Decarboxylation and Decarbonylation

2 Decarbonylation and Decarboxylation - The photochemical reactions between carboxylic acids such as formic and trifluoroacetic acid and silica surfaces have been studied. The irradiation of diphenylacetic acid in acetonitrile with acridine results in the decarboxylation and the formation of the adduct (102). When the two achiral compounds, acridine and diphenylacetic acid, are cocrystallized a chiral two component molecular crystal is obtained in which the components are present in a 1 1 ratio. Both (—)- and (+)- crystals can be obtained. This crystalline material is photochemically reactive and irradiation brings about decarboxylation and formation of the adduct (102) with an ee of 35%. This compound is accompanied by a low yield of (103) which is formed exclusively on irradiation of the reactants in acetonitrile solution.Photochemical decarboxylation can be brought about by the irradiation of benzilate (104)/ methyl viologen pairs.  

Barton ester system for the generation of specific radicals. In one example, the oxiranyl radicals (116) have been formed by the uranyl-glass-filtered irradiation of the substrate (117) and cyclize to yield (118) as the final product.  

A full report of the laser-induced enantio enrichment of tartaric acid, originally published in preliminary form, has appeared.  

The photochemical fragmentation of 7-methyl-2,2,5-triphenyl-l-oxa-5,6-diaza-spiro-[2,4]-hept-6-en-4-one has been studied. Interest in solid state photochemistry continues to burgeon. The present paper discusses the problems associated with the proximity of the components of radical pairs or biradicals within the constrictions of the crystalline environment. This problem has been addressed by examining the photochemical reactivity of a series of cyclohexanone derivatives (119) whose solution-phase photochemistry is well known. The irradiations, using X = 350 nm, were carried out on microcrystals dispersed in potassium bromide. The influence of the conformations within the crystals and substitution were studied. The relative yields of the product, the corresponding cyclopentane, are shown beside the appropriate structure.  

1 Decarbonylation and Decarboxylation - The kinetics of the decarbonylation of benzaldehyde into benzene and carbon monoxide has been reported in detail. The m-di-/-butylcyclopropanone (62, R = H) has been synthesised and photochemically this readily undergoes decarbonylation to yield the corresponding cis- 

Photochemical decarbonylation has also been used as a route to enols. Thus irradiation of the indanone (67) leads to the formation of the two enols (68) and (69). The lifetime of the enols and their reactivities were assessed. Maier and coworkers have demonstrated that irradiation at 254 nm of CO and CS in a low temperature matrix leads to the formation of the thioxoetheneone (70).  

Decarboxylation is also a common photochemical reaction. The results of a 

The degradation, by decarboxylation, of a-naphthaleneacetic acid has been shown to be wavelength dependent. Short wavelengths are the more destructive and the decarboxylation follows pseudo-first order kinetics. The photodegradation of 2,4-dihydroxybenzoic acid in water catalysed by titanium dioxide has been reported in some detail.  

A laser-flash examination of the photochemical behaviour of ketoprofen (73) in water has shown that deprotonation occurs with decarboxylation following as a second step to yield the benzylic anion (74). Interestingly this anion exhibits both anionic and radical characteristics. In another study of compound (73) 

Mehta and Ravikrishna have demonstrated that the monosubstituted semibullvalenes (155) can be readily prepared by photodecarbonylation of the polycyclic ketones (156). The reaction is best carried out in methanol solution. 

Irradiation of (157) through Pyrex brings about decarbonylation and the formation of the tetraene (158) which on further irradiation using X, 220 nm gives a low yield of the (4 + 4)-adduct (159). The photodecarbonylation of e i6 -tricyclo[5.2.2.0 ]undecadienones has been reported.  

An efficient route for the synthesis of [2.2]cyclophanes has also been described which involves the photochemical double decarbonylation of the diketones (160), (161) and (162). The reactions are carried out in argon-degassed benzene solution and give high yields of products efficiently. In the case of the meta systems (160) both mono (163) and double decarbonylation products (164) are formed, but with (161) and (162) only the bisdecarbonyla-tion is observed affording (165) and (166) respectively. 

Irradiation of the oxazolone derivative (167) in acetonitrile results in decarbonylation and the formation of the imine (168) In the presence of allyl alcohols, trapping (a thermal reaction) of (168) results in the formation of the ethers (169) which undergo Norrish Type II hydrogen transfer and the formation of the isomeric compounds (170), These isomeric compounds readily undergo a Claisen rearrangement to afford the second product (171) isolated from the initial irradiation. 

Photochemical decomposition of malonic acid by irradiation in solution has been reported. Some of the radical species produced by this treatment are identical to those formed by the Ce decomposition of malonic acid in the Belousov-Zhabotinsky reaction. The (2 + 2)-cycloadducts (172) can be readily prepared by irradiation of mixtures of the corresponding enone and alkene, and these adducts can conveniently be converted into the hydroperoxide (173) by irradiation at 366 nm in the presence of air and acridine in toluene.The decarboxylation occurs by a free radical pathway and treatment of the hydroperoxide with dimethyl sulfide brings about formation of the ring-expanded ketones or lactones (174), 

In the presence of alkenes, the reaction may follow a different course, involving alkene insertion after oxidative addition, rather than decarbonylation. This is discussed in Chapter 3, Section 3.2 as a form of CH activation. 

Modern Carbonylation Methods, Kollar, L. (Ed.), Wiley, Chichester, 2008 Colquhoun, H. M. Thompson, D. J. Twigg, M. V. Carbonylation, Plenum, New York and London, 1993. 

L Tzamarioudaki, M. Egnchi, M. J. Org. Chem. 1995, 60, 7078 for further examples, see Ojima, I. Vidal, 

Thermal degradation prior to ionization can cause decarbonylation or decarboxylation of the analyte. Decarbonylation, is observed for a-ketocarboxylic acids and a-ketocarboxylic acid esters, while decarboxylation is typical for p-oxo-carboxylic acids such as malonic acid and its derivatives and di-, tri-, or polycar-boxylic acids. 

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Reductive decarbonylation and decarboxylation can be carried out by (TMSlsSiH using acyl chlorides, phenylseleno esters, or N-hydroxypyridine-2-thione esters. Examples are shown in Reactions (17)-(19). Hydrolysis of the methyl ester followed by decarbonylation at the C2 position of hexahydropyrro-loindole (+)-17 afforded the desired tricycle (+)-18 in 84% yield and >99% ee. ... 

Further theoretical study of the mechanism of decomposition of /3-propiolactone and jS-butyrolactone, to form CO2 and ethene or propene, respectively, has concluded that the process can best be described as asynchronous and concerted. Calculations also suggest that concerted processes are preferred for both decarbonylation and decarboxylation of jj-thiobutyrolactone. ... 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

Carbohydrate resources. Carbohydrate resourees, sueh as hydrolyzed stareh and suerose as well as xylose and glueose, ean be proeessed into hydroearbons in a proeess similar to the one performed with bio-oils as described above (section 3.2.2), i.e. by using a HZSM-5 catalyst operated at around 510 °C and ambient pressure." This process is perhaps a little surprising since carbohydrates do not resemble the desired hydrocarbon product as much as the bio-oils do. However, formation of hydrocarbon compounds was found to occur as a result of oxygen removal from the carbohydrate by decarbonylation and decarboxylation reactions." This process is probably one of the first attempts to conduct catalytic cracking of biomass. 

From this scheme it is evident that the hydrodeoxygenation produces a paraffin having the same number of carbon atoms as the fatty acid present in the triglycerides structure, while decarbonylation and decarboxylation produce a paraffin having one carbon atom less than the faty acid present in the triglycerides. 

Maier has reviewed the synthesis of cyclobutadienes, including the photochemical syntheses by decarbonylation and decarboxylation of anhydrides.147 The diones (250a—c) yield the olefins (251) by double decarbonylation on irradiation in methylene chloride.148 Formation of the olefins suggests that the... 

Photolysis of 3-phenyl-5(4H)-isoxazolone yields 2,5-diphenylpyrazine in 67% yield. Singlet excited isoxazol-5-one (224) undergoes both decarbonylation and decarboxylation to carbene intermediates, both of which are captured by alcohol or amine solvents. With triplet sensitisers an oxaziridine intermediate reacts with the solvent. N-Acylisoxazol-5-ones decarboxylate to yield singlet carbenes (225) which cyclise at the acyl oxygen to yield the isoxazoles (227), and the isothiazoles (228) are obtained via thioacyl carbenes (226) from N-thioacylisazol-5-ones. " The isolation of (229) as the main product from irradiation of benzophenone/N,N-dimethylaniline in the presence of the non-polymerising... 

SCHEME 22.16 Ni-catalyzed decarbonylative and decarboxylative cycloaddition of isatoic anhydrides with alkynes. 

Nakai, K., Kurahashi, X, Matsubara, S. (2013). Nickel-catalyzed decarbonylative and decarboxylative cycloaddition of isatoic anhydrides with alkynes. Chemistry Letters, 42, 1238-1240. 

Also obtained by reaction of boiling solution of 1 N sodium hydroxide on methyl 3,5-diacetyl-2,4-dihydroxy-6-methylbenzoate, decarbonylation and decarboxylation occurring simultaneously [2691],... 

I- 2] cycloaddition via heteronickelacycle formation by oxidative addition of heterocyclic substrates to Ni(0), followed by elimination of small molecules such as decarbonylation and decarboxylation [replacement of a part of the heterocyclic molecule with Ni(0)]. 

Other sources for cross-coupling reactions are aldehydes and carboxylic acids after decarbonylation and decarboxylation, respectively, which can be reacted with aryl halides to form biaryls. The following Experimental Procedure illustrates the potential of this quite atom-economic reaction. In this case, a copper co-catalyst promotes both the decarboxylation and the cross-coupling. 

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