Chemical Model Showing Three Phenomena: Phosphorane â Ylide

125 Chemical Model Showing Three Phenomena: Phosphorane-->Ylide, Ylide-->Phosphorane, and Phosphorane Ylide RAMON BURGADA, YVES LEROUX, and Y. O. EL KHOSHNIEH

Downloaded by CORNELL UNIV on June 1, 2017 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch125

Laboratoire des Organo-Eléments, ERA 825, Université P. et M. Curie, Tour 44-45, 4 Place Jussieu, 5230 Paris Cédex 05, France

We have shown without any doubt the formation of carbanions obtained when t r i v a l e n t phosphorus compounds react with an acetylenic compound. Trapping of these carbanionic species with p r o t i c reagents, alcohol for instance,leads to an y l i d A. An alternative pathway involves reaction on the phosphorus atom leading to a phosphorane B.

With c y c l i c phosphite 3, when the trapping reagent used in reaction is phenol, we obtain a quantitative y i e l d of y l i d . Between 0° and 20° this y l i d undergoes a complete rearrangement leading to a phosphorane (1).

Conversely, a phosphorane is obtained at -20°C when the Ρ reagent is trimethylphosphite and methanol is the trapping species. This phosphorane undergo a complete rearrangement in a few minutes at 20°C leading to an ylid. 0097-6156/81/0171-0607S05.00/0 © 1981 American Chemical Society III

Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

608

PHOSPHORUS CHEMISTRY

When the Ρ reagent is 3 with benzoic acid as trapping species, we observe an equilibrium between ylid and phosphorane which is strongly solvent dependent, Downloaded by CORNELL UNIV on June 1, 2017 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch125

III

for instance in CCl : 8 18%-9 82% and in C H C l : 8 37%-9 63%. If the dichloromethane solution is evaporated and a new solution made with carbon t e t r a chloride then the f i r s t results(8 18% and 9 82%) are found again. In tetrachloride s o l u t i o n , these two species 8 and 9 remained e s s e n t i a l l y unchanged. With d i c h l o r o methane s o l u t i o n , the evolution takes a few hours only; NMR signals appear for 10 (Z+E) whereas the i n t e n s i t y of 8^ and 9_ signals are decreasing. When the percentage of J_0 is 60% the r e l a t i v e r a t i o of y l i d versus phosphorane remains unchanged(36%-64%>. In the end, two isomers (Z + E) corresponding to the phosphonate J_0 can be seen ( Ρ NMR). 4

2

2

3 1

It is also possible to follow the chemical modification of the system with *H NMR technique and in p a r t i c u l a r the appearance and the disappearance of doublets r e l a t i v e to H-C-C=P, H-C=C-P and H-C=C-P . Upon heating, the equilibrium shifts from (50% Z, 50% E) of 10 to isomer E . Another equilibrium ylid«F=^ phosphorane has been reported a few years ago. Nevertheless i t was obtained by addition or loss of a reagent (_2) . V

IV


125.

BURGADA E T A L .

Phosphorane-Ylide

(CH.KP

Table

Μ

β

0

( C H ) . P OC H _ 3 4 3

Η

* » - MeOH

?

609

Model

Q

1 summarizes o u r r e s u l t s ,

Trapping


- CH

Chemical

species

Ρ

MeOH

+

PhOH

•f

MeOH

+

PhOH

+

Re s u 11 s

Ί

III

POMe

J—o'

Ylid

C0 Me o

•ι I

C0 Me

Ylid

(MeO) ? 3

POMe ^ L o ^

2

PhC0 H

+

PhC0 H

+

o

2

Ylid

POMe

Ylid Table

1

I n t a b l e 1, t h e t h r e e p h e n o m e n a w h i c h c o r r e s p o n d t o t h e p a p e r ' s t i t l e a r e e n c i r c l e d . We c a n a l s o s e e t h a t t h e same r e a g e n t i . e . m e t h a n o l a l w a y s g i v e s a p h o s p h o r a n e . T h i s one is s t a b l e when t h ep h o s p h i t e r e a g e n t is a c y c l i c species. This phosphorane then undergoes a r e a r r a n g e m e n t t o a n y l i d when t h ep h o s p h i t e r e a g e n t i s a linear species (Ρ(OMe)^)· One c a n s e e a l s o t h a t w i t h t h e same t r a p p i n g reagent, phenol f o rinstance, the k i n e t i c producti s now a n y l i d . When t h e t r a p p i n g r e a g e n t i s b e n z o i c acid we h a v e a t t a i n e d t h e r m o d y n a m i c s t a b i l i t y b e t w e e n ylid and p h o s p h o r a n e . A t l o w t e m p e r a t u r e , t h e y l i d 4^ a d d s m e t h a n o l b e f o r e g i v i n g b y r e a r r a n g e m e n t a p h o s p h o r a n e 5_ wh i c h f i n a l l y lead t o a saturated phosphorane 11 .

t 4

n

OMe

C0 Me 2

P

o/ $c C0 Me 2

CH N

0Ph

MeOH -20

MeO f , 0-P,

0

M

e

OPh

CHCH

c

*Ί

C 0 Me \ ; 0 Me 3 1 P-49ppm 9


PHOSPHORUS CHEMISTRY

610

Phosphorane JJ_ is stable enough in solution to be analyzed and i d e n t i f i e d . Nevertheless, in a few days JJ_ loses phenol and not methanol to give a v i n y l phosphorane J_2 (E. s t r u c t u r e ) . MeO |^0Me A M

11

H

»

0 P—C = C ^ ϋ -— / \ •° C0 Me ° 2

+ PhOH

5 + MeOH

1

C

M e


2

We can obtain the same phosphorane J_2 by methano l y s i s of phosphorane _5, Concerning the stereochemistry of the phosphorane double-bond, we observe that the Ε isomer is the more stable. The f i r s t reaction of Table 1 gives Ζ isomer, but only traces of benzoic acid are necessary to provoke instantaneous isomerisation of Ζ to E . The mechanism probably involves an addition-elimination. , MeO OMe MeO Me υ Oune » * \ / Γ Π Mp Η 12Z 0- P ^ 2 c a t a l y t i c Am. 0 - Ρ χ. „ ' 1 2E V / > c -ThcoTs—ry j y \ \ * C0 Me^ H \ ^ ° CO^le C0 Me w

Λ

Λ%

e

v

m

N

7

2

2

Results of Table 1 and the later results seem to sh ow that through out this work we are dealing with k i n e t i c a l l y controlled reactions. Moreover, we demons tr a te that an equilibrium between JT2 and the y l i d form does not exist because this should lead to the isomeris ation of Ζ to E . When the trapping reagent is acetylene dicarboxylate i t s e l f , the reaction yields a new phosphorane which is a pentacoordinated phosphole (3). Li terature cited 1. Burgada, R ; Leroux, Y ; E l Khoshnieh, Y . O . Tetrahedron L e t t . 1980, (21), 925. 2. Schmidbaur, Η ; Stuhler, H. Angew. Chem. Int. Ed. 1972, 2, 145. 3. Burgada, R ; Leroux, Y ; El Khoshnieh, Y.O. Tetrahedron Lett. (in press). RECEIVED

June 30, 1981.


Chemical Model Showing Three Phenomena: Phosphorane â Ylide

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