c e s s t o t h e 1 m o l - X p a l l a d i u m a c e t a t e i s s u f f i c i e n t . The a c t i v e P d O - c a t a annulated f u l v e n e lyst is formed in s i t u under the reaction conditions. According t o our mechanistic interpretation, a cyclometallation step leads t o the 5-membered palladacycle 9 ( A d d i t i o n a l l i g a n d s a r e o m m i t e d f o r c l a r i t y ) . The r e d u c t i v e e l i m i n a t i o n o f Pdo i s i n h i b i t e d i n t h i s c a s e , b e c a u s e t h e r e s u l t w o u l d be a h i g h l y s t r a i n e d and a n t i a r o matic benzocyclobutadiene. Instead, the palladacycle 9 adds another equivalent s t a r t i n g m a t e r i a l p r e s u m a b l y t o give the P d - i n t e r m e d i a t e lo o r i t s r e g i o i s o m e r with the palladium a t o m a t the vinyl position. The final r i n g closure proceeds in the sense o f an i n t r a m o l e c u l a r Heck r e a c t i o n ( r e f . 1 ) .

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X = I :92%

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a : 1 Mol - % Pd(OAc)2, K2CO3, n-Bu4NBr,

DMF,N2,3d,100°C. W e have t e s t e d s c o p e a n d l i m i t a t i o n s o f t h i s n e w s y n t h e s i s f o r a n n u l a t e d f u l v e n e s by i n t r o d u c i n g a b r i d g e b e t w e e n t h e p h e n y l s u b s t i t u e n t s . The s u b s t r a t e s 11 a n d 1 2 w i t h s e v e n - m e m b e r e d a n d s i x - m e m b e r e d c e n t r a l r i n g s give t h e s a m e r e a c t i o n and l e a d t o t h e a n n u l a t e d f u l v e n e s 1 4 and 1 3 w i t h e x c e l l e n t y i e l d s i n t h e r a n g e o f 9 0 X. W i t h t h e f l u o r e n o n e d e r i v e d s u b s t r a t e 1 3 w e h a v e f i n a l l y r e a c h e d t h e l i m i t o f t h e new a n n u l a t i o n r e a c t i o n . I n t h i s c a s e t h e f o r m a t i o n o f an e s p e c i a l l y strained fulvene does not occur, probably because the cyclopalladation step i s inhibited. Instead. a palladium catalyzed Ullmann coupling reaction ( r e f . 4 ) takes place leading t o product 13. Through cross coupling reactions of olefinic bromides w i t h substituted alkynes ( f o r c o m p a r i s o n : r e f . 5 ) some i n t e r e s t i n g p r o d u c t s b e c o m e e a s i l y a c c e s s i b l e . By t h e c o n d e n s a t i o n o f t h e s u b e r e n o n e d e r i v e d s u b s t r a t e 11 w i t h d i p h e n y l a c e t y l e n e t w o main products a r e formed. the sesquifulvalene and t h e benzopleiadiene 1 1 . T h e p r o d u c t r a t i o i s s t r o n g l y i n f l u e n c e d by t h e r e a c t i o n c o n d i t i o n s . A h i g h e r c o n c e n t r a t i o n o f t h e b r o m i d e 1 w i t h an e x c e s s o f t h e a l k y n e l e a d s m a i n l y t o t h e formation of product ( 6 4 X I . A h i g h e r d i l u t i o n and a one t o one r a t i o o f t h e c o u p l i n g c o m p o n e n t s , c o n d i t i o n s t h a t f a v o u r t h e c y c l o p a l l a d a t i o n t o 20, a r e g i v i n g r i s e t o t h e f o r m a t i o n o f t h e a n n u l a t i o n p r o d u c t le. I n t h e l a t t e r c a s e 1 3 i s i s o l a t e d w i t h 5 7 X yield, w h e r e a s 11 i s a b y p r o d u c t w i t h l e s s t h a n 3 X y i e l d . The r e a c t i o n o f t h e f l u o r e n e s y s t e m 1 3 i s o n c e a g a i n a s p e c i a l c a s e . S u r p r i singly the spirocycle 19 i s the main product confirmed by a x-ray s t r u c t u r e . On the f i r s t glimpse this substituted cyclopentadiene looks r a t h e r complicate, but w i t h p a l l a d a c y c l e s l i k e 21 as r e a c t i v e i n t e r m e d i a t e s i t s f o r m a t i o n i s e a s i l y e x p l a i n e d . A c c o r d i n g t o s e m i e m p i r i c a l c a l c u l a t i o n s 1_9 i s i n d e e d t h e t h e r m o d y n a m i c a l l y m o s t s t a b l e o f t h e f i v e double bond i s o m e r s . 0 1996 IUPAC, Pure and Applied Chemistry68.323-326

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21 A s a n i n t e r e s t i n g t a r g e t m o l e c u l e f o r p a l l a d i u m c a t a l y z e d p r o c e s s e s w e have c h o s e n t h e a n n u l a t e d p e n t a l e n e s y s t e m 25. B e c a u s e o f t h e t e d i o u s a n d r a t h e r inefficient l i t e r a t u r e procedure ( r e f . 6 ) f o r i t s synthesis not much was known a b o u t t h e r e a c t i v i t y o f t h i s m o l e c u l e . W e have f o u n d t h a t i t c a n be s y n t h e s i z e d i n a s i n g l e p r e p a r a t i v e s t e p by c o u p l i n g a c e n a p h t h y l e n e 22 w i t h 1,8-diiodonapht h a l e n e 23. A l s o i n t h i s c a s e a p a l l a d a c y l e (24)i s a s s u m e d a s an i n t e r m e d i a t e .

T h e c e n t r a l double b o n d o f 25 o f f e r s o p p o r t u n i t i e s f o r t h e c o n s t r u c t i o n o f p r o p e l l a n e s by v a r i o u s c y c l o a d d i t i o n r e a c t i o n s . S u r p r i s i n g l y t h i s double b o n d i s r e active enough t o t a k e p a r t i n palladium-catalyzed annulation r e a c t i o n s ( r e f . 7). The p u r p l e h e x a c y c l i c h y d r o c a r b o n 25 r e a c t s w i t h i o d o b e n z e n e u n d e r p a l l a d i u m c a t a l y s i s t o give t h e C4.3.33propellane 26 w i t h 7 2 X y i e l d . T h i s i s q u i t e a n u n u s u a l reaction, i n f a c t i t s the f i r s t example of an intermolecular Heck-type r e a c t i o n at a t e t r a s u b s t i t u t e d d o u b l e bond. P r e s u m a b l y a p h e n y l - p a l l a d i u m - s p e c i e s a d d s t o t h e d o u b l e bond o f 2 5 , f o l l o w e d by a c y c l o m e t a l l a t i o n t o t h e p a l l a d a p r o p e l l a n e 2. A d d i t i o n o f a s e c o n d e q u i v a l e n t o f i o d o b e n z e n e f i n a l l y l e a d s t o 26.

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The r e a c t i o n w i t h i o d o p r e h n i t e n e ( 1 - i o d o - 2 , 3 , 8 , 5 - t e t r a r n e t h y l b e n z e n e ) takes a surprizing course; as the only isolated product we obtained t h e L3.3.2lpropellane 27 i n 2 2 X yield. Presumably because o f s t e r i c hindrance the addition o f a second m o l e c u l e a r y l i o d i d e t o t h e p a l l a d a p r o p e l l a n e i n t e r m e d i a t e 30 i s i n h i b i t e d . I n t h i s special case reductive elimination t o the four-membered r i n g occurs.

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A f a s c i n a t i n g t a r g e t i s o f c o u r s e t h e s y m m e t r i c a l C 3 . 3 . 3 l p r o p e l l a n e 28. A s i t t u r n e d o u t , i t i s e a s i l y s y n t h e s i z e d by t h e p a l l a d i u m - c a t a l y z e d r e a c t i o n w i t h l - i o d o n a p h t h a l e n e (37 X y i e l d ) . I n t h i s c a s e t h e s i x - m e m b e r e d p a l l a d a c y c l e 31 i s p r o bably a n i n t e r m e d i a t e . 0 1996 IUPAC, Pure and Applied Chemistry 68,323-326

326

G . DYKER eta/.

The r i n g s t r a i n o f t h e C3.3.33propellane 28 i s i l l u s t r a t e d by t h e x - r a y s t r u c t u r e w i t h b o n d a n g l e s o f 109" a t s p 2 - h y b r i d i z e d c a r b o n c e n t r e s a n d an e l o n g a t e d c e n t r a l b o n d w i t h a l e n g t h o f 162 pm, c o m p a r e d t o 1 5 4 p m o f a n o r m a l C - C s i n g l e bond. F i g u r e 1 g i v e s i m p r e s s i o n s o f t h e c r y s t a l p a c k i n g o f 28: a p e r s p e c t i v e o f t h e t h r e e - d i m e n s i o n a l l a t t i c e and an o v e r v i e w o f a s p a c e f i l l i n g mono l a y e r . T w o o f t h r e e n a p h t h a l e n e u n i t s have p a r a l l e l s l i g h t l y s h i f t e d n e i g h b o u r s i n t h e d i s t a n c e o f 3 5 0 pm. t h e t y p i c a l v a n - d e r - W a a l s d i s t a n c e . The t h i r d one i s d i r e c t e d t o t h e a x i s of t h e n e x t m o l e c u l e . D e s p i t e o f t h e i m p r e s s i v e b o n d l e n g t h o f t h e c e n t r a l s i n g l e b o n d t h e C 3 . 3 . 3 l p r o p e l l a n e 28 i s t h e r m o d y n a m i c a l l y v e r y s t a b l e . U n t i l 400 OC no change o f t h e c o l o u r l e s s c r y s t a l s o c c u r s . C u r r e n t l y t h e r e a c t i v i t y o f the synthesized propellanes i s studied, especially w i t h r e g a r d t o the strained c e n t r a l s i n g l e bond.

Fig. 1: I m p r e s s i o n s o f t h e c r y s t a l p a c k i n g o f t h e C 3 . 3 . 3 l p r o p e l l a n e

28.

I n s u m m a r i z a t i o n , w e have d e s c r i b e d some d o m i n o c o u p l i n g p r o c e s s e s w i t h p a l ladacycles as reactive intermediates. These processes a r e useful f o r the cons t r u c t i o n o f a n n u l a t e d 4-, 5 - and 6 - m e m b e r e d r i n g s w i t h s p e c i a l e m p h a s i s on f u l v e n e s , s e s q u i f u l v a l e n e s a n d b e n z o p l e i a d i e n e s . F i n a l l y we have i n t r o d u c e d a new e n t r y t o s t r a i n e d p r o p e l l a n e s .

ACKNOWLEDGEMENT F i n a n c i a l s u p p o r t o f t h e "Fonds d e r C h e m i s c h e n I n d u s t r i e " . o f t h e " V o l k s w a g e n S t if t u n g ", o f t h e '' D e u t s c h e F o r s c h u n g s g e m e in s c h a f t *' i s g r e a t f u l l y ac k n o w l e d g e d . S p e c i a l t h a n k s t o P r o f . D r . H. H o p f f o r p r o v i d i n g l a b s p a c e and e q u i p m e n t .

REFERENCES

1. 2. 3. 4. 5. 6. 7.

de M e i j e r e and F. E. M e y e r , A n g e w . C h e m . I n t . E d . E n g l . 3 3 , 2 3 7 9 ( 1 9 9 4 ) . D. Ryabov. C h e m . Rev. 90, 4 0 3 ( 1 9 9 0 ) . F. T i e t z e and U. B e i f u s s , A n g e w . C h e m . I n t . E d. E ngl. 3 2 , 131 ( 1 9 9 3 ) . B r i n g m a n n e t al., A n g e w . Chem. I n t . E d . E ngl. 29, 9 7 7 ( 1 9 9 0 ) . J. S i l v e r b e r g e t at., J . O r g a n o m e t . C h e m . 4 0 9 , 411 (1991). R. H . M i t c h e l l e t al., Can. J. Chem. 5 5 , 1480 ( 1 9 7 7 ) . G. D y k e r e t al., A n g e w . C h e m . I n t . Ed. E ngl. 3 2 , 1 7 3 3 ( 1 9 9 3 ) . A. A. L. G. L.

0 1996 IUPAC, Pure and Applied Chemistry 68,323-326