INTERACTION OF DIAZOACETiC ESTERS WITH SiLYL-SUBSTIIUTED ACETYLENES AND THE PRODUCTION OF I-H- AND 1,2-DI-HCYCLOPROPENE-3-CARBOXYLIC ACIDS AND THEIR ESTERS* UDC 542.91:547.512:547.467,2:547.1'128

I. E. Dolgii, G. Po Okonnishnikova, and O. M. Nefedov

The synthesis of esters of l-H-cyclopropene-3-carboxylic acids by the photodissociation of alkyl diazoacetates (ADA) in the presence of monosubstituted acetylenes is accompanied by the formation of a significant amount of insertion products of alkoxycarbonylcarbenes into the alkyl C--H bond, which complicates the separation and purification of the cyclopropenyl esters [2]. Moreover, the 1,2-di-H-cyclopropene-3-carboxylic acid derivatives are generally not obtained by this method. We have developed a preparative method for the synthesis of I-H- and 1,2-di-H-cyciopropene-3-carboxylic acids and their esters starting from trialkylsilyl-substituted acetylenes and ADA. Inasmuch as the C--H bond on the ring multiple bond in cyclopropenes has a nature resembling that of the acetylenic C--H bond [3], a facile hydrolytic cleavage of the silyl groups is to be expected for i- and 1,2-silyl-substituted cyclopropenes, as has been found for silylacetylenes [4], with the formation of l-H- and 1,2-di-H-cyclopropene, respectively. In connection with this we studied the interaction of ADA with the acetylenes (I). The dissociation of ADA was conducted in an eightfold molar excess of (I) at 100-110~ with Cu or CuSO4 as catalyst. Thus, we obtained the corresponding esters of the l-alkyl-2-(trialkylsilyl)- or 1,2-bis(trialkylsilyl)cyclopropene-3-carboxylic acids (II) in yields of up to 54% (Table I). H~COOR a/Cu Or CuSO~ /\ RzC----CSiRa1-{- N~CHCOOR -N, * / / . , _\\ ~R2

SiRs1

(I)

(U)

R = R' = Me, R s = Me (W, n-Pr (b),n-Bu (c),t-Bu(d),.-CsHn~(e),n-GslI1,(f), SiM% tg); R = M e , RX----n-Bu, R S = n - P r (h); R = E t ,

RX=Me, RZ=t-Bu (i),

SiMe3 (j) 9 For previous article see [I]. TABLE I . Esters of 1,2-Disubstituted Cyclopropene-3-carboxylic Acids H\/COOH

//\\ / R2

\ SiR89 IR

{v,cm-I

Com R'

pound

R

(Ila (Iib (IIc (IId (IIe (II| (I~ (II (II: (II

Me Me Me .Me Me Me Me Me Me Me Me Me Me Me EMte n-Bu Et

d42o C=O

Me Me

Me

n-Pr n-Pr t-Bu n-CbH~l

37,5 15 41

n-Call17

SiMes

n-Pr t-Bu SiMe~

L5

Tl'ace$

67-69(10) i05(i8) i07,5 - i08,5

76,5-77(8)

(13)

t18(15)

151-t51,5 (7)

85-87(i0) 150-153(2)

t,4460 t,4487 t,4502 t,4435 1,4490 i.4538 L4485 1,4645

0,9280 0,9it0 0,9078 0,8892 0,90'74 0.890t 0,88il 0,89i2

1725

1730 i725 i730 i725 t725 i730 i720 1730 i730

C~C

183@ 1830 i830

1820 i820 1830 i900 1820 !820 1900

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 822-829, April, 1979. Original article submitted December 7, 1977.

0568-5230/79/2804-0765507.50

1979 Plenum Publishing Corporation

765

Me

SiMe,

SiMes

(IVb)

(lye) Et

Et

VBu

(lVa)

Et

8iMes

(III)

]

R

Pyrazoles

pot~nd

TABLE 2.

Rs

II N \

/ NR ~

CH~COOCzH~

CHzCOOCH3 70,8-70,9

i22-i23

73,5-75

t38,5

mL ~

SiMea II --COaR t

CH2COOC~Hs

H

R

t580

t720, 1760

1720, i750

i720

C==O

3150br

NH

IR(v, c m ' l ) ~ I

12,44S

HN

5,25

5,i5s

5,2s

m

NCR2

R2

1,4t (CH3)

4,3q (CHz)

4,34 q (CH2) 1,39t (CH~) 3,77s (CH~)

C02R'

Rt

4,iq (CH2) 1,2t (CH~)

4,3q (CH2) t,05t (CH3) 4,23q (CI-I2) 1,29t (CH~) 3,69S (CH:0

PMP~ (~, ppm)

t,40s .

R

0,33s 0,30s 0,32s 0,29s

0,39s

0,267s

SiMea

l-Alkylcyclopropene-3-carboxylic Acids (Vl)

TABLE 3.

C H\/COOH A

/

/\ d_ \

R Corfl pouno~

R

(VI6) | n-Pr (VIr)| t-Bu

\

H8

1IR (v,cM-~)

Pi'r (~,pprn)

I c=o

HA

d,2~

nap.,~

|

(vi~)/,~-c~rI,,|

(Vie) | n-CsHi7 |

,~

" 1,4605 t,~04 41,5 ,l

oil

)>

~ i,~io

t690 i700

c=c

18t0

1790

o,~83 ~69o ~8~5

! 1,4676 0,9596 i690

1805

10,52 ti,2 s iO,9i s t0,34 s 10,25 ~

li B 6,23 m 6,im 6,08 m 6,02 m 6,02 in

I~C 2,00d 2,00d 2,06d 2,00 d 2,00 d

The structure of the ester (II) was confirmed by the IR and PMR spectra) by elementary analysis, and by the adduct obtained with 1,3-cyclopentadiene (CPD) [5]. As in the case of the vinyl- and alkynylsiianes [6, 7], in the IR spectra of (II) the valence vibration band of the ring C = C bond (1800-1820 cm -I) is shifted by 50-100 cm -I to the long-wave region in comparison with the carbon analogs (1875-1913 cm -I) [8], which is explained [6] as the influence of the heavy atom and also by the presence of p~--d~ conjugation in unsaturated organosilicon systems. The use of methyl diazoacetate (MDA) instead of ethyl diazoacetate (EDA) in this reaction leads to increased yields of the esters (II) (see Table I). The influence of the substituents on the activity of the multiple bond of the starting material (I) under conditions of thermocatalytic interaction with ADA agrees with the expected steric and electronic effects. Thus, upon transition from n-propyl(trimethylsilyl)acetylene (Ib) to n-propyl(tributylsilyl)acetylene (Ih) with strong shielding of the multiple bond, the yield of the corresponding adduct with methoxycarbonylcarbene decreases from 40 to 1.5%. The corresponding cyclopropenes (IIg, d) are similarly formed in yields of only 8 and 15% from MDA and bis(trimethylsilyl)- (Ig) and tert-butyl(trimethylsilyl)acetylene (Id), whose triple bonds are shielded by bulky substituents. The low yields of the cyclopropenes (II) in the case of (Id) and especially of (Ig) might also be related to the significant decrease in the nucleophilicity of the acetylenic bond due to the p~--d~ conjugation with the participation of one or two Si atoms [6, 9, I0]. This combination of the steric and electronic effects of the substituents on the acetylenes (Id, g) means that the major reaction products are the pyrazoles (III) and (IV), which are formed in total yields of ~60% (Table 2). A/Cu or CuS~ RC-----CSiMe,+ N~CHCOOAIk (Id, g) R SiMe3 R SiMos 1 R SiMes

-.)< (ml

+ N~--COOAlk NCH~COOAIk (IV)

The structures of (III) and (IV) are supported by elementary analysis and also by the IR and PMR spectra. The formation of the pyrazoles proceeds through pyrazolenines, products of the 1,3dipolar addition of ADA to the alkyne. The isomerization of the pyrazolenines containing a hydrogen in position 3 to the thermodynamically stable pyrazoles proceeds spontaneously by a 1,5-sigmatropic shift of the migratory hydrogen to the nitrogen [II]. The 3-(trimethylsilyl)-4-tert-butyl- or 3,4-bis(trimethylsilyl)-5-alkoxycarbonylpyrazole (III) formed in this way contains an active N--H bond which further reacts with ADA to form the l-alkoxycarbonylmethyl-3-(trimethylsilyl)-4-tert-butyl- or l-alkoxycarbonylmethyl-3,4-bis(trimethylsilyl)-5-alkoxycarbonylpyrazole (IV).

767

--A

OO

*Reagent:

-5 ~

-5 ~

5% methanolic

2hat

2 h at

t-Bu n-CsH,7

(VII d)

(vii5

4,5 h at - 5 ~

-57

n-Bu 6i-62(ii) 97-98(3)

56,5-57 (3)

64@o) 52(8)

(p, tort)

bp, 0(2

i,4357 1,4520

1,4492

1,4432

nD

20

t730 1730

t730

t730 t730 1730

C=O

f795 1800

1805

1810 1810 i805

C=C

IR (v. c m -1)

amount of KOH.

0,9300 O,9075

0,9692

1,0t70

d~O

solution of an equimolar

64 52

64

48

2 h at

(vile)

54

"g.~.

0,5 h at - t 2 ~ 2,5 h at _5 ~

i(II)*

Me n-Pr

H

R

Reactionconl ditions,from

//\\

6,iid 6,25m

B,33m

6,83 d 6,33m 6,4m

HB

3,5ts 3,55s

3,588-

3,55s 3,658 3,668

CH30

R

Acids

2,06d 2,00d. 2,03d 2,00d 0,5- i,7m (CHs-CH~), 2,28 m (CH2C=C) 2,0Od 0,5-1,73m (CH~-CH~CH2), 2,48 m (CHiC=C) l,tOs 2,03d 0,5-i,75m (CHsCHzCH2), 2,02d 2,47m (CH2C=C)

H C

PMR (a. ppm)

Methyl Esters of Cyclopropene-3-carboxylic and l-Alkylcyclopropene-3-carboxylic CH\/COOMe

(vlIg) ( v i i a) (VlIb)

~ou~d

COlTI"

TABLE 4.

Regarding the mechanism of formation of cyclopropene esters under conditions of the thermocatalytic interaction of ADA with alkynes, one of the possibilities, according to Vidal et al. [2], is the elimination of N2 by the initially generated pyrazolenine (V) R

a/CusO.

~

RI

R

( H

\

OOAlk

R*

/

H/~COOAlk

(v) However, c o n s i d e r i n g t h e n o t i c e a b l y h i g h e r t e n d e n c y of a p y r a z o l e n i n e of t y p e (V) to i s o merize to a pyrazole under the conditions of this interaction, it is difficult to represent that this route might contribute a substantial portion to the formation of the cyclopropenes. More probably, the formation of cyclopropenes is represented as a result of the interaction of the original alkyne with a complex of the alkoxycarbonylcarbene a n d the catalyst. A decrease in the yields of the cyclopropene esters (II) due to the lowered nucleophilicity of the acetylenic bond (see Table i) also agrees with the carbene reaction mechanism. The treatment of the esters (II, R = A I k ) by aqueous or aqueous--alcoholic alkaline solutions at >-20~ leads to the l-alkylcyclopropene-3-carboxylic acids (VI) (Table 3) in yields of ~i00%. Upon lowering the reaction temperature to --50 to 0~ the predominant reaction is cleavage of the SiMe3 group, forming the corresponding esters (VII) Table 4) in yields of 50-65%.

CH~C00M e /

/\

H~/C00Me ./\ oH-

o~-

\

~-~-d

/

\

/ R

-->

/\

/

\

R

(VII)

CH ~/ C00H A \

\ SiMea

R

(Ira=0

HB

(Vi)

The production of (VII) under conditions of the low-temperature hydrolysis of (II) appeared possible due to the sharp decrease in the saponification rate of the ester group upon lowering the reaction temperature, while the rate of cleavage of the Si--C bond remained practically unchanged. Thus, from the methyl ester of 1,2-bis(trimethylsilyl)cyclopropene-3-carboxylic acid (IIg) at --12~ the methyl ester of cyclopropene-3-carboxylic acid (VIIg) was obtained

H~/C00Me

/\ / Me3Si/

CH~/C00Me

OH\

\ . SiMea (llg)

//\\

-i..~

BH/

\HB (Vllg)

The structures of the acids (VI) and their esters (Vll) are confirmed by the IR and PMR spectra, which agree with Arnaud's work [12], and also by the adduct of (VII) with CPD

[5]. The facile hydrolytic cleavage of the Si--C bond experimentally confirms the pseudoacetylenic character of the ring double bond in cyclopropene. Thus, the easier cleavage of the SiAlk3 group in the ester (IIg) in comparison with that in the esters (IIa-f) is probably related to the possible stabilization of charge in the carbanion COOAIk due to the vacant

/-

@

M%Si

3d o r b i t a ! s

o f t h e Si o f t h e second SiNe3 group.

Upon t r a n s i t i o n from t h e S~Me3 group t o Si(n--Bu) 3 a s i g n i f i c a n t d e c r e a s e i n t h e r a t e .of c l e a v a g e o f t h e Si--C bond o c c u r s , which i s e v i d e n t l y e x p l a i n e d by s t e r i c f a c t o r s , i n agreement with Bassindale e t a l . [13]. Thus, i f t h e rem oval of t h e s i l y l p r o t e c t i n g group i n t h e c a s e o f t h e m e t h y l e s t e r of l - n - p r o p y l - 2 - ( t r i m e t h y l s i l y l ) c y c l o p r o p e n e - 3 - c a r b o x y l i c a c i d ( I I b ) p r o c e e d s i n 0.5 h a t --5~ when t r e a t e d w i t h a 5% s o l u t i o n of KOH i n m e t h a n o l , t h e n t h e c l e a v a g e of t h e t r i - n - b u t y l s i l y l group from t h e m e t h y l e s t e r o f 1 - n - p r o p y l - 2 - ( t r i m e t h y l s i l y l ) c y c l o p r o p e n e - 3 - c a r b o x y l i c a c i d ( I I h ) when t r e a t e d w i t h t h e same r e a g e n t a t 0~

769

does not proceed at all, and at 20~ terminates only after 4 days. Here the rate of cleavage of the Si--C bond in (IIh) is practically the same as the rate of saponification of the ester group, as a result of which l-n-propylcyclopropene-3-carboxylic acid (VIb) and its ester (VIIb) are formed in approximately equal amounts. A further increase in temperature promotes saponification to a large degree, which leads to a predominance of the acid in the reaction products. EXPERIMENTAL Gas--liquid chromatographic analysis was conducted on an LKhM-8MD apparatus (300 • 0.2 cm column of 15% Reoplex 400 or 5% SE-30 on Chromaton N-AW-DMCS support, thermal conductivity detector, He carrier gas at 30 ml/min), and thi~-layer chromatography was on A1203 (activity II) with a benzene:ether (3:2) eluent. PMR spectra were obtained on a Varian DA-60IL with a PC-60M or a Bruker WP-60 (60 MHz) for 10-30% solutions in CC14, CHCI~, CDCI3, (CD3)2CO, and (CD3)2S0, with TMS as an internal standard. Chemical shifts are presented using the 6 scale. IR spectra were recorded on a UR-20 spectrophotometer (in films on KBr or in pellets). Properties of the synthesized Tables 1"4.

(II), (III),

(IV),

(VI), and (VII) are presented in

Methyl Esters of l,2-Disubstituted Cyclopropene-3-carboxvlic Acids (II). To a refluxing mixture of 78 g (0.7 mole) of methyl(trimethylsilyl)acetylene (la) and 0.016 g (0.0001 mole) CuSO4 was added over 12 h a solution of i0 g (0.i mole) methyl diazoacetate in ii g (0.i mole) (Ia). The mixture was heated until evolution of N2 ceased, and excess (Ia) was distilled off. From the residue, 9.9 g (54%) of the methyl ester of l-methyl-2-(trimethylsilyl)cyclopropene-3-carboxylic acid (IIa) was isolated. The esters (IIb-i) were synthesized analogously. In the case of bis(trimethylsilyl)acetylene, after isolation of the ester (IIg) (8%), a solid residue was obtained from which l-methoxycarbonylmethyl-3,4-bis(trimethylsilyl)-5methoxycarbonylpyrazole (IVb) (60%) was obtained by recrystallization from 96% ethanol. Obtained analogously was l-ethoxycarbonylmethyl-3-(trimethylsilyl)-4-tert-butyl-5-ethoxycarbonylpyrazole (IVa) (25%). With ethyl diazoacetate under analogous conditions bis(trimethylsilyl)acetylene forms a mixture of l-ethoxycarbonylmethyl-3,4-bis(trimethylsilyl)-5-ethoxycarbonylpyrazole (IVc) and 3,4-bis(trimethylsilyl)-5-ethoxycarbonylpyrazole (III), which is separated by fractional crystallization from the system heptane:methanol (1:5). l-Alkylcyclopropene-3-carboxylic Acid (V!),. A mixture of 1.8 g (0.01 mole) (IIa) and a solution of 1.2 g (0.021 mole) KOH in 6 ml of 80% ethanol were stirred for 20 h at 20~ By the usual method, 0.95 g (97%) l-methylcyclopropene-3-carboxylic acid (Via) was isolated. Similarly,

(VIb, e, g, h) were obtained.

Methyl Esters of l-Alkylcyclopropene-3-carboxylic Acids (VII). To a solution of 1.2 g (0.021 mole) KOH in 24 ml methanol, cooled to --40~ was added 4 g (0.021 mole) (IIa). The mixture was stirred 2.5 h at --5~ , and the end of the reaction was detected by TLC. Then the material was again cooled to --40~ and neutralized with a 5% solution of H2S04. After the mixture had warmed to 20~ it was diluted with five volumes of water and extracted with ether. The extract was washed with water, dried with MgSO4, and concentrated. From the residue 1.2 g of the methyl ester of l-methylcyclopropene-3-carboxylic acid (VIIa) (see Table 4) was isolated. Analogously obtained were (VIId, e, h, i). Methyl Ester of Cyclopropene-3-carbox~lie Acid (VII$). A mixture of 0.4 g (0.0017 mole) 1,2-bis(trimethylsilyl)cyclopropene-3-carboxylic acid methyl ester (IIg) and a solution of 0.14 g (0.0025 mole) KOH in 2.65 ml methanol were stirred 0.5 h at --12~ Then the reaction mass was cooled to --40~ neutralized with dilute H2SO~, and allowed to warm to 0~ After this the mixture was extracted with CC14, and the extract was dried by shaking for 15 min with MgSO4 and filtered. PMR and IR spectra were taken of the solution of (VIIg) obtained in this manner.

770

CONCLUSIONS I. The interaction of alkyl diazoacetates with trialkylsilylacetylenes was studied, and it was shown that increasing the bulkiness of the substituents and lowering the nucleophilicity of the multiple bond in these acetylenes leads to a decrease in the yield of esters of trialkylsilyl-substituted cyclopropene-3-carboxylic acids. 2. Under conditions of alkaline hydrolysis, trialkylsilyl groups are easily cleaved from esters of l-trialkylsilyl- and 1,2-bis(trialkylsilyl)cyclopropene-3-carboxylic acids, forming I-H- and 1,2-di-H-cyclopropenes, respectively. Thus, depending on the temperature of hydrolysis, either the cleavage of trialkylsilyl groups proceeds exclusively or simultaneously with the saponification of the ester group. LITERATURE CITED i.

2. 3. 4. 5. 6. 7. 8.

9. i0. ii. 12.

13.

i. E. Dolgii, G. P. Okonnishnikova, and O. M. Nefedov, Izv. Akad. Nauk, Ser. Khim., 1970, 197; O. M. Nefedov, I. E. Dolgii, G. P. Okonnishnikova, and I. B. Schwedova, Ang. Chem., 84, 946 (1972); I. E. Dolgii, G. P. Okonnishnikova, and I. B. Shvedova, Novel Carbenes [in Russian], Inst. Org. Khim. Akad. Nauk SSSR, Moscow (1973), p. 217; I. E. Dolgii, G. P. Okonnishnikova, ~. A. Baidzhigitova, and O. M. Nefedov, Fifth AllUnion Conference on the Chemistry of Acetylene [in Russian], Tbilisi (1975), p. 183; I. E. Dolgii, G. P. Okonnishnikova, and O. M. Nefedov, Inventor's Certificate No. 566,830, March 21, 1975; Byull. Izobr. No. 28 (1977). M. Vidal, F. Massot, and P. Arnaud, C. R. Acad. Sci., 268C, 423 (1969); M. Vidal, M. Vincens, and A. P. Arnaud, Bull. Soc. Chim. Fr., 1972, 657. G. L. Closs, Proc. Chem. Soc., 1962, 152. V. Bazant, V. Chvalovsky, and J. Rathousky, Organosilicon Compounds, Prague (1965), p. 214. I. E. Dolgii, G. P. Okonnishnikova, E. A. Baidzhigitova, A. Ya. Shteinshneider, and O. M. Nefedov, Izv. Akad. Nauk SSSR, Ser. Khim., 1977, 2592. V. Bazant, V. Chvalovsky, and J. Rathousky, Organosilicon Compounds, Prague (1973), p. i00. Ibid., p. 94. M. I. Komendantov, I. A. D'yakonov, I. Gokhmanova, and R. R. Kostikov, Zh. Org. Khim., !, 209 (1965); M. I. Komendantov and R. R. Kostikov, ibid., 4, 1128 (1968); M. Vidal, E. Cho!let , and P. Arnaud, Tetrahedron Lett., 1967, 1073. V. Bazant, V. Chvalovsky, and J. Rathousky, Organosilicon Compounds, Prague (1965), p. 17. I. A. D'yakonov and G. V. Golodnikov, Zh. Obshch. Khim., 35, 2181 (1965). R. R. Bekmukhametov, Current Problems of Organic Chemistry [in Russian], Vol. 5, Izd. Leningrad Univ. (1976), p. 105. P. Arnaud, J. L. Pierre, and M. Vidal, Bull. Soc. Chim. Fr., 1967, 3810; M. Vidal, J. L. Pierre, and P. Arnaud, ibid., 1969, 2864; M. Vidal, P. Arnaud, and M. Vincens, ibid., 1972, 665; K, Kimura, Sh. Hori, J. ilinato, and V. Odaira, Chem. Lett., 1973, 1209. A. R. Bassindale, C. Eaborn, R. Taylor, A. R. Thompson, and D. R. M. Walton, J. Chem. Soc. B, 1971, 1155.

771