MICHAEL ADDITION OF ETHYL (X-CYANOBUTYRATE TO BENZENE ANALOGUES OF CHALKONES

S.ToMA Department oj Organic Chemistry, Komensky University, Bratislava

2771

Received July 22nd, 1968

The addition of ethy11X-cyanobutyrate to chalkones is a first order reaction with respect to chal­kone. log k can be well correlated with a constants. In the studied temperature range (25 - 45°C) Q

does not depend on temperature. The a constants for ferrocenyl were determined: aa, = - 0'582, up = -0'155 and am = - 0,002. 2-Fur~1 and 2-thienyl manifested themselves differently, depending on whether they were bound to a carbonyl group carbon (aa, = 0,104, or - 0'058) or to the l3-carbon of the double bond (aa, = -0'225, or - 0 '146). We calculated the coefficient of the transfer through the double bond (/I = 0'641). The substitution of the phenyl group by ferrocenyl causes a substantial diminution of the sensitivity of the reaction to the influence of the substituent.

Ingold t proposed a mechanism for the Michael reaction in which he supposed that the rate determining stage is the attack of the anion of the reagent on . the 13 carbon atom of the multiple bond. These opinions of Ingold were confirmed in several papers2 - 5. It was further established that the Michael addition is a first order re­action with respect to the substrate (unsaturated compounds)6,7 and it was also proved that the log k in the addition of ethyl cyanoacetate to ferrocenc analogues of chalkone can be correlated with Hammett's ()' constants8

•

In this study we carried out kinetic measurements of the addition of ethyl o:-cyano­butyrate to benzene and ferrocene analogues of chalkones.

EXPERIMENTAL

Chemicals

All benzene analogues of chalkone were prepared by base catalysed aldol condensation of corres­ponding aldehydes and ketones according t09

. Ferrocene analogues of chalk ones were also pre­pared by base catalysed aldol condensation according to10,11. Chalkones were purified by repeat-

Collection Czechoslov. Chem. Commun. IVol. 341 (1969)

2772 Toma:

ed crystallization from ethanol, and the purity was controlled by elemental analysis, thin-layer chromatography and comparison with literature data. Melting points of chalkones and literature references are listed in Tables I - III. Ethyl Cl-cyanobutyrate was prepared analogously to ethyl cyanoacetate12

, its boiling point coincided with that from the literature13 • The purity was also controlled by elemental analysis.

Apparatus and Measurement Methods

All measurements were carried out on a spectrophotometer Spektromon 201 (MOM, Budapest; with a prism). The spectra were measured in 4. 10 - 5M methanollc solutions. Methanol was of the p.a. purity, purchased from Lachema. The spectrum of ethyl Cl-cyanobutyrate in methanol in the absence of catalyst did not display any maximum in the region above 220 nm. After the addition of the catalyst a maximum appeared at 245 nm, the log e of which depended on concentration. At an ethyl Cl-cyanoacetate concentration of 1'6 . 10- 2M and sodium methoxide concentra tion of 5·6 . 10- 3 M log e = I '96; at an ethyl Cl-cyanobutyra te concentration 0' 8 . 10- 2M and sodium methoxide concentration 2·8. 10- 3M log e = 1·86. We have checked further the validi ty of Lam­bert-Beer's law at the Amax of chalkone and in the given concentration range, and also whether the character of the spectrum of chalkone does not change in the neighbourhood of the maximum.

Kinetic measurements were carried out in methanol (dried over sodium, b.p. 65·5°C). Concen­tration of chalkone was 4 . 10- 5

M, of ethyl Cl-cyanobutyrate 4. 10 - 2 M and of sodium me tho xi de 1'4 . 10- 3M . The reaction was carried out at the following temperatures: 25, 30, 35, 40 and 45°C

TABLE I

Reaction of Chalkones of the Type ArCH= CH- CO - C6H5 with Ethyl Cl-Cyanobutyrate

No

4

10 11 12 13 14 15

p-N(CH 3h p-NH 2 p-OCH 3 p-CH 3 H p-F p -Cl m-Cl p-CN m-N02 p-Fc m-Fc

Ar = 2-thienyl Ar = 2-furyl Ar = Fc

nm

420 397 340 320 308 310 312 299 302 290 347 286 338 342 325

a Refers only to melting points

log e

4·47 4·39 4'42 4'42 4·36 4'39 4·46 4·34 4'56 4'39 4'39 4'34 4·35 4·45 4·21

10 3 . k, min- 1

25°C 30°C 35c C

7·9 ± 0·7 10'1 ± 0·2 16'4 ± 0·3 7' 1 ± 0'2 10·6 ± 0'2 16·0 ± 0·4

16'4 ± 1'4 23'6 ± 0'5 33-6 ± 1·5 20·9 ± 0·8 31'6 ± 0·8 39·5 ± 2·0 27'9 ± 0·3 41'5 ± 0'3 51' 7 ± 2·2 41 ± 2·8 59·2 ± 0·2 66·6 ± 4·8 60'2 ± 2'8 83·2 ± 2·4 ION ± 10 64'5 ± 5-8 91·6 ± 4-6 118·6 ± 8

196 ± 5·3 298 :± 5 425 ± 18 231 ± 1 326 ± 7 357 ± 5

22·6 ± 0·8 30'45 ± 0'2 43·7 ± 0·9 32'5 ± 2'5 47·7 ± 1·6 62'4 ± 0'8 26'3 ± 0'8 34' 1 ± 2'2 43·9 ± 3·1 19'3 ± 0'2 25·8 ± I-4 35·8 ± 2'5

6·93 ± 0'2 II·31 ± 0·4 17-9 ± 0'3

Collection Czechoslov. Chern. Commun. /Vo\. 34 / (1969)

Michael Addition of Ethyl cx-Cyanobutyrate 2773

(Ultrathermostat; accuracy 0-1 °C)_ The course of the reaction was followed by the measurement of the decrease in the absorbance of the 2 maximum of chalkone in samples withdrawn from the reaction mixture at suitable time intervals_ The wave-lengths of maxima of chalkones at which the measurements were carried out, together with log e and the calculated rate constants are given in Tables I - III. In these tables the calculated values for activation energy and activation entropy of the studied reactions are also presented_

RESULTS AND DISCUSSION

Additions of ethyl ex-cyanobutyrate were carried out with chalkones of the following types: C6 HsCOCH=CHC6 H4 (X) (type A), (X)C6 H 4 COCH=CHC6H s (type B), FcCOCH=CHC6H 4 (X) (type C), (X)C6H 4 COCH=CHFc (type D), Fc = ferrocenyl (C1oHgFe)- In order to make sure that in this case too the reaction is of the first order with respect to chalkone, we carried out the addition of ethyl ex-cyanobutyrate to unsubstituted chalkone at the following concentrations; 4 _ 1O- 4 M; 2 _ 10-4

;'1;

4 _ 10- sM_ We found that the half-time of the reaction is independent of the starting concentration of chalkone (tl/2 = 20-1 ± 1 min; 19-4 ± 0-8 min; 18-8 ± 0-8 min) and hence that the reaction is of the first order. As we did not isolate the products

TABLE I

(continued)

E - LlS* M_p_ Ref. a

40°C 45°C kcal mol- 1 cal mol-'1 grad - 1 °C

22-2 ± I-I 34-3 ± 3-5 14-7 ± 1-4 29-1 ± 0-2 114 14 2N± 0-6 30-9 ± 0-4 13-9 ± 0-4 31 -9 ± 0-1 151 15 45-9 ± 2-0 62-2 ± 0-6 12-5 ± 0-1 34-9 ± 0-7 77 16 53-3 ± 0-9 74-7 ± 2-2 11 -5 ± 0-6 37-7 ± 0-1 97 17 74-3 ± 2 97-9 ± I-I 11-6 ± 0-6 36-9 ± 0-1 56 18

105-2 ± 1-4 140-3 ± 11-4 ± 1-0 36-9 ± 0-1 88 19 137-6 ± 9 204 ± 11-6 ± 0-4 35-5 ± 0-1 114 15 173 ± 6 221 ± 11-6 ± 0-9 35-3 ± 0-1 75 20 515 ± 23 723 ± 42 11-9 ± 0-7 32-1 ± 0-1 156 21 927 ± 4 822 ± 59 11-3 ± 1-4 33-9 ± 0-2 148 15

59-I ± 3 75-1 ± 1-2 11-5 ± 0-3 37-1 ± 0-1 135 - 138 11 78-9 ± 6-9 104 ± 4-4 10-7 ± 0-1 39-5 ± 0-1 150- 153 It 57-8 ± 3-5 72-5 ± 4-7 9-6 ± 0-8 34-5 ± 0-3 57 23 60-8 ± 1-2 66-9 ± 9-2 11-9 ± 0-3 36-8 ± 0-1 37 24 27-2 ± 0-5 41-9± 16-7 ± 0-7 22-5 ± 0-1 135 22

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2774 Toma:

of the addition and could not determine A ", Guggenheim's method29 was used for the calculation of rate constant, which is suitable for such reactions3 o. Logarithms of the calculated rate constants were correlated with (J' constants31

. Working up the results according to Jaffee32 gave for chalkones of the type A the results given in Table IV. These results were obtained when the value for p-dimethylamino derivative was not taken into account. If the (J'-value according to Jaffee ((J'p = -0'600) was taken for it, we obtained at 25°C e = 1'091, r = 0'991, Sq = ,0'051 and S = 0'072, and at 45°C e = 1'032, r = 0'983, sa = 0·067 and s = 0,095;-these results are very close to those given above (Fig. 1).

In the case of chalkones of the type B the results given in Table IV were obtained . For the computation of the above given values we did not take for corrdation p-dimethylamino derivative and m-methoxy derivative (points No 1 and 7 in Fig. 2). If both these derivatives were taken for correlation, but for p-dimethylamino deriv­ative the value (J' = -0.60032 was employed, we obtained at the temperature 25°C e = 1'690, r = 0'996, sa = 0·043 and s = 0'066, and at 45°C e = 1· 622, r = O' 995

TABLE n Reaction of Chalkones of the Type ArCO-CH= CH--C6 Hs with Ethyl IX-Cyanobutyrate

No

4

10 11

12 13 14 15 16 17 18

p-N(CH3)2

p -NH2 p-OCH3 p-CH3 H p-F m-OCH 3 p-CI p-Br m-CI m-Br m-N0 2

p-N0 2

p-Fc m-Fc

Ar = 2-thienyl Ar = 2-fury\ Ar= Fc

11m

390 367 319 308 308 308 308 310 310 312 310 315 318 325 307 322 320 306

a Refers only to melting points.

103 • k , min- 1

log e ------.~-----------~~-----

25°C 30°C 35°C

4'41 z.s ± 0·4 3-6 ± 0·4 309+ 0'1 4·30 2'5 ± 0·3 3'2 ± 0'2 3·6 ± 0'1 4'51 8'6 ± 0·3 12'1 ± 0·0 16·2 ± 4-39 17-4 ± 0'3 20'4 ± 31·2 ± 0·0 4·36 27·9 ± 0·3 41·5 ± 5·6 51'7 ± 2'2 4·42 4O'2 ± 2'5 49 ± 6'2 70'5 ± 2'9 4'40 32-4 ± 4·6 42-2 ± 4·6 59·2 ± 2'9 4'42 71·3 ± 2·3 104-8 ± 1O 141 ± 6 4'34 84-4 ± 1·3 108·6 ± 1 154 ± 4·25 107-8 ± 6 147 ± 1 189 ± 4' 33 126· ± 8 167 ±6 118 ± 12 4'34 465 ± 14 655 ± 1l 791 ± 27 4'30 690 ± 9 838 ± 9 1074 ± 37 4' 34 17·3 ± 0·9 22·86 ± 0'5 31'1 ± 1·5 4'47 33'7 ± 1'8 41'2 ± 1,2 54'9 ± 1'1 4'49 24·9 ± 0'7 32 ± 0'4 42'5 ± 0·6 4·48 44-8 ± 0·9 65-3 ± 5·7 77-6 ± 1-4

4'35 3'1 ± 0'1 4'2 ± 0'1 6'0 ± 0'2

Collection Czechoslov. Chern. Comrnun. IVol. 341 (1969)

Michael Addition ~f Ethyl cx-Cyanobutyrate 2775

SQ = 0·050 and S = 0·076. These values are close to the above mentioned. In all instances the correlation is good.

In the case of ferrocene analogues of chalkones the measurements were carried om only at 45°C. The following values were obtained for chalkones of the type C and D respectively: C - (} = 0'673, r = 0'877, s(1 = 0·102 and s = 0'102; D - (! = = 1'383, r = 0'946, sl! = 0·328 and S = 0·368 (Fig. 3). The correlation is worse than in the case of benzene derivatives, because the reactions are slower and they proceed rapidly toward the equilibrium, so that our readings were relatively less accurate. In both types of ferrocene analogues of chalkones the sensitivity of the reaction to the influence of the substituents is rather decreased. This is caused by the ferrocenyl group which by its electron-donor effect saturates the electron-acceptor property of the carbonyl group, so that the influence of other substituents cannot manifest itself to a great extent.

The values given in Table IV were utilized for the calculation of the coefficient of transfer through the double bond. We obtained the value 11 = 0·641 ± 0'016,

TABLE II

(continued)

E -~S* M.p. Ref." • __ 0 _ ________ ______

kcal. mol-' l cal mol-- 1 grad -1 °C 40°C 45°C

4-9 ± 0·3 9'1 ± 0'1 10'1 ± 2'1 46'6 ± 0'7 165 25 5·7 ± 0'2 9·9 ± 0·3 12-4 ± 2'1 39'4 ± 0·3 108 20

22'9 ± 0·8 30'3 ± 2'6 11-8 ± 0'1 38'6 ± 0'1 105 26 42-3 ± 0'1 58-4 ± 0·4 11·8 ± 0·8 37·3 ± 0'1 59 26 74·3 ± 97'9 ± 1'1 11 ·6 ± 1'5 36'9 ± 0' 1 56 18 93'9 ± 1·9 135 ± 6'5 11'5 ± 0'7 36'6 ± 0·1 78 27 79- 1 ± 0·1 107 ± 0'1 11 ·1 ± 0'5 38·4 ± 0·0 44 27

189'3 ± 1 258·4 ± 2·4 11 '9 ± 0'3 34'1 ± 0'1 97 20 186 ± 2'3 270 ± 17 10·7 ± 0'5 37-6 ± 0'1 104 20 258 ± 221 ± 8 10'5 ± 0'2 37-9 ± 0'1 94 27 272 ± 4 412 ± 6 10'S ± 0'8 37·6 ± 0·1 95 20 964 ± 58 1395 ± 58 9-6 ± 1·0 38' 1 ± 0·1 129 20

1328 ±1O 1890 ± 128 9'3 ± 0'1 38'4 ± 0'1 146 20 40·9 ± 2·6 52-4 ± 1'5 10'9 ± 1-1 39·9 ± 0'2 175-178 11 73·1 ± 1'4 97'1 ± 2·6 10'1 ± 0·4 41'7 ± 0·1 166- 168 11 55·6 ± 2·3 10'6 ± 1·8 9·9 ± 0'6 42-8 ± 0'1 83 28 93·9 .± 1·5 153'2 ± 1'5 10·6 ± 1'2 39'4 ± 0·2 89 24 7-6 ± 0·2 10·2 ± 0'2 11 ·3 ± 0'4 41 ·3 ± 0'1 139 22

COllection Czechoslov. Chern. Commun. IVol. 341 (1969)

2776 Toma:

which is in good agreement with the value given by Jaifee32 (n = 0'683). We have further utilized these values (e, r) together with the rate constant values for the calculation of (J values for both heterocyclesandferrocenyl. Using the values determined for chalkones of the type A we obtained the results given in Table V, and -on employ­ing the values determined for chalkones of the type B the results given in the same table were attained. Fc = fcrrocenyl, (Ja. is the (J constant if the substituent is bound directly to the reaction center, i.e. if the entire substituted phenyl is substituted by ferrocenyl. We suppose that (JC6H S = O. '

Constants u for ferrocenyl were already determined by the measurement of dissociation con­stants of acids3 3- 35, phenols J3 and protonation of anilines3 3. The up value ( - 0'155) calculated by us is close to that determined by the measurement of the dissociation constants of acids ( - 0· 18

TABLE III

Reaction of Chalkones Containing Ferrocene Nucleus with Erhyl ex-Cyanobutyrate at 45°C --------_._ - - - -- .--_._ ... -

No X log e 104. k , min- 1 M.p., DC

nm (ref. 10)

Fc-CO-CH=CH-C6 H4 (X)

p-OCH3 338 4'31 9'8 ± 150 p-CH3 316 4·29 13·2 ± 1' 5 172-173

3 H 306 4·38 15'3 ± 1-3 139 4 p-F 308 4'34 16·3 ± 0'4 152

p-Cl 310 4'44 19'9 ± 160 m-Cl 299 4'32 25'1 ± 2 136-138 p-CN 303 4·41 41'2 ± 0·8 225 p-N02 318 4·40 56'3 ± 2·2 198

(X)C6 H4 CO-CH= CH- Fc

p-OCH3 328 4'40 11'1 ± 1·9 153-154 10 p-CH 3 325 4'27 18-4 ± 2 141-143 11 H 325 4·23 26·0 ± 135 12 p-F 330 4'24 25-4 ± 3'1 157-158 13 m-OCH3 325 4'27 28·6 ± 3·6 93- 94 14 p-Cl 330 4'29 38·7 ± 5'5 166- 168 15 p-Br 330 4'30 40·8 ± 163-165 16 m-Cl 330 4'22 147'1 ± 3·7 115- 116 17 m-Br 330 4'21 94-8 ± 6·3 116-118 18 p-CN 330 4'20 198·8 ± 10'7 168-169 19 m-N02 335 4·19 263·8 ± 34 149 20 p-N02 335 4'20 242,4 ± 20·6 221

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Michael Addition of Ethyl ex-Cyanobutyrate 2777

or -- 0'17), while the value obtained by other methods are considerably lower ( - 0'05 or - 0'03). 0"", constant which we determined is equal to that obtained by the measurement of the protonation of anilines. By measuring the dissociation constants of acids higher values were obtained ( - 0'15

FIG. 1

Dependence of log 103 • k on 0" for Chalko­

nes of the Type C6 H s-CO-CH= CH­- C6H 4 (X)

The numbering corresponds to that in Table I. Straight lines for 30° and 40°C are shifted to higher values by 0'7. Indication of temperatures: e 25°C, .. 35°C, • 45°<:=, () 30°C. 0 40°C.

TABLE IV

36 ,-

log 10J_k

30

, 24 I

0 0

18

12/?:

- 08

7

56 l jl 4

II

-0-4

Characteristics of the Correlations of log k and 0" for Chalkones of Type A and B

Temperature °C

25 30 35 40 45

25 30 35 40 45

1'103 1·092 1-041 1'032 1'054

1·687 1·695 1-693 1·624 1'597

Type A

0·992 0·991 0'989 0·990 0'986

Type B

0'997 0·991 0·998 0'998 0'997

Collection Czechoslov. Chem. Commuil. IVo\. 341 (1969)

S(!

0·059 0'065 0·035 0'044 0'070 0·088 0·017 0·022 0'068 0'085

0·039 0·053 0'075 0'101 0·037 0·049 0·033 0'044 0·040 0·054

8

I

110

0-4 08

2778

11

2-4 • ·12

loglO'k 10

8 . 9

2 0 . e

°

l6 1.7 6

3 4.5 . °5

12 0 2

-02 0·2 ()4 OS

" OS

FIG. 3

Dependence of log 104 . k on a for Chalkones

FcCOCH= CHC6H 4(X) 0 and FcCH= = CHCOC6 H4 (X) • at 45°C

The indication of points corresponds to that in Table III, Fc = ferrocenyl.

Toma:

FIG. 2

Dependence oflog }O3 . k on a for Chalkones of the Type (X)C6 H 4 -CO-CH= CH­-C6 H S

The numbering corresponds to that in Table II. The straight lines for 30°C and 40°C are shifted to higher values by 0'7. Indication of temperatures: e 25°C, 0 35°C, • 45°C, __ 30°C, f) 40°C.

1-1 2 18

1

06

FIG. 4

1·2 18

13 12

24 )0 log 10)k

25,

Dependence of log 103 . k4S on log }O3 . k 2S

for Chalkones C6 H 5CH= CHCOC6 H4 (X) • and (X)C6H 4 CH= CHCOC6 H s 0

The numbering of points corresponds to that in Table I and II. The straight line 0

is shifted to higher values by 0·3.

Collection Czechoslov. Chern. Commun. /Vol. 34/ (1969)

Michael Addition Of Ethyl ct-Cyanobutyrate 2779

or - 0'07). Constants ua; known from the literature are much lower (-0'23 to - 0'44) than those calculated by us ( - 0'582).

In order to ascertain that all chalk ones of the type A as well as those of the type B (includingferrocene, thiophene and furan analogues) can be considered as belonging to one reaction series, and hence, that Hammett's equation can be applied to them, we carried out the test described by Exner36. We plotted log "45 against log /(2 5

(Fig. 4). A linear relationship was obtained for chalkones of type A, b = 0'947, r = 0'999, Sb = 0'016, S = 0·026 (calculated for points 1-10). For chalkones of type B we obtained b = 0'958, r = 0'999, Sb = 0·010 and S = 0·026 (calculated for points 1-13). As the order of substituents is not changed, the application of Hammett's equation is substantiated. The only exception is substance No 15 of type A, where ferrocenyl is bound directly to the ~-carbon of the double bond, which is the site of the attack of the reagent. This point is rather deviated from the straight line, and therefore the given derivative cannot be inserted into the reaction series and we

TABLE V

Calculated Constants for Chalkones of the Type A and B

Temperature 2-Thienyl (u(%) 2-Furyl (ua) Fc(ua) Fc(up) Fc(urn) DC -~~~~-~---.--

Type A

25 - 0,086 - 0'205 ( - 0'602) - 0'144 - 0'004 30 - 0'132 - 0-241 (-0'563) - 0'176 - 0-009 35 - 0-143 - 0·226 ( - 0-509) - 0-145 - 0-000 40 -0-168 - 0,221 ( - 0'479) -0,159 -0,040 45 - 0-201 -0,233 (- 0'420) - 0'187 - 0'020

Average -0-146 - 0'225 (-0'515) - 0-162 - 0-014 ± 0'042 ± 0-013 ± 0'073 ± 0'015 ± 0-016

Type B

25 - 0,050 + 0' \04 - 0'582 - 0-140 + 0'030 30 - 0'050 + 0'130 - 0-561 - 0'134 + 0-014 35 - 0'053 + 0' 101 - 0·553 - 0'133 +0'013 40 -0'065 + 0-074 - 0'595 - 0'147 + 0'008 45 - 0'070 + 0' 111 - 0'620 - 0'179 - 0'012

Arerage - 0,058 + 0' 104 - 0'582 - 0'147 + 0'010 ± 0'009 ± 0'020 ± 0'026 ± 0'019 ± 0'015

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2780 Torna:

cannot calculate a constants for it. (a constants in Table V are in brackets.) The anomalous position of this derivative is further corroborated by the relatively large value of E and by the very small value (in comparison with other substances) of - l'lS* (Table 1). We explain this by the fact that ferrocenyl bound to the carbon atom which is the site of the attack of the reagent represents a steric hindrance to the course of Michael addition.

The magnitude of the value b (0·947 for type A and 0·958 for type B) is a proof that in the given temperature range the Michael addition 'is not temperature sensitive (Q == constant). The calculated E values and -l'lS* values which we calculated according t0 37 also point to this conclusion.

On comparison of the calculated a constants we found that ferrocenyl, if bound to the reaction center, be the latter the carbon atom of the carbonyl group or the ~-carbon atom of the double bond, has strong electron donor properties, stronger than 2-furyl or 2-thienyl. However, these latter two substituents behave in a different manner, depending on whether they are bound to the carbonyl group carbon atom or to the ~-carbon atom of the multiple bond. In the first case 2-thienyl has only very weak electron donor properties and 2-furyl has relatively strong electron acceptor properties. If both are attached to the ~-carbon of the multiple bond they have electron donating properties, 2-furyl behaving as a stronger electron donor. We explain this difference in behaviour by their I-effect which manifests itself strongly if they are bound to the carbonyl carbon atom. In the entire chalkone molecule the carbonyl group is primarily responsible for the polarity of bonds as well as of the whole mole­cule. Electron accepting properties of this group are saturated by the polarisation of the very mobile n-electrons of the double bond, which is also supported in the case of Michael addition by the attack of the reagent. Thus, if heterocycles are bound to the carbonyl group, this does not exhaust the electrons from them. This is also supported by the fact that the carbonyl group functions as a partial insulator of the conjugation38

• If heterocycles are bound to the ~-carbon atom, they are practically at the end of the conjugated system and also on the carbon carrying a positive charge, and therefore their M effect becomes manifest. The 2-furyl group behaves similarly to the methoxy group. If this is in para-position + M effect predominates, if in meta­position - I effect plays a greater role. Ferrocene, when bound to a benzene nucleus, has approximately the same electron donating effect as the methyl group.

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Collection Czechoslov. Chern. Cornmun. IVol. 34{ (1969)

Michael Addition ~f Ethyl o:-Cyanobutyrate 2781

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Translated by 1. Prochazka.

Collection Czechoslov. Chern. Cornmun. IVol. 341 (1969)