J. Org. Chem. 1983,48,3803-3807
3803
Regioselective Hydroesterification and Hydrocarboxylation of 3,3,3-Trifluoropropene and Pentafluorostyrene Catalyzed by P hosphine-Palladium Complex Takamasa Fuchikami, Katsuyuki Ohishi, and Iwao Ojima* Sagami Chemical Research Center, Nishi-Ohnuma 4-4-1, Sagamihara, Kanagawa 229, Japan
Received February 14, 1983 The hydroesterification and hydrocarboxylation of 3,3,3-trifluoropropene(TFP) and pentafluorostyrene (PFS) catalyzed by phosphine-palladium complexes were studied. It was found that the efficiency and the product distribution of the reaction depended markedly on the nature of nucleophile, Le., water or alcohol, the structures of olefin and phosphine ligand, and other reaction variables such as solvent, temperature, and carbon monoxide pressure. Under optimal conditions either unbranched products or branched products were obtained in high yields with high regioselectivities. For example, 4,4,4-trifluorobutyricacid (5a) was obtained in 93% yield with 99% regioselectivity by using PdCl,(dppf)-SnCl, as the catalyst in the hydrocarboxylation of TFP while ethyl 2-methyl-3,3,3-trifluoropropionate (2a) was obtained in 96% yield with 79% regioselectivity in the hydroesterifcation of TFP by using PdC1,(PPhJ2 as the catalyst. Similarly, 3-(pentafluoropheny1)propionic acid (5b) was obtained in 93% yield with 99% regioselectivity in the hydrocarboxylation of PFS catalyzed by PdCl,(dppf), and methyl 2-(pentafluorophenyl)propionate(2b) was obtained in 89% yield with 95 % regioselectivityin the hydroesterification of PFS catalyzed by PdCl,(PPh,),. Possible mechanisms of the present reactions are discussed. The hydrocarboxylations of TFP and PFS may involve (hydroxycarbonyl)palladium(II)intermediates while the hydroesterificationsof TFP and PFS may proceed via alkylpalladium(I1) and acylpalladium(I1) intermediates. It is known that the hydrocarbonylations of olefins serve as a convenient device for the production of the corresponding esters and carboxylic acids.' Although mechanistic studies as well as applications of the reactions to organic syntheses have been extensively studied, little is known about the reactions of olefins bearing perfluoroalkyl and perfluoroaryl substituents.2 Recently, it has been shown that unique physiological activities are often obtained by introducing a trifluoromethyl or pentafluorophenyl group into a biologically active c ~ m p o u n d . ~As 3,3,3-trifluoropropene (TFP) and pentafluorostyrene (PFS) are important fundamental building blocks, we have been studying the functionalizations of these compounds, e.g., arylation,* Diels-Alder reaction^,^ ureidocarbonylation,6 hydro~ilylation,~ and hydroformylation.8 In the hydroformylation of TFP and PFS, we found that the regioselectivity of the reaction was unusually high and dependent markedly upon the catalyst metal species employed; e.g., the rhodium complex catalyzed reaction of TFP gave branched aldehyde in more than 95% selectivity while the cobalt carbonyl catalyzed reaction gave unbranched aldehyde in 93% selectivity.8 The results make a sharp contrast to those of ordinary olefins such as propene, hexene, styrene, ethyl acrylate, etc.l These findings compelled us to examine other hydrocarbonylations of TFP
(1) (a) Wender, I.; Pino, P. "Organic Synthesis via Metal Carbonyls"; Wilev-Interscience: New York, 1977. (b) Falbe. J. "New Svntheses with Carbon Monoxide"; Springer-Verlag: .West Berlin, 1980. " (2) (a) Rudkovskii, D. M.; Imyanitov, N. S.; Gankin, V. Y. Tr., Vses. Nauchno-Issled. Inst. Neftekhim. Protsessov 1960, 121; Chem. Abstr. 1962,57,10989. (b) Roehrscheid,F. (Hoechst A. G.) Ger. Offen. 2 163 752, 1973; Chem. Abstr. 1973, 79, 78110m. (c) Roehrscheid, F.; Billenstein, S. (Hoechst A. G.) Ger. Offen. 2 137 712, 1973; Chem. Abstr. 1973, 78, 110601q. (3) For example: (a) Smith, F. A. CHEMTECH 1973,422. Filler, R. Ibid. 1974, 752. (b) Lin, T.-S.; Chai, C.; Prusoff, W. H. J. Med. Chem. 1976, 19, 915. (4) Fuchikami, T.;Yatabe, M.; Ojima, I. Synthesis 1981, 365. (5) Ojima, I.; Yatabe, M.; Fuchikami, T . J . Org.Chem. 1982,47, 2051. (6) Fuchikami, T.; Ojima, I. Tetrahedron Lett. 1982, 23, 4099. (7) Ojima, I.; Yatabe, M.; Fuchikami, T.43rd Annual Meeting of the Chemical Society of Japan, 1981, Abstract No. 1D06. (8) Fuchikami, T.; Ojima, I. J. Am. Chem. SOC.1982, 104, 3527.
and PFS. Now, we describe here the hydroesterification and hydrocarboxylation of TFP and PFS catalyzed by phosphine-palladium complexes, in which the former reaction gives branched esters whereas the latter gives unbranched carboxylic acids with high selectivities.
Results and Discussion Hydroesterification of TFP and PFS. First, we examined the catalytic activities of typical transition-metal complexes such as CO2(CO)8, Rhs(CO)16, H2PtC&/ SnC12-acetone, and PdC12(PPh3)2toward the hydroesterification of TFP and PFS with methanol and carbon monoxide a t 100 "C and 110 atm, and it was found that only PdC12(PPh3)2showed the catalytic activity enough to promote the reaction under the given reaction conditions. Thus, we decided to employ palladium complexes with phosphine ligands for the present study (see eq 1). R,CH=CHz
+
CO
+
ROH
[Pdl
l a , Rf = CF, b, Rf = C,F,
+
Next, we looked a t the effects of reaction variables on the conversion and regioselectivity of the reaction. Table I summarizes the effects of the ratio of triphenylphosphine to palladium and the solvent effects on the reaction of TFP. As Table I indicates, (i) a PPh3/Pd ratio of 2 gave the best yield (entry 2), (ii) existence of triphenylphosphine is a r e q ~ i s i t ebut , ~ large excess of it decreases the catalytic activity (entry 4),and (iii) the PPh3/Pd ratio exerts an (9) When the reaction was carried out with 10 mmol of TFP, 3 mL of ethanol, and 0.10 mmol of PdC12in 10 mL of acetone at 100 "C and 110 atm of carbon monoxide, the yield of the esters was only 3%.
0022-3263/83/1948-3803$01.50/0 0 1983 American Chemical Society
3804 J . Org. Chem., Vol. 48, No. 21, 1983
Fuchikami, Ohishi, and Ojima Table I. Hvdroesterification of T F P conditions
entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
catalyst PdC1, + PPh, PdCl, + 2PPh, PdCl, + 4PPh, PdCl, + lOPPh, PdCl,( PPh,), PdCl,(PPh,), PdC1,( PPh,), PdCl,(PPh,), PdC1,( PPh,), PdCl,(PPh ,), PdCI,(PPh,), PdC1,( PPh,), PdCl,(PPh,), + 5SnC1, PdC1,( dppb)d PdCl,(dppb)d PdC1,( dppf)e PdC1,( dppf)e PdC1,( PPh,), PdC1,( PPh,),
solvent
temp, 'C
time,
alcohol
!l
yield, %
EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH MeOH i-PrOH
acetone acetone acetone acetone EtOH acetone tetrahydrofuran toluene benzene acetonitrile triethylamine NaOAcC/EtOH benzene acetone benzene acetone benzene benzene benzene
100 100 100 100 100 100 100 100 100 100 100 100 100 120 120 120 120 100 100
70 70 70 70 62 62 62 62 62 62 40 40 30 53 66 83 66 62 62
29 62 59 23 74 82 93 96 95 96 0 0 6 12 13 16 50 95 93
branched (2a)/unbranched (3a) ratio 46/54 49/51 43/57 31/69 49/51 52/48 71/29 77/23 79/21 79/21
