Nat. Chem.: Professor Tobias Ritter of Max Planck Institute of coal research in Germany reported the decarboxylation of carboxylic acids by CO and photocatalysis

As one of the most basic structural units in organic chemistry, olefins are widely used in the synthesis of polymers, detergents, lubricants, perfumes and pharmaceutical intermediates At present, the main source of olefins is non renewable resources such as oil It is an attractive way to prepare olefins from renewable raw materials carboxylic acid Decarboxylation of carboxylic acids can be traced back to 1960, but up to now, the reported synthesis methods need to use at least one stoichiometric additive, which limits its large-scale application Olefins can be obtained by decarboxylation of carboxylic acids catalyzed by transition metals, but both homogeneous and heterogeneous catalysts can only work in the presence of stoichiometric additives (such as anhydrides and phosphides), and the reaction needs high temperature (110-250 ℃), which usually leads to the isomerization of double bonds Redox active esters can also be converted to olefins under redox and photocatalytic conditions, but this method requires functionalization of carboxylic acids in advance to obtain the active ester substrate In addition, the oxidative decarboxylation of enzyme can only be carried out under the condition of stoichiometric additives (such as H 2O 2, NADH, etc.) Recently, Professor Tobias Ritter of Max Planck Coal Research Institute in Germany successfully converted fatty acids into α - olefins by CO catalysis of cobalt and light This method does not need to use stoichiometric additives, has a wide range of substrate applications, and the carboxylic acid with complex structure can also be well compatible In addition, the method can be applied to the later modification of natural and non natural products and the discovery of new drugs The related research results are published on nature Chemistry (DOI: 10.1038 / s41557-018-0142-4) (source: nature Chemistry) the author's research inspiration comes from abundant photocatalytic and proton reduction catalytic reactions The conversion of carboxylic acid to olefin by decarboxylation undergoes a double electron oxidation process of carbon chain Therefore, in the absence of stoichiometric oxidant, the conversion must release two hydrogen, while the protonation of [CO III] - h can release hydrogen Therefore, the co catalysis is realized by the single electron transfer between the photocatalyst and cobalt catalyst The decarboxylation of carboxylic acid and the generation of alkyl radicals are completed by the photocatalysis cycle of iridium, and then the olefin is converted and hydrogen is released under the catalysis of cobalt (Fig 1b) Firstly, the reaction conditions were screened and optimized with linoleic acid (3) as the model substrate, and finally CO (dmgh) 2 (4-ome-py) Cl (1) and IR [DF (CF 3) PPy] 2 (dtbpy) pf 6 (2) were determined as the best catalysts (Fig 1a) Under blue LED irradiation, with DME / H 2O (18:1) as solvent, 5 mol% 1 and 1 mol% 2 as catalyst, 20 mol% CS 2CO 3 as additive, the target product 3B can be obtained in 76% yield (source: nature Chemistry) furthermore, the range of substrates for the reaction was extended As shown in Table 1, due to mild reaction conditions, a variety of carboxylic acids with complex structures can be well compatible Linolenic acid (6) and eicosapentaenoic acid (7) are well tolerated to oxidative sensitive polyunsaturated fatty acids, and there is no double bond isomerization in the reaction Primary, secondary and tertiary carboxylic acids (8-10) are suitable for this reaction The reaction can tolerate alkynyl (12 and 13), triazole (14), phenol (15), carbonyl (17 and 18), pyridine (21 and 27) and hydroxy (22), showing excellent functional group tolerance The reactions of α - N and α - O-substituted carboxylic acids (16 and 19) produce enamide and vinyl ether, respectively The complex olefinamide derived from natural peptide (29) or drug (28) can also be obtained by this reaction In addition, some natural products and drug molecules also have good tolerance, such as jasmonate (20), cholic acid (31) The reaction is not limited to the use of a catalytic amount of base, the use of an equivalent base can achieve a higher yield in a shorter reaction time (source: nature Chemistry) finally, the mechanism of the reaction was studied CO 2 and H 2 were detected by gas chromatography The results of stern Volmer analysis show that the possibility of CO III oxidation quenching excited state IR III is greater than that of carboxylate reduction quenching in DME Although no complexes of alkylcobalt or cobalt hydrides were observed during the reaction, alkylcoboxime 32 can be independently prepared by this reaction (Fig 2a) In the absence of photocatalyst 2, alkylcobaltoxime 32 reacts under blue LED irradiation and forms 1-butene in 90% yield 32 can keep stable under the dark condition of 35 ℃, which shows that light is very important for the conversion of olefins When catalyst 1 is replaced by alkylcoboxime 32, carboxylic acid 8 is converted to olefin 8b in 87% yield under the same reaction conditions, indicating that 32 is the appropriate catalyst for decarboxylation The ring opening product diene 33b was obtained by decarboxylation of CIS acrylic acid 33, which was consistent with the catalytic cycle of cobalt in Fig 1b Conclusion: Professor Tobias Ritter of Max Planck Institute of coal research in Germany has developed a method for preparing α - olefins from fatty acids without the use of stoichiometric additives The reaction has a wide range of substrate applications and can be applied to the later modification of natural and non natural products and the discovery of new drugs.