Catalytic Aspects of Metal Phosphine Complexes - American

12

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Palladium-Triarylphosphine Complexes as Catalysts for Vinylic Halide Reactions R. F. H E C K Department of Chemistry, University of Delaware, Newark, DE 19711

Palladium

acetate-triarylphosphine

the addition olefinic

of vinylic

compounds

groups

complexes

from

vinylic

in the presence

of amines.

gated dienes are major

products

acids, esters, or nitriles

while unactivated

pounds

from

react best in the presence

where allylic

amines

olefinic

are major products.

is illustrated

to

Conju

α,β-unsaturated

of secondary

are usually regio- and stereospecific. ity of the reaction

catalyze halides

The

com amines

reactions

The synthetic

with a wide variety

util of

examples.

P

a l l a d i u m - t r i a r y l p h o s p h i n e complexes are catalysts for the reac tion

of

aryl, heterocyclic, b e n z y l ,

olefins and amines (I). ladium^)

and

v i n y l i c halides

with

T h e usual catalyst is a combination of pal

acetate w i t h two equivalents of a triarylphosphine. T h e

complex that is formed is r e d u c e d i n situ i n the reaction mixtures to an active Pd(0) phosphine complex (see Equations 1, 2, 3, and 4 w h i c h depict catalyst formation). T h i s species then oxidatively adds the or ganic halide (see E q u a t i o n 2) and the adduct i n turn adds to the olefinic reactant (see E q u a t i o n 3). T h e organic group adds mainly or often exclusively to the less-substituted olefinic carbon. T h i s addition product is generally unstable because sp

3

carbon-hydrogen

bonds

usually w i l l be i n positions beta to the p a l l a d i u m group, a n d /3-hydride elimination of the p a l l a d i u m h y d r i d e group w i l l occur. T h e e l i m i n a tion produces olefin-π-complexes

initially. After dissociation or dis

placement of the h y d r i d o p a l l a d i u m halide group from the π complex, the h y d r i d e decomposes into the Pd(0)

phosphine complex and hy

drogen halide. T h e hydrogen halide is neutralized b y the amine pres ent. T h e Pd(0) complex then reacts with the organic halide again a n d the cycle is repeated. 0065-2393/82/0196-0213$05.00/0 © 1982 American Chemical Society

In Catalytic Aspects of Metal Phosphine Complexes; Alyea, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

214

M E T A L PHOSPHINE COMPLEXES

Pd(OAc) L 2

°'

2

ePdL

+ o l e f i n i c acetates

n

L, - H O A c

η = 2, 3, or 4

(1)

R X + PdL„ - » R P d L X + (n - 2)L

(2)

2

Η

Η \

RPdL X +


2

/

C = C

I

-L

I

R—C—C—PdL X

(3)

2

L

I

I

H—Pd—X R

Î

R

\ = C ^

H X L R

4- [ H P d L X ] 2

PdL X + R N PdL + R NH X" = Br, I = P A r o r i f X = I, s o l v e n t , o l e f i n , e t c . = a r y l , h e t e r o c y c l i c , b e n z y l , or v i n y l i c g r o u p 2

3

n

3

(4)

+

3

We are presently concentrating o n u s i n g v i n y l i c halides i n this reaction. T h e v i n y l i c h a l i d e reactions are often m o r e c o m p l i c a t e d t h a n t h e b a s i c r e a c t i o n s h o w n i n E q u a t i o n s 1 t h r o u g h 4 (2). T h e first c o m p l i c a t i o n occurs i n the oxidative a d d i t i o n step. If the v i n y l i c h a l i d e exists i n i s o m e r i c forms, the o x i d a t i v e a d d i t i o n occurs w i t h

complete

retention o f stereochemistry. A d d i n g the v i n y l i c p a l l a d i u m c o m p l e x to the olefin occurs to place the organic group o n the least-substituted o l e f i n i c c a r b o n o r o n t h e m o r e d i s t a n t c a r b o n i f o n e is s u b s t i t u t e d w i t h a s t r o n g l y e l e c t r o n - w i t h d r a w i n g g r o u p (see E q u a t i o n s 5, 6, a n d 7). T h e β-hydride e l i m i n a t i o n takes p l a c e l a r g e l y or e x c l u s i v e l y to form the conjugated

d i e n e π-complex. D i s s o c i a t i o n o f t h e π-complex or d i s

p l a c e m e n t o f the d i e n e from the π-complex n o w m a y occur, e s p e c i a l l y i f c a r b o n y l , n i t r i l e , or aryl groups are conjugated w i t h the d i e n e system (see E q u a t i o n 6). I f loss o f t h e h y d r i d o p a l l a d i u m g r o u p o c c u r s , t h e double

bond

originating

from

the v i n y l i c

halide

will

retain the

stereochemistry o f that h a l i d e a n d the second d o u b l e b o n d w i l l b e f o r m e d w i t h s t e r e o c h e m i s t r y r e s u l t i n g from a s y n a d d i t i o n o f t h e v i nylpalladium group followed b y a s y n elimination of the hydridopal l a d i u m g r o u p . I f there is a c h o i c e o f h y d r o g e n s for t h e s y n e l i m i n a t i o n , the t h e r m o d y n a m i c a l l y

more stable d o u b l e

b o n d isomers are pre

ferred. H o w e v e r the dissociation o f the h y d r i d e g r o u p or the d i s p l a c e m e n t o f t h e d i e n e f r o m t h e 7 r - c o m p l e x e s is o f t e n less f a v o r a b l e t h a n t h e


12.

HECK

Palladium-Triarylphosphine

Complexes

215

PdLX PdL X 2

+

R'

R


(5)

R' +

(6)

HPdUX

X-

(7)

r e a d d i t i o n o f t h e h y d r i d e t o t h e d i e n e g r o u p to f o r m 7 r - a l l y l i c p a l l a d i u m h a l i d e c o m p l e x e s . O n l y w h e n the d i e n e s are conjugated ester, n i t r i l e , carboxylate, dridopalladium group

from

or a r y l groups

does the loss of the

the 7r-complex occur easily. I n the

cases, t h e π-allylic p a l l a d i u m h a l i d e i n t e r m e d i a t e s

with hyother

are u s u a l l y resis

tant to further r e a c t i o n w i t h o u r n o r m a l base t r i e t h y l a m i n e . H o w e v e r w e c a n cause a c a t a l y t i c r e a c t i o n to o c c u r i f a n u c l e o p h i l i c

secondary

a m i n e is u s e d i n s t e a d o f t r i e t h y l a m i n e . T h i s v a r i a t i o n p r o d u c e s t e r t i a r y


216


a l l y l i c a m i n e s b y n u c l e o p h i l i c attack o f the secondary a m i n e o n the π-allylic c o m p l e x (see E q u a t i o n 7). T w o a m i n e p r o d u c t s a r e p o s s i b l e s i n c e t h e n u c l e o p h i l e m a y a t t a c k at e i t h e r o f t h e t e r m i n a l c a r b o n s o f t h e a l l y l i c s y s t e m . T h e p o s i t i o n o f r e a c t i o n is v e r y s e n s i t i v e t o t h e s t e r i c e n v i r o n m e n t o f t h e a l l y l i c c a r b o n s a n d o f t e n t h e n u c l e o p h i l i c a t t a c k is q u i t e s e l e c t i v e a n d o n l y a s i n g l e a l l y l i c a m i n e is f o r m e d .


T h i s r e a c t i o n is v e r y g e n e r a l a n d u s e f u l for f o r m i n g m a n y p o l y f u n c t i o n a l a l i p h a t i c c o m p o u n d s since the a m i n e p r o d u c t s are c o n verted easily into other types o f c o m p o u n d s . Before d i s c u s s i n g examples of the reactions, it s h o u l d b e p o i n t e d out that most types o f v i n y l i c h a l i d e s u s e d i n this reaction are easily a v a i l a b l e . T h e U V - c a t a l y z e d a d d i t i o n o f H B r to t e r m i n a l acetylenes f o r m s t h e 1 - b r o m o - l - a l k e n e s . T h e c i s i s o m e r is f o r m e d a l m o s t e x c l u s i v e l y i f t h e a d d i t i o n is c a r r i e d o u t at d r y i c e t e m p e r a t u r e . T h e 2 - b r o m o or 2 - i o d o - l - a l k e n e s are o b t a i n e d from r e a c t i n g aqueous h y d r o g e n h a l i d e s w i t h a l k y n e s . T h e 2 - s u b s t i t u t e d - 1 - b r o m o - l - a l k e n e s are a v a i l able b y the b r o m i n a t i o n - b a s e d e h y d r o b r o m i n a t i o n reactions.

Chain

Extension

Substitution

and Functionalization

with the

Vinylic

Reaction

T h e m a j o r v a l u e o f t h e v i n y l i c h a l i d e - o l e f i n - a m i n e r e a c t i o n is for s y n t h e s i z i n g p o l y f u n c t i o n a l a l i p h a t i c c o m p o u n d s . T h e c o m p o u n d s are constructed from the v i n y l i c h a l i d e , the olefinic reactant w i t h the nec e s s a r y s u b s t i t u e n t s , a n d a s e c o n d a r y a m i n e (or t e r t i a r y a m i n e i f a c t i v a t i n g g r o u p s a r e p r e s e n t i n t h e a p p r o p r i a t e p o s i t i o n s ) . It is p o s s i b l e t o h a v e various f u n c t i o n a l g r o u p s present i n either the h a l i d e or the o l e f i n i c c o m p o u n d a n d t h e r e is a c h o i c e o f w h i c h p a r t o f t h e m o l e c u l e is t h e o l e f i n i c r e a c t a n t a n d w h i c h p a r t is t h e v i n y l i c h a l i d e . It is u s e f u l t o c l a s s i f y f u n c t i o n a l i z e d o l e f i n s i n t o g r o u p s a c c o r d i n g to t h e n u m b e r o f c a r b o n a t o m s t h e y a d d t o t h e v i n y l i c d o u b l e b o n d o f t h e h a l i d e i n t h e r e a c t i o n . U s e f u l r e a c t a n t s a r e l i s t e d i n T a b l e I. S o m e success has b e e n a c h i e v e d u s i n g a l l o f the a b o v e olefinic c o m p o u n d s i n reactions w i t h v i n y l i c h a l i d e s a n d a m i n e s to a d d the n u m b e r o f carbons i n d i c a t e d , s e l e c t i v e l y to form one i s o m e r i c p r o d u c t or o n e w h i c h is s e p a r a t e d e a s i l y f r o m a m i x t u r e t h a t m a y h a v e b e e n formed. N u m e r o u s other s i m i l a r reagents m a y be i m a g i n e d , b u t either t h e y h a v e not b e e n t r i e d or successful reactions w e r e not f o u n d . T a b l e II shows a s i m i l a r classification o f f u n c t i o n a l i z e d v i n y l i c halides.


12.

HECK


T a b l e I. 2

217

F u n c t i o n a l i z e d Olefins U s e f u l i n the V i n y l i c Substitution Reaction 3

Carbons

Carbons

CH2=CHC0 R(H)

C H 2 = C H 2

2

CH2=CHSR

C H 2 = C H C N

(3)

C C C C

Ο


Complexes

CH =CHN 2

H2=CHCONH H2=CHCH(OR) H ^ C H C H . O H H2=CHCH NR 2

2

2

2

6

Carbons

T h e c h o i c e as to w h i c h f r a g m e n t o f t h e m o l e c u l e t o b e s y n t h e s i z e d s h o u l d b e the v i n y l i c h a l i d e a n d w h i c h s h o u l d be the olefin w i l l de p e n d o n s e v e r a l factors. I n the cases w h e r e e l i m i n a t i o n to f o r m c o n j u g a t e d d i e n e s is t h e f a v o r e d r e a c t i o n , e i t h e r p o s s i b l e c o m b i n a t i o n o f v i n y l i c h a l i d e a n d olefin m a y p r o d u c e the same d i e n e ; however, ferent

intermediates

are i n v o l v e d

a n d i n some

instances

dif

different

p r o d u c t s m a y b e f o r m e d . T h e s i t u a t i o n is m o r e c o m p l e x w h e n a l l y l i c a m i n e s are p r o d u c e d since these p r o d u c t s a l w a y s w i l l b e from

the t w o

T a b l e II. 2 Carbons

different

different

c o m b i n a t i o n s o f reactants. For e x a m p l e ,

Z-

F u n c t i o n a l i z e d V i n y l i c B r o m i d e s U s e f u l i n the V i n y l i c Substitution Reaction 3 Carbons

4 Carbons

5

ROCH CH=CHBr 2


Carbons

218



1-bromo-l-hexene a n d ethylene w i t h morpholine produce m a i n l y Z - 2 - m o r p h o l i n o - 3 - o c t e n e ( 8 4 % ) w h i l e v i n y l b r o m i d e a n d 1-hexene w i t h m o r p h o l i n e g i v e m a i n l y Ε-l-morpholino-2-octene ( 8 4 % ) (2).

T h e r e is a l s o t h e p o s s i b i l i t y t h a t o n e c o m b i n a t i o n o f r e a c t a n t s w i l l g i v e m o r e i s o m e r i c p r o d u c t s t h a n the other. F o r e x a m p l e , this m a y o c c u r w h e n e l e c t r o n - d o n a t i n g substituents are present i n the olefinic r e a c t a n t . T h i s effect is s e e n i n t h e r e c i p r o c a l r e a c t i o n s o f m e t h y l j 3 - b r o m o m e t h a c r y l a t e w i t h 1-hexene a n d o f Z - 1 - b r o m o - l - h e x e n e w i t h


HECK


Complexes


12.


219


220


m e t h y l m e t h a c r y l a t e . I n t h e first c o m b i n a t i o n , t h r e e m o r e i s o m e r s a r e f o r m e d t h a n i n t h e s e c o n d c o m b i n a t i o n b e c a u s e t h e a d d i t i o n to 1-hexene o c c u r s a b o u t 8 0 % o n t h e t e r m i n a l c a r b o n a n d 2 0 % o n t h e s e c o n d c a r b o n , w h i l e Z - l - b r o m o - 1 - h e x e n e a d d s e x c l u s i v e l y to t h e ter m i n a l c a r b o n o f m e t h y l m e t h a c r y l a t e (4). O t h e r factors to c o n s i d e r i n c h o o s i n g r e a c t a n t s a r e r e l a t i v e rates o f r e a c t i o n ( n o t e t h e l a r g e differ ence i n the above examples) a n d the a v a i l a b i l i t y o f reactants. C o n t r o l o f t h e s e l e c t i v i t y o f t h e a d d i t i o n o f t e n is b e s t a c h i e v e d b y c h o o s i n g t h e p r o p e r r e a c t a n t s . T h e m a j o r i n f l u e n c e is s t e r i c . T h e or g a n i c p o r t i o n o f the o r g a n o p a l l a d i u m i n t e r m e d i a t e n o r m a l l y a d d s to the less-hindered, d o u b l e - b o n d carbon o f the olefin. T h e secondary e l e c t r o n i c effect is t o c a u s e t h e o r g a n i c g r o u p t o a d d t o t h e m o r e electron-deficient d o u b l e - b o n d c a r b o n . T h e structure o f the v i n y l i c h a l i d e also m a y influence the selectivity of the a d d i t i o n . B o t h v i n y l b r o m i d e a n d 2-bromopropene (and other internal v i n y l i c halides) a d d s e l e c t i v e l y to t h e t e r m i n a l d o u b l e - b o n d c a r b o n o f 1 - h e x e n e . H o w ever j8-alkyl-substituted v i n y l i c halides give mixtures of adducts w i t h t h e t e r m i n a l a d d u c t s g e n e r a l l y p r e d o m i n a t i n g (2) (see T a b l e III).

V i n y l i c S u b s t i t u t i o n P r o d u c t i o n s from 1 - H e x e n e a n d Various V i n y l i c Bromides and M o r p h o l i n e

Table III.

Terminal Internal Addition of Vinylic Groups to 1-Hexene

Bromide ^ \

B

^

r

x

B r

Br

C H

3

0

2

Amines

Dienes

>20

84

4

> 20

64

16

1.8

34

18

1.8

42

15

1.7

31

13

4.6

—

72

Br

^

^

% Yield of Terminal Adducts

x

Br

C — f ^ ^ B r

(Et N) 3


12.

HECK


221

Complexes H


+

It

is

interesting

and

of

preparative

value

that

isomers

although

1-

b r o m o - 2 - m e t h y l - l - p r o p e n e a n d s i m i l a r h a l i d e s a d d t o 1 - h e x e n e at b o t h d o u b l e - b o n d carbons, o n l y one o f the t w o ^ a l l y l i c intermediates re acts w i t h t h e a m i n e . T h e r e s u l t is t h a t a m i x t u r e o f six i s o m e r i c d i e n e s is f o r m e d , b u t o n l y o n e a l l y l i c a m i n e is p r o d u c e d . T h e r e f o r e t h e r e a c t i o n is u s e f u l s i n c e t h e d i e n e s a n d t h e a m i n e a r e s e p a r a t e d e a s i l y (2).

H

T h e r e a s o n for t h e s e l e c t i v e f o r m a t i o n o f t h e h i g h l y h i n d e r e d N - t e r t i a r y a l k y l a m i n e i s o m e r a p p e a r s t o b e t h a t t h e t e r t i a r y π-allylic c a r b o n is m o r e s u s c e p t i b l e to n u c l e o p h i l i c a t t a c k b y t h e a m i n e t h a n t h e s e c o n d ary c a r b o n , p r e s u m a b l y b e c a u s e o f the w e a k e r p a l l a d i u m - t e r t i a r y car b o n b o n d . S i m i l a r results have b e e n observed i n several related reac tions.


222

M E T A L PHOSPHINE


Reactions of Functionalized

COMPLEXES

Olefins

C o n s i d e r i n g f u n c t i o n a l i z e d o l e f i n s first, o n l y t h r e e t w o - c a r b o n reactants are l i s t e d a b o v e . E t h y l e n e i t s e l f c a n g i v e o n l y t e r m i n a l d o u b l e b o n d s w h e n e l i m i n a t i o n is f a c i l e a n d t r i e t h y l a m i n e f u n c t i o n s as t h e b a s e . I f n u c l e o p h i l i c s e c o n d a r y a m i n e s are n e c e s s a r y , e t h y l e n e p r o duces i n t e r n a l a m i n e s almost entirely. A r y l h a l i d e s react w e l l w i t h e t h y l e n e to p r o d u c e s t y r e n e d e r i v a t i v e s . T r o s t h a s u s e d v i n y l t h i o e t h e r s to a d d t w o c a r b o n s w i t h t e r m i n a l f u n c t i o n a l i z a t i o n (3). V i n y l e t h e r s a n d v i n y l a c e t a t e g i v e m i x t u r e s o f p r o d u c t s w h i l e i s o p r o p e n y l acetate reacts s e l e c t i v e l y w i t h a r y l h a l i d e s a n d at l e a s t o n e v i n y l i c h a l i d e .

OAc ι W e h a v e l o o k e d at a d d i t i o n s t o N - v i n y l p h t h a l i m i d e b r i e f l y . A r y l a n d v i n y l i c h a l i d e s a d d easily, b u t w e have not yet f o u n d a g o o d m e t h o d to h y d r o l y z e t h e s e a d d u c t s to a l d e h y d e s . A d d i t i o n s to f u n c t i o n a l i z e d three-carbon olefins h a v e b e e n stud i e d e x t e n s i v e l y . W e h a v e u s e d m e t h y l a c r y l a t e as a s t a n d a r d o l e f i n s i n c e i t a l w a y s r e a c t s o n l y at t h e t e r m i n a l c a r b o n a n d t h e α,/3-double b o n d i n t h e p r o d u c t is a l w a y s t r a n s . T h e s t e r e o s p e c i f i c i t y o f its r e a c t i o n s w i t h v i n y l i c h a l i d e s v a r i e s w i t h s t r u c t u r e . T h e s i m p l e 1halo-l-alkenes w i t h m e t h y l acrylate u n d e r normal conditions give mix t u r e s o f E , Z - a n d Ε,Ε-dienoates. T h e r e a c t i o n is m o r e s e l e c t i v e w i t h the b r o m i d e s t h a n w i t h the iodides a n d the stereoselectivity increases w i t h increasing t r i p h e n y l p h o s p h i n e concentration. T h i s occurs be cause the excess p h o s p h i n e displaces the h y d r i d o p a l l a d i u m h a l i d e g r o u p f r o m t h e d i e n e π - c o m p l e x b e f o r e r e a d d i t i o n to f o r m t h e πa l l y l i c s p e c i e s o c c u r s (see E q u a t i o n 6). T h e d i s u b s t i t u t e d v i n y l i c b r o m i d e s r e a c t s t e r e o s p e c i f i c a l l y w i t h m e t h y l a c r y l a t e (4). A c r y l i c a c i d m a y b e u s e d i n p l a c e o f its esters i n t h e s e

reactions

w i t h l i t t l e or n o d i f f e r e n c e i n y i e l d p r o v i d e d a n e x t r a e q u i v a l e n t o f t h e


12.

HECK


223

Complexes .

C0 CH 2

ITf M

{

Pd(OAc) + 8PPh 100°C, 21 h 2

3

[

C0 CH 2

79%

r

Et NH Br" +

3

2Pd(OAc) + 6P(o-toi)

Br

2

^

+


"

3

13%

X

C 0

2

C H

'

3

3 r

125°C,24h

3 J N

C C X C H ,

+ EtoNH Br" +

80% Pd(OAc) + 6P(o-tol) 2

+

^ \

C

0

2

C H o

+

E

t

3

N

3

125°C,6days

C 0

2

C H

3

+

E

t

3

N

H

+

B

r

"

77% a m i n e is a d d e d t o n e u t r a l i z e t h e c a r b o x y l i c a c i d . M e t h a c r y l a t e esters a n d a c i d react s i m i l a r l y b u t more s l o w l y than the acrylates a n d a n additional

isomer

is

formed

generally.

In

these

reactions

the

α - m e t h y l e n e i s o m e r s o f t e n a r e f o r m e d . C r o t o n a t e esters (or a c i d ) a l s o react s l o w l y g i v i n g t h e t h r e e - s u b s t i t u t e d esters. A c r y l o n i t r i l e reacts easily w i t h aryl a n d v i n y l i c h a l i d e s , b u t p r o d uct m i x t u r e s are g e n e r a l l y m o r e c o m p l e x t h a n t h e ones from t h e re l a t e d reactions w i t h a c r y l a t e esters. A s i g n i f i c a n t a m o u n t o f n i t r i l e isomers w i t h cis-a,/3-double b o n d s are f o r m e d a n d these isomers are not seen i n t h e acrylate ester reactions. A c r y l a m i d e appears s i m i l a r to t h e a c r y l a t e esters, h o w e v e r w e h a v e n o t s t u d i e d i t s r e a c t i o n s i n d e t a i l . A v e r y u s e f u l t h r e e - c a r b o n o l e f i n is a c r o l e i n d i m e t h y l a c e t a l ( 5 ) . A c r o l e i n i t s e l f c a n n o t b e u s e d b e c a u s e i t p o l y m e r i z e s and/or r e a c t s w i t h amines u n d e r the normal reaction conditions. W i t h p i p e r i d i n e or m o r p h o l i n e as t h e b a s e , a c r o l e i n a c e t a l s r e a c t i n g o o d y i e l d w i t h a w i d e v a r i e t y o f v i n y l i c b r o m i d e s t o g i v e d i e n a l a c e t a l s and/or a m i n o e n a l a c e t a l s . T h e s e p r o d u c t m i x t u r e s , after b e i n g t r e a t e d w i t h e x c e s s aqueous oxalic a c i d a n d b e i n g steam d i s t i l l e d , y i e l d E,E-conjugated dienals,

usually

in

good

yields.

Methacrolein

acetals

a n d 3-

buten-2-one e t h y l e n e k e t a l also react w e l l , b u t the c r o t o n a l d e h y d e acetals d o not.


224


H I

CH(OCH ) 3

(C0 H) 2

H 0, 2

2

Pd(OAc) + 2P(o-tol) 2

+

3

100°C, 24 h

2

CHO

KXTC


76% H .Br

P d ( O A c ) + 2P(o-tol) t

3

(CO H) f

t

t

H O , 100°C

100°C, 18 h

t

CHO

A l l y l i c alcohols are another g r o u p o f v a l u a b l e three-carbon olefins (6). T h e s e r e a c t a n t s g e n e r a l l y a r e u s e f u l for p r e p a r i n g 4 - e n a l s a n d 4-enones. E l i m i n a t i n g the h y d r i d o substituent o n t h e c a r b o n b e a r i n g the h y d r o x y l g r o u p i n the i n i t i a l o r g a n o p a l l a d i u m c o m p l e x - a l l y l i c a l c o h o l a d d u c t is u s u a l l y m o r e f a v o r a b l e t h a n e l i m i n a t i n g t h e a l l y l i c h y d r i d o group. M i x t u r e s o f products are o b t a i n e d u s u a l l y , b u t often t h e c a r b o n y l p r o d u c t s a r e s e p a r a t e d e a s i l y so t h a t t h e r e a c t i o n s a r e preparatively useful. F o r example, Z - l - b r o m o - l - p r o p e n e , m e t h a l l y l a l c o h o l , a n d m o r p h o l i n e react to form a m i x t u r e o f p r o d u c t s c o n t a i n i n g t h e m o r p h o l i n e e n a m i n e o f Z - 2 - m e t h y M - h e x e n a l . I t is n o t n e c e s s a r y t o i s o l a t e t h e e n a m i n e , b u t t h e e n t i r e r e a c t i o n m i x t u r e c a n b e a d d e d to excess 5 % a q u e o u s o x a l i c a c i d a n d steam d i s t i l l e d . I n this w a y a 3 8 % y i e l d o f Z - 2 - m e t h y l - 4 - h e x e n a l is o b t a i n e d b a s e d o n t h e v i n y l i c h a l i d e . T h e p r o d u c t is e n t i r e l y t h e Z - i s o m e r . H

38% Other examples

follow:


12.

HECK


225

Complexes


H

W e have encountered isomer p r o b l e m s w i t h the a l l y l i c alcohol r e a c t i o n s , as w o u l d b e e x p e c t e d , w i t h s o m e r e a c t a n t s . F o r crotyl alcohol a n d 1-bromo-l-propene

example,

w i t h piperidine give a mixture

of two isomeric amino alcohols a n d two enamines

(6).

H

23%


M E T A L PHOSPHINE

226

COMPLEXES


T h e reactions o f tertiary a l l y l i c a m i n e s w i t h v i n y l i c h a l i d e s are r e l a t e d c l o s e l y to t h e a l l y l i c a l c o h o l r e a c t i o n s s i n c e e n a m i n e s a r e o f t e n major p r o d u c t s . W e h a v e just b e g u n w o r k i n this area a n d h a v e few results to report yet. W e h a v e seen some significant differences i n the p r o d u c t s f o r m e d from t e r t i a r y a l l y l i c a m i n e s a n d from t h e r e l a t e d a l l y l i c a l c o h o l s . A t y p i c a l e x a m p l e is t h e r e a c t i o n o f 2 - b r o m o p r o p e n e w i t h N-allylpiperidine and piperdine where a 4 2 % y i e l d of a single e n a m i n e is o b t a i n e d (6). T h e r e l a t e d r e a c t i o n w i t h a l l y l a l c o h o l g i v e s a mixture of regioisomeric enamines.

F o u r - c a r b o n - c h a i n extensions h a v e b e e n very successful w i t h c o n j u g a t e d d i e n e s as t h e f u n c t i o n a l i z e d o l e f i n s . W e h a v e u s e d a f e w o t h e r compounds a l s o , b u t t h e y are o f l i m i t e d v a l u e , s u c h as N3 - b u t e n y l p h t h a l i m i d e . T h e l a s t c o m p o u n d is o n l y u s e f u l w i t h a r o m a t i c or certain v i n y l h a l i d e s w h e r e m i x t u r e s o f a l l y l i c a m i n e s w o u l d not b e f o r m e d . A t y p i c a l d i e n e e x a m p l e is t h e r e a c t i o n o f v i n y l b r o m i d e w i t h butadiene a n d p i p e r i d i n e w h i c h gives E-N-(2,5-hexadienyl)-piperi d i n e i n 7 0 % y i e l d (7). T h e p r o d u c t o f t h i s r e a c t i o n c a n b e r e a c t e d a g a i n a n d u s e d to e x t e n d t h e c a r b o n c h a i n s b y s i x a t o m s (see b e l o w ) . T h e r e a c t i o n s o f c o n j u g a t e d d i e n e s c a n b e u s e d to p r o d u c e c o n j u g a t e d t r i e n e s a l s o (4). H I

Pd(OAc), + 2P(o-tol)

Br

100°C, 23 h

3

*

+


Br"

12.

HECK


227

Complexes

Pd(OAc) + 2P(o-tol) 2

^ C 0

2

C H

+

3

E

t

3

3

100°C, 48 h

N

C0 CH 2

3

+

Et NH Br~ +

3


81% Five-carbon-atom-chain

extensions

have

been

achieved

with

three k i n d s o f u n s a t u r a t e d c o m p o u n d s : 1,4-dienes, 2 , 4 - d i e n o i c a c i d s or esters, a n d N - 2 , 4 - d i e n y l a m i n e s . T h e 1,4-dienes a r e g e n e r a l l y

useful

w i t h aromatic halides, but give mixtures o f isomeric amines w i t h most vinylic halides because

of elimination a n d readdition of palladium

h y d r i d e i n b o t h possible directions to p r o d u c e t w o different intermediates.

E x c e p t i o n s o c c u r i n cases

7r-allylic

where symmetrical

com

pounds are being formed a n d where both directions o f elimination l e a d t o t h e s a m e p r o d u c t (8). F o r e x a m p l e :

Pd(QAc) + 2P(o-tol) 2

3

100°C, 3 days

70% 2,4-Pentadienoic

a c i d reacts w e l l w i t h aromatic h a l i d e s to g i v e

5-aryl-pentadienoic

a c i d s . T h e o n l y v i n y l i c h a l i d e s t u d i e d so f a r is

E-2-bromostyrene.

This

halide

gave

a

5 7 % yield

of

phenylheptatrienoic acid. N-(2,4-Pentadienyl)piperidine

C0 H

+ 2 Et N 3

E,E,E-7-

is v e r y u s e f u l

Pd(QAc) + 2P(o-tol) 100°C, 4 h 2

3

2

C0 H 2

57%


228


for s y n t h e s i z i n g 2 , 6 - d i e n a l s w i t h s p e c i f i c s t e r e o c h e m i s t r y at P o s i t i o n 6. A l t h o u g h the y i e l d s are not h i g h , this reaction p r o v i d e s a very s i m p l e m e t h o d for p r e p a r i n g t h e s e c o m p o u n d s . F o r e x a m p l e , v i o l e t l e a f a l d e h y d e , 2 - E , 6 - Z - n o n a d i e n a l , is e a s i l y m a d e v i a t h i s r e a c t i o n (10). T h e i n t e r m e d i a t e i n t h e r e a c t i o n is b e l i e v e d t o b e a d i e n a m i n e .


H

+ amines

O n l y o n e , s i x - c a r b o n u n i t for c h a i n l e n g t h e n i n g h a s b e e n s t u d i e d . T h i s is E - ( N - 2 , 5 - h e x a d i e n y l ) p i p e r i d i n e , p r e p a r e d as d e s c r i b e d e a r l i e r i n this chapter. T h i s c o m p o u n d reacts w i t h b r o m o b e n z e n e to g i v e a 5 5 % y i e l d o f t h e 6 - p h e n y l d e r i v a t i v e (8). T h e r e a c t i o n w i t h Z -

H

1-bromo-1-hexene also a p p e a r e d n o r m a l a n d h y d r o l y s i s gave a l o w y i e l d of the expected 2,7-dodecadienal i n a p r e l i m i n a r y experiment. (10). T h i s p r o d u c t s h o u l d b e e a s i l y r e d u c i b l e t o Z - 7 - d o d e c e n - l - o l , a pheromone of several insects.

10%(CO,H), 100°C, Η , Ο


12.

HECK


Reactions of Functionalized

229

Complexes

Vinylic

Bromides

M u c h less h a s b e e n d o n e w i t h t h e f u n c t i o n a l i z e d h a l i d e s t h a n w i t h the f u n c t i o n a l i z e d olefins. T h e o n l y t w o - c a r b o n c o m p o u n d i n this g r o u p is v i n y l b r o m i d e (or i o d i d e ) . T h i s is a v e r y u s e f u l r e a c t a n t w i t h s e c o n d a r y a m i n e s b e c a u s e t e r m i n a l a l l y l i c a m i n e s a r e u s u a l l y m a j o r or


e x c l u s i v e p r o d u c t s . W e h a v e u s e d t h i s h a l i d e for s y n t h e s i z i n g t h e p h e r o m o n e o f t h e R e d B o l l w o r m M o t h , 9 , 1 1 - d o c e c a d i e n - l - o l as f o l l o w s (9). O f t h e f o u r t h r e e - c a r b o n f u n c t i o n a l i z e d v i n y l i c h a l i d e s l i s t e d , H I

o

-OH

Pd(OAc), + 2P(o-tol). VXfC,

ο

OH

7 h

*

d) CH,I (2)

T

OH" '

(3) Δ

82% OH 8 3 % , EIZ = 2.6 o n l y t h e first t h r e e h a v e b e e n s t u d i e d so far a n d t h e s e h a v e b e e n s t u d i e d o n l y b r i e f l y . A n e x a m p l e o f the use o f £ - m e t h y l 3b r o m o - 2 - m e t h y l p r o p e n o a t e has b e e n g i v e n e a r l i e r i n this chapter. T h e 3 - b r o m o a c r y l a t e esters u n d e r g o e l i m i n a t i o n u n d e r o u r r e a c t i o n c o n d i tions a n d cannot b e u s e d ; h o w e v e r the r e l a t e d b r o m o a l d e h y d e a c e t a l s c a n b e u s e d . T h e b r o m o a c r o l e i n a c e t a l is u n s t a b l e a n d n o t v e r y u s e f u l , b u t b r o m o m e t h a c r o l e i n a c e t a l r e a c t s n o r m a l l y (4). The p y r a n y l e t h e r o f 3 - b r o m o a l l y l a l c o h o l has b e e n u s e d t o p r o d u c e a 5 0 % y i e l d o f t h e p y r a n y l e t h e r o f m e t h y l 6 - h y d r o x y s o r b a t e (9). Br

Pd(OAc)j + 2P(o-tol)

+ Et,N (CH 0) CH' 3

C0 CH

2

2

3

100°C, 13 h

3

C0 CH 2

+

3

Et NH Brs

+

(CH 0) CH 3

2

90% THPO.

.Br

Pd(OAc) + 2PPhj 2

+

/

^

X

C 0

2

C H

+ Et N 3

1 W

> ,20h C

3

THPO

•C0 CH 2

3

+

Et,NH Br-

50%


+

METAL PHOSPHINE COMPLEXES

230 We

have

i n v e s t i g a t e d 4 - b r o m o - 3 - m e t h y l - 3 - b u t e n - l - o l as a f o u r -

c a r b o n - c h a i n extender that incorporates a n isoprene unit. F i r s t exper i m e n t s s u g g e s t t h i s r e a g e n t w i l l b e u s e f u l for p r e p a r i n g s e s q u i t e r p e n e s from myrcene. H I


OH

Ο

Pd(QAc) + 2P(o-tol) ^ 2

3

100°C, 48 h

Ο

H

H

\+/ y + tetraenols OH

1

Br"

+ X Ο

41% The

five-carbon

u n i t , l - b r o m o - l , 4 - p e n t a d i e n e , is e a s i l y a v a i l a b l e

from the p a l l a d i u m - c a t a l y z e d reaction o f a l l y l b r o m i d e w i t h acetylene ( J I ) , b u t w e h a v e n o t y e t s t u d i e d its r e a c t i o n s . This

very

brief

survey

of

the

palladium-triarylphosphine-

c a t a l y z e d r e a c t i o n o f v i n y l i c h a l i d e s w i t h o l e f i n s a n d a m i n e s is i n t e n d e d t o s h o w t h e w i d e a p p l i c a b i l i t y o f t h e r e a c t i o n to s y n t h e s i z i n g n u m e r o u s types o f polyfunctional aliphatic (and aromatic) c o m p o u n d s . W e h a v e m u c h m o r e to d o i n s e v e r a l a r e a s , b u t i t is a l r e a d y c l e a r t h a t t h e r e a c t i o n w i l l b e v e r y v a l u a b l e for s y n t h e s i z i n g n u m e r o u s t y p e s o f organic compounds. Literature 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Cited

Heck, R. F. Acct. Chem. Res. 1979, 12, 146. Patel, Β. Α.; Heck, R. F. J. Org. Chem. 1978, 43, 3898. Trost, B. M.; Tanigawa, Y. J. Am. Chem. Soc. 1979, 101, 4743. Kim, J-I.; Heck, R. F., unpublished data. Patel, Β. Α.; Kim, J-I.; Bender, D. D.; Kao, L-C.; Heck, R. F., unpublished data. Kao, L-C.; Heck, R. F., unpublished data. Patel, Β. Α.; Kao, L-C.; Cortese, N. C.; Minkiewicz, J. V.; Heck, R. F. J. Org. Chem. 1979, 44, 918. Bender, D. D.; Heck, R. F., unpublished data. Patel, Β. Α.; Heck, R. F., unpublished data. Stakem, F. G.; Heck, R. F., unpublished data. Kaneda, K.; Uchiyama, T.; Fujiwara, Y.; Imanaka, T.; Teranishi, S. J. Org. Chem. 1979, 44, 55.

RECEIVED July 10, 1980.


Catalytic Aspects of Metal Phosphine Complexes - American

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