New Efficient Catalysts in the Synthesis of Warfarin and Acenocoumarol
2
Warfarin and Acenocoumarol New Efficient Catalysts in the Synthesis of Warfarin and Acenocoumarol Neue wirksame Katalysatoren fur die Synthese von Warfarin und Acenocumarol Ivo C. Ivanov, Ilia Manolov*,and Liliana A. Alexandrova Institute of Pharmacologyand Pharmacy, Bulgarian Medical Academy, Dunav 2, BG-1000 Sofia, Bulgaria Received January 2 1.1990 In the preparation of the anticoagulants warfarin (3a) and its 4’-sub- stituted derivatives (e.g. acenocoumarol, 3b) by Michael addition of 4-hy- droxycoumarin (1) to the corresponding 4-aryl-3-buten-2-ones (2). ammon- ialV2), aliphatic or acromatic a m i n e ~ ~ . ~ ) , ~yridine~.~.~’, quinoline3”), alkali phosphate^^'^^'. sodium acetate or citrate3’, borax3’ and alkali alkoxides6) have been used as catalysts till now. We found out that by accomplishing this reaction in aqueous medium either alkali fluorides (KF, NaF) or quar- ternary ammonium salts (phase-transfer catalysts) can be applied as highly efficient catalysts (Table 1). For compari- son of the reaction times the addition process was carried out also without any catalyst (entries 1 and 12) and in the presence or triethylamine or trisodium phosphate (entries 10 and 11) being the most recommended catalysts in the lit- erature. Accomplished in pyridiae or in glacial acetic acid in the presence of sodium acetate the reaction gave dark-col- oured by-products and the purification of the products was complicated. Diluted sulfuric acid inhibited or stopped this reaction. The following general conclusions can be drawn from the experimental data presented in Table 1. First, for the preparation of warfarin (3a) the phase-trans- fer catalysts in optimum concentration of 5 mol per cent are more suitable. The yield of 3a is not essentially influenced by the nature of the quartemary salt. The use of these cata- lysts reduces the reaction time to about 5 % while the use of KF reduces it only to about 50 ‘% (entry 9). Even more, the catalysed processes give markedly higher yields of 3a. Second, the alkali fluorides in a concentration of 5 mol per cent are more useful for the preparation of acenocoumarol (3b). There is practically no difference in the effects of the salts used in entries 13 and 16. Alkali fluorides reduce the reation time to 33 9% while triethylbenzylammonium chloride (entry 17) shortens it to about 50 %. The simulta- neous application of both catalysts (entry 18) does not PH 52 1 enhance the catalytic effect, and the product isolated in these trials is of low quality. High yields are achieved when using the catalysts de- scribed above - nearly 80 % for triethylbenzylamrnoniurn chloride in 3a (entry 3) and for NaF in 3b (entry 16). The reaction mixture remains pale-coloured till the end of the process and the corresponding product can be isolated eas- ily in a rather pure state. The Michael addition occurs by refluxing in a heteroge- neous mixture, since 4-hydroxycoumarin (1) is soluble in hot water and the unsaturated ketone 2 is a melt. Obviously, fluoride ions act as a week basic catalyst with good solu- bility in the org. phase lo). However, complementary studies should be undertaken for a reasonable explanation of the catalytic effect of quartemary ammonium salts in the ab- sence of any base (in contrast to the numerous examples in lit. ”)). Experimental Part M.p.: Btichi 510 apparatus (Switzerland), uncorrected. - TLC: Al-foils Kieselgel 60 FZ4. Merck (FRG), developed by cyclohexane-chlorofom- acetic acid (10104, vol. parts), detection: UV 254 nm. - The reaction time is determined by TLC monitoring (till exhaustion of the starting 1). General procedure Water (160 ml) and the corresponding catalyst (Table 1) are added under stirring to a mixture of equimolar amounts (50 mmol each) of Chydroxy- coumarin (1) and unsaturated ketone 2a or b. Then the mixture is refluxed under vigorous stirring for a period shown in Table 1. The product is filtered, triturated and washed successively with hot water (3 x 100 ml) and, after cooling, with ether (2 x 50 ml). If necessary, the product can be recrystallized from glacial acetic acid or ethyl acetate. The yields are given in Table 1. 1 2 3 Arch. Pharm. (Weinheim) 323,521-522 (1990) OVCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1990 0365-~6233/90/0808-521 $3.50 + .25/0
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Transcript of New Efficient Catalysts in the Synthesis of Warfarin and Acenocoumarol
Warfarin and Acenocoumarol
New Efficient Catalysts in the Synthesis of Warfarin and Acenocoumarol Neue wirksame Katalysatoren fur die Synthese von Warfarin und Acenocumarol
Ivo C. Ivanov, Ilia Manolov*, and Liliana A. Alexandrova
Institute of Pharmacology and Pharmacy, Bulgarian Medical Academy, Dunav 2, BG-1000 Sofia, Bulgaria
Received January 2 1.1990
In the preparation of the anticoagulants warfarin (3a) and its 4’-sub- stituted derivatives (e.g. acenocoumarol, 3b) by Michael addition of 4-hy- droxycoumarin (1) to the corresponding 4-aryl-3-buten-2-ones (2). ammon- ialV2), aliphatic or acromatic amine~~.~) , ~yr id ine~.~ .~’ , quinoline3”), alkali phosphate^^'^^'. sodium acetate or citrate3’, borax3’ and alkali alkoxides6) have been used as catalysts till now.
We found out that by accomplishing this reaction in aqueous medium either alkali fluorides (KF, NaF) or quar- ternary ammonium salts (phase-transfer catalysts) can be applied as highly efficient catalysts (Table 1). For compari- son of the reaction times the addition process was carried out also without any catalyst (entries 1 and 12) and in the presence or triethylamine or trisodium phosphate (entries 10 and 11) being the most recommended catalysts in the lit- erature. Accomplished in pyridiae or in glacial acetic acid in the presence of sodium acetate the reaction gave dark-col- oured by-products and the purification of the products was complicated. Diluted sulfuric acid inhibited or stopped this reaction.
The following general conclusions can be drawn from the experimental data presented in Table 1.
First, for the preparation of warfarin (3a) the phase-trans- fer catalysts in optimum concentration of 5 mol per cent are more suitable. The yield of 3a is not essentially influenced by the nature of the quartemary salt. The use of these cata- lysts reduces the reaction time to about 5 % while the use of KF reduces it only to about 50 ‘% (entry 9). Even more, the catalysed processes give markedly higher yields of 3a.
Second, the alkali fluorides in a concentration of 5 mol per cent are more useful for the preparation of acenocoumarol (3b). There is practically no difference in the effects of the salts used in entries 13 and 16. Alkali fluorides reduce the reation time to 33 9% while triethylbenzylammonium chloride (entry 17) shortens it to about 50 %. The simulta- neous application of both catalysts (entry 18) does not
PH
52 1
enhance the catalytic effect, and the product isolated in these trials is of low quality.
High yields are achieved when using the catalysts de- scribed above - nearly 80 % for triethylbenzylamrnoniurn chloride in 3a (entry 3) and for NaF in 3b (entry 16). The reaction mixture remains pale-coloured till the end of the process and the corresponding product can be isolated eas- ily in a rather pure state.
The Michael addition occurs by refluxing in a heteroge- neous mixture, since 4-hydroxycoumarin (1) is soluble in hot water and the unsaturated ketone 2 is a melt. Obviously, fluoride ions act as a week basic catalyst with good solu- bility in the org. phase lo). However, complementary studies should be undertaken for a reasonable explanation of the catalytic effect of quartemary ammonium salts in the ab- sence of any base (in contrast to the numerous examples in lit. ”)).
Experimental Part
M.p.: Btichi 510 apparatus (Switzerland), uncorrected. - TLC: Al-foils Kieselgel 60 FZ4. Merck (FRG), developed by cyclohexane-chlorofom- acetic acid (10104, vol. parts), detection: UV 254 nm. - The reaction time is determined by TLC monitoring (till exhaustion of the starting 1).
General procedure
Water (160 ml) and the corresponding catalyst (Table 1) are added under stirring to a mixture of equimolar amounts (50 mmol each) of Chydroxy- coumarin (1) and unsaturated ketone 2a or b. Then the mixture is refluxed under vigorous stirring for a period shown in Table 1. The product is filtered, triturated and washed successively with hot water (3 x 100 ml) and, after cooling, with ether (2 x 50 ml). If necessary, the product can be recrystallized from glacial acetic acid or ethyl acetate. The yields are given in Table 1.
1 2 3
Arch. Pharm. (Weinheim) 323,521-522 (1990) OVCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1990 0365-~6233/90/0808-521 $3.50 + .25/0
522 Ivanov, Manolov. and Alexandrova
Table 1: Influence of some catalysts on the synthesis of 3a, b
Entry Product Catalyst (amount) No.
Dura- Yield.” M.p.,OCb) tion, h %
1 3a Without catalyst5) 42 46 160-161 2 Triethylbenzylammonium
3 Triethylbenzylammonium
4 Triethylbenzylammoniun
5 Tetrabuty lammonium
6 Benzyltributylammonium
7 Tetraoctylammonium
chloride (2.5 rnol %) 2 66 155-158
chloride (5 mol %) 2 83 155-158
chloride (10 rnol %) 2 84 155-158
chloride (5 mol %) 3 77 150-154
chloride (5 rnol %) 2 83 156- 159
bromide (5 mol %) 3 75 155-1 57 8 Aliquat 336 (5 mol %) 2 68 158-160 9 KF (5 mol %) 20 71 158- 162 10 Triethylamine’*3)
(7.7 mol %) 3 67 159-161 11 Na$O:8) (6 rnol %) 10 57 159-161 12 3b Without catalyst 6 78 C)
13 KF (5 mol %) 2 77 C)
14 KF (10 rnol %) 2 83 C)
15 NaF (15 mol %) 2 75 C)
16 NaF (5 rnol %) 2 79 C)
chloride (5 mol %) 3 88 C)
17 Triethylbenzylammonium
18 KF (5 rnol %) + triethyl- benzylammonium chloride (5 mol %) 2 92 157-1 80
coloured
Notes: a) Yield of isolated product without recrystallization, TLC homogeneous. - b, The m.p. corresponds to the product obtained with the given yield. - c, The tipical m.p. of the crude acenocoumml is in the rahge 192-196OC (lit.’*): m.p. 196-199OC).
References
1
2 3 4 5
6
D.F. Starr and K.K. Haber, US Pat. 2 666 064 (1954); C.A. 49,380h (1955). H.G. Krey, DDR Pat. 15092 (1958); C.A. 54.3458de (1960). C.G. Joshi and J.L. Bose, Indian J. Technol. 10,461 (1972). J.D. Rizzo and P.J. Davis, J. Pharm. Sci. 78, 183 (1989). M. Ikawa, M.A. Stahmann, and K.P. Link, J. Am. Chem. SOC. 66,902 (1944); US Pat. 2 427 578 (1947): C.A. 42, P603h (1948). W . Stoll and F. Litvan, US Pat. 2 648 682 (1953). Geigy AG, Basel; C.A. 49, P 2522fg (1955).
7 S. Lacobescu and T. Gostea, Fr. Pat. 1 271 976 (1962); C.A. 56.
8 P. Spiess and W. Spiess, Brit. Pat. 734 142 (1955); C.A. 50, 7143a (1956).
9 K. Knoevenagel, D.O.S. 948 507 (1956). C.F. Spiess & Sohn and Norddeutsche Affinerie; C.A. 53.2258 g (1959).
10 R. Curci, M. Fiorentino, L. Troisi, J.O. Edwards, and R.H. Pater, J. Org. Chem. 45,4758 (1980).
11 E.V. Dehmlow and S.S. Dehmlow, Phase Transfer Catalysis, 2nd Ed., Verlag Chemie, Weinheim, 1983.
12 The Merck Index, 10th Ed., p. 29, Rahway, USA, 1983.
15488g(1962). ‘
[KPh528]
Arch. Pharm. (Weinheim) 323,521-522 (1990)
