Kov. 5 , 19Gl
'y-ELIhIINATION O F
4423
QUATERR'ARY AMMONIUM COMPOUNDS
Compound VI, m.p. 118-120" dec., was obtained in essenat 187" using a 10 ft. X 0.25-in. column packed with Carbotially quantitative yield. wax 20 M on Chromosorb in a ratio of 1:3 indicated t h a t the 1,l-diphenylcyclopropanewas homogeneous. Anal. Calcd. for CZ4H&JBr: iY,3.41. Found: N, 3.26. Reaction of 3-Phenylpropylbenzyldimethylammonium From reaction of 14.8 g. of compound V with 0.06 mole of Bromide (V) with Sodium Amide.-An equimolar mixture of sodium amide in 200 ml , of liquid ammonia for 4 hr ., 0.90 g
.
3-phenylpropyldimethylamine'7 and benzyl bromide in dry (13%) of a mixture of 1,l-diphenylpropene and 1,l-diphenylbenzene was refluxed 48 hr. and gave quantitatively corn- cyclopropane, b.p. 93-97' (1 mm.), nZ0D 1.5958, was isopound V, m.p. 153-154", unchanged on recrystallization lated. The n.m.r. spectrum showed signals at 233 C . P . S . ~ ~ from alcohol. (cyclopropyl), 217 and 209 C.P.S. (methyl), 47 C.P.S. (vinyl) Anal. Calcd. for C18H&Br: C, 64.67; H , i.24; N, and -7 C.P.S. (phenyl). Analysis of the infrared spectrum using bands at 970 cm.-l (characteristic of 1,l-diphenyl4.19. Found: C,64.86; H , 7 . 3 8 ; S , 4 . 1 4 . propene30) and 936 cm.-l (characteristic of 1,l-diphenylTreatment of 28.5 g. of compound L' with 0.15 mole of cyclopropane) indicated t h a t the mixture consisted of 687, sodium amide in 200 ml. of liquid ammonia for 4 hr. in a of 1,l-diphenylpropene and 32y0 of 1, l-diphenylcyclopromanner similar t o that described above yielded 2.90 g. pane. The composition according to gas phase chromato(25%) of phenylpropene, b.p. 86" (36 mm.) n Z 71.5400. ~ graphic analysis was 64y0 1,l-diphenylpropene and 36y0 1,lThe infrared spectrum was essentially the same as that of diphenylcyclopropane. A minor constituent, probably 3,3phenylpropene (largely trans-1-phenylpropene) prepared by Hofmann degradation of 3-phenylpropyldiniethylamine.~~ diphenylpropene, also was detected. Chromatography was as described above in the analysis of 1,l-diphenylThe n.m.r. spectrum had peaks a t 2192Gand 213 C.P.S. performed cyclopropane from compound IV. (methyl), 47 C.P.S. (vinyl) and 1 c.p.s. (phenyl). IlistillaThe basic fraction on distillation gave 1.2 g. (257,) of tion of the basic fraction separated 4.27 g. (327,) of benzyldimethylamine, b.p. 92-94" (16 mm.), identified by its in- benzyldimethylamine, b.p. 83.5-84' (34 mm.), identified frared spectrum, and 8.10 g. ( 3 % 7 Gof) a mixture of amines, by its infrared spectrum, and a dark residue. This residue, b.p. 131-134' (1.2 mm.), n% 1.5484, resulting from Soin- when heated at 160-180" at 0.5 mm. in a short-path distillation apparatus, yielded 1.56 g. of a viscous yellow oil which melet rearrangetnent.l9 probably represents the amines resulting from Sommelet Anal. Calcd. for ClsH23K: C , 85.32; H, 9.15; N, 5 . 5 3 . rearrangement (see above). The amount of compound VI Found: C, 85.56; H, 9.43; N, 5.65. recovered was 3.3 g. (2275). Acknowledgments.-I wish to thank K r s . CaroThe amount of compound V recovered was 4.8 g. (17yG). Reaction of 3,3-Diphenylpropylbenzyldimethylammo- lyn Haney for the n.m.r. spectra, Dr. K . S. Mcnium Bromide (VI) with Sodium Amide.-3,3-DiphenylproCallum for the quantitative infrared analysis, and pyldimethylamineZi in dry benzene was reflused with a n Xrs. Janice Lane and Mr. Kirt Keller for technical equivalent weight of benzyl bromide for 1.5 hr. and the reassistance. sulting mixture was stirred a t rooin temperature for 21 hr.
[CONTRIBUTION FROM
THE
GORGASLABORATORY OF THE ROHM& HAASCo , REDSTONE ARSENALRESEARCH DIVISION, HUNTSVILLE, 4LA.]
Elimination Reactions. 11. Some Electronic and Steric Effects in 7-Elimination Reactions of Quaternary Ammonium Compounds' BY CARLL. BUMGARDNER RECEIVEDAPRIL 21, 1981 Pyrolysis of 3,3-diphenylpropyldimethylamineoxide (111) gives 3,3-diphenylpropene, but thermal decomposition of 3,3diphenylpropyltrimethylammonium hydroxide (IT') yields a mixture consisting of approximately 727, of 1,l-diphenylpropene and 28% of 1,l-diphenylcyclopropaneaccording to gas phase chromatography, Treatment of 3-o-tolylpropyltrimethylammonium iodide ( Y I I ) with sodium amide in liquid ammonia gives o-tolylcyclopropane Under the same conditions, 3mesitylpropyldimethylammonium iodide ( Y I I I ) fails t o react. The latter compound, when allowed t o react with potassium amide in liquid ammonia, gives 1-mesitylpropene. These and similar reactions are discussed in terms of the stereoelectronic requirements of ?-elimination.
In the first paper of this series? the reaction of certain y-arylpropyl quaternary ammonium halides with sodium amide in liquid ammonia was reported to yield cyclopropane derivates (y-elimination) instead of olefins (&elimination). To study some stereoelectronic requirements of y-elimination, we have synthesized several compounds having in common the skeleton shown and eliminated the amine function by several methods. \
Y
P
,c-c-c--s I
1
H
H
4 +-
!
The ratio of /3- to y-elimination products was studied as a function of y-carbon environment and the nature of the attacking base. (1) Sponsored b y t h e U. S. Army Ordnance Corps, Contract D A 01-021-ORD-11878. A portion of this work was presented a t t h e 137th Meeting of t h e American Chemical Society, Cleveland, 0 , April, 1960. (2) C . L. Bumgardner, J . Ani. Chem. Sor , 83, 4420 (1961).
3-Phenylpropylbenzyldimethylammonium bromide (I) and sodium amide in liquid ammonia give 1-phenylpropene as the major elimination product. Under the same conditions, 3,3-diphenylpropylbenzyldiinethylammonium bromide (11) yields a mixture of 1,I-diphenylpropene and 1,l-diphenylcyclopropane. C ~ H S H ~ C H ~ C HCH3)?Br Z&( --f CsHjCH=CHCH3
I
CHzCsH5 t
-
-
(CbH5)2CHCHXH2N(CH3)2Br
(CeH,),C=CHCH,
The difference in elimination products, which was attributed to additional activation by the second y-phenyl group, suggested that other elimination
CARLL. BUMGARDNER
4424
methods, such as amine oxide and Hofmann reactions, might be similarly affected by substitution on the y-carbon atom. 3-Phenylpropyldimethylamine oxide (compound V) is known to give the uncon jugated olefin, 3-phenylpropene, upon thermal decomposition; 3-phenylpropyltrimethylammonium hydroxide (compound VI) is known to yield mainly the conjugated olefin, l-phenylpro~ e n e . 3,3-Diphenylpropyldimethylamine ~ oxide (111) and 3,3-diphenylpropyltrimethylammonium hydroxide (IV) therefore were prepared and pyro lyzed. (CsH&CHCHzCHzk( C H S ) ~ ( C ~ H ~ ) ~ C H C H Z C HCH3)a ~;(
I
111
OH
IV
-0
Vol. 83
when a concentrated aqueous solution of I V was heated from SO to 150" a t 2 mm. Gas phase chromatography indicated that the mixture consisted of approximately 72% of the olefin and 28% of the cyclopropane derivative, a composition close to that obtained from quaternary bromide I1 and sodium amide in liquid ammonia.2 These results are compared in Table I. To see if 7-elimination might be sensitive to substituents in the o-position of aryl groups attached to the y-carbon atom, 3-o-tolylpropyltrimethyl ammonium iodide (VII) and 3-mesitylpropyltrimethylammonium iodide (VIII) were prepared and allowed to react with sodium amide in liquid ammonia. Under these conditions 3-phenylpropyltrimethylammonium iodide (IX) undergoes y-elimination exclusively giving phenylcyclopropane in high yield
Amine oxide (111) was obtained by treating 3,3diphenylpropyldimethylamine with aqueous %yo hydrogen peroxide solution in the usual manner. CH, Methylation of 3,3-diphenylpropyldimethylamine with methyl iodide followed by treatment of the fl' -." ~ - C H , C H , ~ H , $ I C H \ 3 methiodide with silver oxide gave quaternary 1hydroxide IV. 3,3-Diphenylpropyldimethylamine was synthesized from P,P-diphenylpropionic acid \'I1 C : i , ~ ~ ; i z C H z C 1-~ z ~ ~ C H 3 ~ ~ by steps similar to those used for conversion of cyclopentanecarboxylic acid to cyclopentylmethyl+ CH3 dimethylamine.* ~d I':-cH,CH,CH,~K(CH~)~ VI11 Heating amine oxide 111 from 80 to 180' under 1reduced pressure produced 3,3-diphenylpropene in IS 70y0yield. Methiodides VI1 and VI11 were obtained by treatI11 +(CeH6)2CHCH=CH2 Infrared, ultraviolet and n.m.r. spectra indicated ing the respective tertiary amines 3-o-tolylpropyland 3-mesitylpropyldimethylamine that neither the conjugated olefin nor the cyclo- dimethylamine with methyl iodide. These amines were synthepropyl isomer was present in the product. Thermal decomposition of quaternary hydroxide sized by steps similar to those outlined above for preparation of 3,3-diphenylpropyldimethylamine. IV, though, gave different results. From methiodide l r I I and sodium amide in liquid ammonia o-tolylcyclopropane was obtained in IV (C,H,)zC=CHCH, 87% yield. This structural assignment is based on analysis of the n.m.r., infrared, and ultraviolet C.& spectra (see Expt.). Gas phase chromatography A mixture of 1,l-diphenylpropene and 1,l-di- indicated that the product was homogeneous. phenylcyclopropane was obtained in 7270 yield _i
c6Hx
__t
TABLE I ELIMINATIOX REACTIONS OF
,+ (1)
R
CSHj Compound I
I1 I11
IV V VI a
olefin
)ccH~cH,~(cH~)~(a)
I
H
I
\+ cyclopropane
R'
N a t u r e of R ' s Base R = H h'aNHz R' = CsHnCHz ("3) h-ahTHI R = C6H6 R' = C B H ~ C H I ("3) R = CeHs Amine R' = 0Oxide R = CsHs OH R' = CHa (Hofmann) R = H Amine R' = 0Oxide R = H OHR' = CHa (Hofmann)
Ref. 2.
-
b
Elimination route (1)
deriv.
Type of olefin Conjugateda
(1) and (2) Conjugated" (1)
(1) and (2)
Unconjugated Conjugated
(1)
Unconjugatedb
(1)
Conjugatedb
Ref. 3.
(3) A. C. Cope a n d C. L. Bumgardner, J. A m . Chem. SOC.,79, 960 (1957). (4) A. C. Cope, C. L. Bumgardner and E. E. Schweizer, { b i d . , 79, 4729 (1957).
No reaction product was detected when methiodide VI11 was subjected to sodium amide in liquid ammonia for 4 hr., and the starting material was recovered in high yield. Some decomposition did take place when methiodide VI11 was allowed to react with potassiuni amide in liquid ammonia, and trans-1-mesitylpropene, characterized by its ultraviolet and n.m.r. spectra, was isolated in 29% yield after 4 hr. Gas phase chromatography indicated that two other (probably isomeric) cornpounds were present in trace quantities. These results are collected in Table 11.
Discussion Table I shows that amine oxides I11 and V react by the same route, although the former compound contains two y-phenyl groups. In contrast, quaternary bromides I and I1 react by different paths. The process by which olefins are formed from amine oxides is viewed as an intramolecular @-elimination
7-ELIMINATION OF QUATERNARY AMMONIUM COMPOUNDS
Nov. 5 , 1961
4425
I n the latter reaction, elimination still might be concerted, but the transition state would have considerable carbanion character.’ The pyrolysis of compound IV seems to be the f i ~ R ~ H , - I H z - c H ~ - i -t rCHr.I first case of a hydrocarbon-substituted quaternary ammonium hydroxide giving rise to a cyclopropane R derivative.* deriv. Some time ago, W e i n s t ~ c kin , ~ considering some ComBase Elimination Yield, anomalous Hofmann reactions, suggested that the (in NII?) route % pound Nature of R’s product obtained by Ingold and Rogers’O from deVI1 R’ = CH3 NaNHz (2) 87 composition of 3,3-dicarbethoxy-4-phenylbutyltriR = H methylammonium ethoxide was l-benzyl-l-car.. VI11 R = R’ = CHI NaNHz No reacn. bethoxycyclopropane and not an olefinic isomer as VI11 R R’= CH3 KNHz (1) 29 originally proposed. W-einstock considered that IX R = R’ = H NaNHs (2) 80“ the cyclopropyl compound could be produced by Ref. 2. displacement of trimethylamine by the stable carinvolving a five-membered cyclic transition state.5 banion generated y to the nitrogen atom. Apparently in the decomposition of amine oxide 111, the five-membered cyclic state still is preferred over other pathways involving intra- or intermolecular abstraction of the acidic y-hydrogen atom. TABLE 11 ELIMINATION REACTIONS OF
/ (CSHS),CHCH=CH,
The fact that the unconjugated olefin is obtained exclusively is another example of the mildness and utility of the amine oxide procedure.3 The Hofmann route to olefins normally involves concerted removal of a @-hydrogen atom by hydroxide ion and displacement of trimethylamine by the electron pair forming the double bond.5 In some base-catalyzed elimination reactions, however, evidence for a @-carbanionintermediate has been obtained.6 Occurrence of both /3- and y-elimination during pyrolysis of quaternary hydroxide IV indicates that both concerted and y-carbanion pathways are available, which lead to olefin and a cyclopropane derivative, respectively. LsH5
CsHs’
4 =--A& \CHCHCH,N (CH,)
I) , -f H
+
( ( G Hj),CHCH= CH,]
1
(C6H5)2C=CHCH3
OH
OH
Subsequently, Rogerssb presented evidence that the product is the cyclopropane derivative but preferred to formulate the conversion as an intramolecular ring closure synchronized with decarboxylation. The latter author assigned a special function to the carboxyl group to explain why a cyclopropane ring is formed in the above case and in a similar one,8abut not in the Hofmann degradation of quaternary hydroxide VI. 1Vhereas Rogers’ mechanism may function in some cases, formation of substantial amounts of 1,l-diphenylcyclopropane from quaternary hydroxide IV shows that decarboxylation is not essential. And although no phenylcyclopropane is obtained from thermal decomposition of 3-phenylpropyltrimethylammonium hydroxide (VI), treatment of 3-phenylpropyltrimethylammonlium iodide with the stronger base, sodium amide in liquid ammonia, does produce the cyclopropyl compound in high yield.2 Apparently, y-elimination may become important when acid-base relationships are such that appreciable negative charge may be generated on the y-carbon atom. The y-eliminations considered above and previously2 may be considered as a special class of Elcb where the conjugate base is in the y-position or, possibly, as an E2 elimination in which the transition state has y-carbanion character. Table I1 shows that the single o-methyl group present in methiodide VI1 does not interfere with the y-elimination process. Methiodide VIII, however, which has two ortho substituents flanking the y-carbon atom, fails to undergo either y- or 0(7) For a possible example of a concerted p-elimination reaction which has carbanion character see E. D. Hughes and J. C. Maynard,
J. Chem. Soc., 4087 (1960). (5) A. C. Cope and E. R. Trumbull, “Organic Reactions,” Vol 11, ed. by A. C. Cope, John Wiley and Sons, Inc., New York, N. Y . , 1960, p. 317. (6) (a) 0 B. Ramsay and J. Hine, Abstracts of Papers, Southeastern Regional Meeting of t h e American Chemical Society, Birmingham, Ala., Xovember 3-5, 1960, p. 2 4 ; (b) J. Weinstock and F. G. Bordwell, J. A m . Chem. Soc., 77, 6706 (1955); (c) D. J. Cram, F. D. Greene and C. H. De Puy, i b i d . , 78, 790 (1956).
(8) Several examples are known where malonic ester-substituted quaternary ammonium salts give cyclopropanes on treatment with hydroxide or alkoxide: (a) H. Rinderknecht and C. Nieman, J . A m . Chem. SOL.,7 3 , 4259 (1951); (b) M. A. T. Rogers, J. &E. Chem., 22, 350 (1957). A related case is the pyrolysis of 1-methyl-3-diethylaminoethyloxindole methiodide which yields l-methyl-spiro-3,3cyclopropyloxindole; J. C. Seaton and L. Marion, Can. J . Chcm., 36, 1101 (1957). (9) J. Weinstock, J. Org. C h o n . , 21, 540 (1958). (10) C. K. Ingold and M. A. T. Rogers, J . Chcm. SOC.,722 (1935).
TABLE 111 AMINESPREPARED F R O M CARBOXYLIC . ~ D Dimethylamine
'C.
n.p. RIm.
Yield, iI:qD
3-Mesitylpropyl77-78 0.5 1.5072 3-o-Tolylpropyl63-64 2 1.t5034 3,3-Diphenylpropyl- 4 3 , 5 4 4 ,Sa a M.P.; N. Sperber, M. Stierlock and D. Papa,
;;, (
Formilla
--Carhon Calcc!.
S
--I:,,un? c;
77 CIIH,,S 51.89 81.62 73 C12HjYS 8 1 . 3 0 81.84 57 J . A v t . Chc7?7. S o c . , 75, 1122 (1953).
- H y d i - o g ~ n , ";
--
S i t r t l g e n .
