A Novel Carbonylation Method Based on the Free-Radical Reaction of Carbon Monoxide.
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Abstract:
A novel carbonylation method based on free-radical reactions has been developed. Acyl radicals, generated by the addition of alkyl free-radicals to carbon monoxide, have been effectively trapped by tin hydride. Through this sequence, the free-radical formylation of organo halides to the corresponding aldehydes was realized. Carbonylative cyclizations to give cyclopentanones can also be affected starting with 4-pentenyl halides. When an alkene was also present in the reaction system, the trapping of the alkyl free-radical by carbon monoxide to form an acyl free-radical and the subsequent addition of that radical to the alkene took place efficiently to give an unsymmetrical ketone. This sequence represents a unique method for the double alkylation of carbon monoxide β, γ-Unsaturated ketones can be synthesized via a three-component coupling of alkyl iodides, carbon monoxide, and allylstannane. All of these findings have demonstrated that free-radical carbonylation is a useful method for the introduction of carbon monoxide into organic molecules.Keywords:
Carbonylation
Alkene
Tributyltin hydride
s-Butyl, 3-hexyl, cyclopentyl, and cyclohexyl t-butyl peroxides have been prepared in yields of 63, 24, 59, and 61%, respectively, by reducing with tributyltin hydride the peroxymercurials derived from the corresponding symmetrical alkenes.
Tributyltin hydride
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A novel carbonylation method based on free-radical reactions has been developed. Acyl radicals, generated by the addition of alkyl free-radicals to carbon monoxide, have been effectively trapped by tin hydride. Through this sequence, the free-radical formylation of organo halides to the corresponding aldehydes was realized. Carbonylative cyclizations to give cyclopentanones can also be affected starting with 4-pentenyl halides. When an alkene was also present in the reaction system, the trapping of the alkyl free-radical by carbon monoxide to form an acyl free-radical and the subsequent addition of that radical to the alkene took place efficiently to give an unsymmetrical ketone. This sequence represents a unique method for the double alkylation of carbon monoxide β, γ-Unsaturated ketones can be synthesized via a three-component coupling of alkyl iodides, carbon monoxide, and allylstannane. All of these findings have demonstrated that free-radical carbonylation is a useful method for the introduction of carbon monoxide into organic molecules.
Carbonylation
Alkene
Tributyltin hydride
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Abstract AIBN‐initiated radical reactions of 5‐membered cyclic xanthates, 1,3‐oxathiolane‐2‐thiones, with tributyltin hydride are described. Alkenes are formed at 0.025 M concentration of tributyltin hydride, whereas a higher concentration (0.25 M) gives 1,3‐oxathiolanes. A mixture of alkene and 1,3‐oxathiolane is obtained by use of intermediate concentrations. Reactions of cis‐and trans‐4,5‐dialkyl‐1,3‐oxathiolane‐2‐thiones with tributyltin hydride afford E‐alkenes stereoselectively. For an application of this alkene formation reaction, geraniol has been converted to linalool silyl ether in good yield.
Tributyltin hydride
Alkene
Silyl ether
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The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.
Carbonylation
Moiety
Pauson–Khand reaction
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Alkene
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Carbonylation chemistry (carbon monoxide chemistry) has been the subject of extensive research in labo-scale organic syntheses as well as industrial processes, since it provides a powerful tool for the direct synthesis of a wide variety of carbonyl-containing compounds. However, the methods suffer from major disadvantages, including the high toxicity of carbon monoxide and difficulties in handling this gaseous reagent. The review describes innovative strategies to solve these drawbacks. The strategies should provide many synthetic organic chemists with experimentally simple and safe tools for carbonylation.
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Monoxide
Organic Synthesis
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5,10-Diphenylcyclotrideca-2,4,10,12-tetraene-6,8-diyn-1-one (28), 5,6,7,8-tetrahydrodibenzo[a,g]cyclotridecen-15-one (21), and 13,14,16,17-tetrahydro-5,6,7,8-tetradehydrodibenzo[a,g]cyclotridecen-15-one (40) were synthesized. All attempts to add hydrogen sulphide across the triple bonds of these compounds to give thiophenes failed. 13,14,16,17-Tetrahydro-5,8-epithiodibenzo[a,g]cyclotridecen-15-one (43), from which hydrogen sulphide was removed by DDQ or chloroanil to give the ketone (40), was synthesized via the copper(II) acetate oxidation of 1,5-bis(2-ethynylphenyl)pentan-3-one (36). This ketone was obtained from 2-iodobenzaldehyde which on successive treatment with acetone, and ethynyltrimethylsilane yielded 1,5-bis(2-trimethylsilylethynylphenyl)penta-1,4-dien-3-one (18). Tributyltin hydride reduced the vinyl double bonds only in this ketone, and subsequent hydrolysis gave the ketone (36). Reduction of the, cyclic ketone (40) with sodium borohydride gave the alcohol (41), sodium sulphide converted the diyne grouping into a thiophene ring giving the thiophene alcohol (42), and chromic acid now yielded the ketone (43). Attempts to convert this alcohol (42) and ketone (43) into pentacyclic sulphonium salts or related compounds resulted in elimination of oxygen and the formation of olefins.
Sodium borohydride
Tributyltin hydride
Methyl vinyl ketone
Triple bond
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Nickel seems one of the most promising transition metals as a catalyst for a variety of carbonylation reactions. In fact, it has played an important role in industrial usage. However, a limited number of the catalytic carbonylation reactions have been reported. One of the reasons why chemists would not develop nickel-catalyzed carbonylation reactions is due to the possibility of the formation of the notorious highly toxic Ni(CO)4 in situ, which indicates that nickel can react with carbon monoxide. In this chapter, formation of nickelacycles and their reactivity with carbon monoxide to give cyclic carbonyl compounds are introduced.
Carbonylation
Reactivity
Monoxide
Nickel compounds
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Tributyltin hydride
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Abstract Progress in organometallic catalysis began with the discovery of the Roelen reaction (hydroformylation with carbon monoxide and hydrogen) in 1938 and the Reppe reaction (hydrocarboxylation with carbon monoxide and water) in 1939. Since then, carbonylation chemistry by using carbon monoxide has occupied a central position in organometallic chemistry, as it relates to organic synthesis. There is, however, the problem of using gaseous carbon monoxide (a toxic greenhouse gas) in this chemistry. Recently, some strategies that address this issue have appeared. This minireview describes carbonylation reactions that can be conducted without the direct use of carbon monoxide. These carbonylation reactions provide reliable and accessible tools for synthetic organic chemists.
Carbonylation
Organometallic Chemistry
Monoxide
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