Alkylation by Way of Monomeric and Polymeric Alkoxyphosphonium

31 Alkylation by Way of Monomeric and Polymeric Alkoxyphosphonium Salts D O N A L D W. HAMP and E D W A R D S. LEWIS

Downloaded by UNIV QUEENSLAND on October 14, 2014 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch031

Department of Chemistry, Rice University, P.O. Box 1892, Houston, T X 77001

There are numerous examples of the conversion of alcohols to alkylating agents using phosphorus compounds (1-5). We became interested in the use of alcohols as general alkylating agents using methyltriphenoxyphosphonium triflate according to eq. (1) and (2) (5). ROH + MeP(0Ph) -> Me(PhO) POR + PhOH Me(Ph0) P0R + Nu + Me(PhO) PO + RNu (2) 3

2

(1)

-

2

2

This procedure, although rather general and susceptible to further variation has not easily given good yields, and the desired product is contaminated with PhOH and Me(PhO)P0. To avoid the latter problems we prepared a polymer version of the reagent in which one of the phenyl groups is incorporated in polystyrene. The polymeric reagent, prepared by Scheme 1, does indeed show some of the desired reactions, but undesired side reactions, difficulty of polymer recycling and yield problems in the monomeric model system have led us to study a simpler system. 2

Scheme 1 styrene

+ p-acetoxystyrene

+

DVB +

toluene a

0097-6156/81/0171-0157$05.00/0 © 1981 American Chemical Society

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

158

PHOSPHORUS CHEMISTRY

a) H2O, p o l y v i n y l a l c o h o l benzoyl peroxide, 80° ( 6 ) . b) H N , dioxane. c) (PhO) P, 1% (PhO) P0H (7). d) MeOTf, CH C1 . e) ROH, CH CN. 4

3

2

2

2

2

3

The polymer bound triphenylphosphine oxide, 1b, is r e a d i l y converted to the ditriflate, 2b, f o l l o w i n g Hendrickson and Schwartzman s procedure f o r the s y n t h e s i s of triflyltriphenylphosphonium t r i f l a t e , 2a, ( 8 ) . Much of our work has been the e x p l o r a t i o n of the monomeric system, f i r s t the conversion of the a l c o h o l to R 0 P ( P h ) 0 T f ~ and the subsequent r e a c t i o n s of these with v a r i o u s n u c l e o p h i l e s . 1

+


3

Scheme 2

la,

2a, 3a, R=H.

l b , 2b, 3b, R=polymer

a) L i P P h , THF. b) M 0 , acetone. c) T f 0 , C H C 1 , -78°. d) ROH, 2 , 6 - l u t i d i n e , CH C1 , -78°. e) Table I s o l v e n t s , r e f l u x , f ) 2a i s monomeric i n s o l u t i o n , but c r y s t a l l i z a t i o n produces Ph3 PO PPh "(OTf)2 ( 9 ) . 2

2

2

+

2

2

2

2

2

+

3

A v a r i e t y of the s a l t s , 3a, were prepared i n s o l u t i o n and charac t e r i z e d by proton nmr (these were v i r t u a l l y p r e d i c t a b l e using normal values of J p _ ) and proton decoupled P nmr. The f o l l o w i n g were prepared i n s o l u t i o n , with Ρ chemical s h i f t s i n paren t h e s i s : R=CH (64.0), R=CH CF (68), R=CH(CH ) (59.4), R = ( C H ) C H C H C H (61.7), R=(CH ) CCH CH (61.6), c y c l o h e x y l (59.2), benzyl (60.6), o c t y l (60.87) C1CH CH 0CH CH (62.8), C H (65.6) . The l a s t was i s o l a t e d as a c r y s t a l l i n e s o l i d , and f u r t h e r charac t e r i z e d : Mp 171°, F nmr s i n g l e t , +2.4 ppm r e l a t i v e to CF C00D, the high r e s o l u t i o n mass spectrum showed the i n t a c t c a t i o n . The y i e l d s of the s a l t s depend upon the s o l v e n t ; r i g o r o u s l y d r i e d CH Cl2 and CH CN give near q u a n t i t a t i v e y i e l d s , THF much lower y i e l d s (even a t -78°) to suppress the t r i f l i c anhydride THF r e a c t i o n ) , and l i q u i d S 0 y i e l d s no d e t e c t a b l e product. 3 1

H

3

1

2

3

2

3

3

2

2

3

2

3

2

2

2

2

2

6

5

1 9

3

2

3

2


2

31.

H A M ρ A N D LEWIS

Alkylation

by A Ikoxyphosponium

159

Salts

Toward i o d i d e , bromide and thiocyanate ions the phosphonium s a l t s reacted t o give a l k y l a t e d products i n f a i r y i e l d s . Yields, based on s t a r t i n g t r i f l i c anhydride which was allowed t o r e a c t with a s l i g h t excess o f phosphine oxide, are given i n Table I . Table I Y i e l d s o f ROPPhtOTf~+ Nu" -> RNu R e a c t i o n


R

solvent*

1-octyl

THF CH CN THF

If

3

3

Nu

product(yield)

LiBr

RBr

It

II

3

II

2-(2-chloroethoxy)ethyl 3,3-dimethylbutyl 3-methylbutyl isopropyl tertbutyl 1-octyl 1-cyclohexyl

CH C1 2

2

CH C12 2

CH C1 CDC1 CDCI3 CH CN CHCI3 2

3

3

2

LiCl

RC1

LiBr NMe^Br Nal Nal Nal KSCN° Et NCH PhCl

RBr RBr RI RI

3

2

R I

d RSCN RC1

(71) (61) ( 5) (55) (43) (70) (42) (52) (87) (0)

a) Y i e l d s are based on T f 0 and are determined by gc with an i n t e r n a l standard, b) T h i s i s the solvent used i n the second step i n Scheme 1, the solvent f o r the f i r s t step was sometimes l e f t , sometimes removed. c) 18-crown-6 was used i n t h i s experiment, but i t s f u n c t i o n was not explored. d) No RNCS was seen i n the gc traces. 2

Some other r e a c t i o n courses were a l s o seen. For example, 3a, R=octyl with b u t y l l i t h i u m gave no s i g n i f i c a n t y i e l d o f dodecane. The P chemical s h i f t o f an important component suggested an y l i d e , perhaps derived from butyltriphenylphosphonium from a t t a c k at Ρ r a t h e r than C. E t h y l magnesium bromide with 3a, R=octyl gave mostly 1-bromooctane, but with butylmagnesium c h l o r i d e , about 20% y i e l d of dodecane was observed with no 1-chlorooctane. The polymer bound triphenylphosphine oxide was synthesized using e s t a b l i s h e d techniques from a macro r e t i c u l a r DVB/styrene copolymer, Amberlite XE-305 (10). The phosphorus content was determined g r a v i m e t r i c a l l y using the K j e l d a h l method (11). Various polymers contained between 30 and 50% o f the aromatic rings f u n c t i o n a l i z e d . Reactions o f the bound alkoxyphosphonium t r i f l a t e (formed i n an i d e n t i c a l manner to that of the unbound analog 3a), with the n u c l e o p h i l e s shown i n Table I I were followed by i r and the y i e l d s determined by gc. Our few p r e l i m i n a r y r e s u l t s demonstrate that t h e i r a l k y l a t i n g a b i l i t i e s are comparable t o that o f the unanchored alkoxyphosphoniums. The triphenylphosphine oxide polymer produced can be r e c y c l e d back t o the d i t r i f l a t e , with t r i f l i c anhydride. 3 1


160

PHOSPHORUS CHEMISTRY

Table I I

+ P0L-P(0R)Ph + Nu


2

+

P0L-P(0)Ph + NuR 2

R

solvent

Nu

product(yield)

3-methylbutyl 1-octyl 2-phenylethyl 2-(2-ehloroethoxy) ethyl

CH C1 CH CN CH CN 3

Nal LiBr LiBr

RBr RBr RBr

(60) (60) (52)

CH CN HMPA

LiBr LiBr

RBr RBr

(20) (0)

tt

2

3

3

Acknowledgement : Support o f t h i s work by theRobert A. Welch Foundation i s g r a t e f u l l y acknowledged.

Literature Cited

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Landauer, S. R.; Rydon, H. N. J. Chem. Soc. 1953, 2224. Castro, B.; Selve, C. Bull. Soc. Chim. Fr. 1971, 12, 4368-4372. Appel, R. Angew. Chem. Int. Ed. Engl. 1975, 14, 801-811. Hendrickson, J. B.; Schwartzman, S. M. Tet. Lett. 1975, 4, 277-280. Lewis, E. S.; Walker, B. J.; Ziurys, L. M. Chem. Comm. 1978, 424-425. Arshady, R.; Kenner, V. W. J. Poly. Sci. Poly. Ed. 1974, 12, 2017-2025. U. S. patent 3,375,304, 1968; Chem. Abst. 1968, 68, 965595. Schwartzman, S. M. Ph.D. thesis, 1975, Brandeis University. Aaberg, B.; Gramstad, Τ.' Husebye, S. Tet. Lett. 1979, 24, Delles, H. W.; Schwarz, R. W. J. Am. Chem. Soc. 1974, 96, 6469-6480. Steyermark, A. "Quantitative Organic Microanalysis 2nd Ed." 1961, New York, Academic Press; p 354.

RECEIVED June 30, 1981.


Alkylation by Way of Monomeric and Polymeric Alkoxyphosphonium

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