Cyclopentanone carbon monoxide

It is assumed that the reaction is initiated by a radical bromine abstraction to give 10-13, which after carbon monoxide insertion undergoes a rapid 5 -exo cycliza-tion onto the hydrazone moiety. The two diastereomeric hydrazinyl cyclopentanones 10-16 and 10-17 are formed with good yields, though with low stereoselectivity. 

Cyclopentanones form from CO and double bonds in 1,5-positions (example 43, Table VII). This is a very selective and stereoselective process, the 1,4- or 1,6-positions being not significantly reactive under the same conditions. o-Hydroxyphenylacetylenes also form 5-membered lactones (example 45, Table VII). In some cases ring closure leads to a new nickel-carbon bond into which a new molecule of carbon monoxide can be inserted. This process of alternative insertion of carbon monoxide and other unsaturated ligands can be repeated several times so that complex alicyclic structures can be formed (example 49, Table VII). This... 

The loss of carbon monoxide from cyclopent-3-enones proceeds much more readily than the loss of carbon monoxide from cyclopropanones and cyclopentanones. 

Smaller-ring ketones, especially cydobutanones and more rigid cyclopentanones or cyclohexanones, give biradicals that follow the fourth of the pathways in which carbon monoxide is not tost. In this process a new oxygen-carbon bond is formed by attack of the oxygen of the acyl radical on the alkyl radical centre this generates a carbene which can subsequently react with a nucleophilic solvent such as methanol (4.28). 

This type of fragmentation has been observed for a number of compounds, most of them having an exocyclic double bond. The decomposition of cyclopentanone (3) into ethene and carbon monoxide was described as a typical example in Section II. Cleavage of y-thiobutyrolactone (54) into carbon monoxide, ethene, and thioformaldehyde [93JCS(P2)1249] was mentioned in Section V.E. Another typical example is the formation of atomic carbon from 5-diazotetrazole (89JA8784). 

Photolysis of cyclopentanone leads to the formation of carbon monoxide, ethylene, cyclobutane (3), and 4-pentenal (28). An early report of the formation of butenes (27) has not been substantiated by later work. The yield of the gaseous products agrees with eq. 1 at 3130 A. and temperatures up to 125° (33) and at shorter wavelengths up to 300° (3). 

It has been observed that the formation of the olefin and carbon monoxide, 45, is ten times more important than the formation of the bicyclic hydrocarbon and carbon monoxide, 46, at 80° and 80 mm. pressure even at 3130 A. The formation of the strained bicyclic hydrocarbon is evidently not a favorable reaction although this may not be the only consideration. In the case of camphor it should be interesting to find out if an optically active isomer of the ketone on photolysis will give rise to an optically active trimethyl bicyclo [2.1.1] hexane (XXVI). A concerted reaction, analogous to the formation of cyclobutane from cyclopentanone, may lead to only an optically active product. 

Compound 1 exhibits significantly different reactivity than the acyclic analogue. The metallacycle is more stable than the acyclic complex and whereas Cp2Ti"Bu2 decomposes via the expected (3-1I elimination pathway to produce butenes and butane, the thermal decomposition products of 1 are ethylene and 1-butene. In addition, the metallacycle is observed to be significantly more reactive towards CO than Cp2Ti"Bu2 Reaction of 1 with carbon monoxide at —55 °C yields the titanium acyl species, based on infrared data, which then rapidly converts to cyclopentanone at 0 °C (Scheme l).13... 

Zewail and his co-workers addressed this question in their laboratory and studied the stability of the tetramethylene diradical generated from various precursors in real time. He showed with femtosecond spectroscopy that intermediate product was in fact formed and had a lifetime of 700 fs. Using cyclopentanone as the precursor they have shown that with two photons at 310 nm (pump) carbon monoxide is eliminated through an a-cleavage. 

Rees and Yelland have reported a fascinating elimination of CO2 from nonadjacent carbonyl groups that occurs both on electron impact and thermolysis Eq. (56). Cyclopentanone p5nrolysis is substantially complicated by radical chain reactions.ii > Nonetheless the three most abundant p5n olysis products, ethylene, carbon monoxide and 1-butene are all represented in the six most intense fragment ions in the mass spectrum of cyclopentanone. 

However, palladium and nickel catalyzed versions promise, at the moment, an even wider range of possibilities. The need to maintain the catalytic cycle by continuous regeneration of the zerovalent metal catalyst limits, nevertheless, the functionalizability of the metallated center in the cyclized intermediate. For the same reason, the readily accessible starting materials may contain various functional groups which are compatible with the reaction conditions and which may be of value for the syntheses of complex heterocycles such as alkaloids. Carbon monoxide insertion reactions of the cyclized a-metal intermediates were shown to afford monocyclic methyl carboxylates and/or annulated cyclopentanones (cyclopentenones) with concomitant stereocontrolled formation of up to four carbon-carbm bonds. 

The weakest bond in the aliphatic polyamide chain is said to be that between the carbon atom of the carbonyl and the nitrogen atom of the —NH— function [84], Cleavage of such bonds anywhere within the molecular chain of nylon-6,6 would produce a frE ment that could cyclize to form carbon monoxide and cyclopentanone... 

A particularly useful synthesis of cyclopentanones involves the coupling of an alkene, an alkyne and carbon monoxide in the presence of dicobalt octacarbonyl (equation 17). The reaction proceeds via an al-kyne-cobalt complex (7) and with relatively unreactive alkenes such as cyclopentene it is preferable to synthesize the complex in a separate step. With highly strained alkenes such as norbomadiene, how-... 

The Pauson-Khand reaction is a powerful tool for the synthesis of cyclopentanones, 246, from a>-alkenylacetylenes, 245, and carbon monoxide.176 Enyne cyclization has been catalyzed with nitriles using catalytic (77S-CsH5)2Ti(PMe3)2 95177-179 and other variants have since been discovered where the desired cyclopentenones can be directly prepared from the enyne and CO using (77S-CsHs)2Ti(CO)2 68 (Scheme 33) 176,180-184 Addition of PMe3 to the latter reaction mixture has proved to be beneficial. Stoichiometric reactions established that the initial step in the catalytic cycle is reductive coupling of the alkyne and the olefin to form the titanacycle. Carbon monoxide insertion followed by reductive elimination generates the observed product. 

Cyclic exponents of the same elimination type are of particular interest. Thus, numerous cyclopentanones photolytically decarbonylate to give 1,4-dienes (p. 876 ff. in Ref. 108)). With thujone (194) this [l,2,(3)4]-elimination of carbon monoxide proceeds quantitatively to give 195 109). With silver nitrate the norcaradiene 196 yields 197 (95%)110) apparently regioselectively, and the [l,2,(3)4]-elimination of methanethiol from 198 to give 199 was realized thermally (16%), acid-catalyzed (59%), and photochemiciiily (ca. 5%)105). For the acid-catalyzed reaction (acetic acid, 100 °C) a non-stereospecific process has been proved 105). 

Beside carbon monoxide extrusion acyl radicals formed in a a-cleavage reaction can stabilize by subsequent hydrogen migration. Thus the a-trimethylsilylmethyl substituted cyclopentanone used by L. F. Tietze gives in a clean photochemical reaction the corresponding aldehyde with a vinylsilane moiety in its side chain. 

Nearly quantitative yields are obtained when 1,4-dienes containing a quaternary center at carbon-3 (R = alkyl, aryl, not H) are converted in the presence of rhodium catalysts 13 14. Here double-bond isomerization in the substrate to form conjugated dienes is suppressed. This hydrocarbonylative cyclization of 1,4-dienes with carbon monoxide gives cyclopentanone products with medium to high regio- and stereoselectivities14-17. Thus, the hydrocarbonylative cyclization of 2.3,3-trimethyl-1.4-pentadiene and similar substrates give predominantly the m-producls [turns cis 1 6). 

Cyclopentanone synthesis via [2+2 + 1] cycloaddition of two alkenes and carbon monoxide ... 

Cyclopentanones, Cyclopentenones and Cyclopentadienones via Carbonylative [2 + 2 + 1 Cyclooligomerization of Alkenes and Alkynes with Carbon Monoxide... 

Cyclopentanones and Cyclopentenones via [2 + 2 + 11 Cycloaddition of Allyl Systems with Alkenes or Aikynes and Carbon Monoxide... 

Tetracarbonylnickel and other nickel(O) compounds, as well as palladium complexes, catalyze the [2 + 2 + 1] cycloaddition of allylic systems with alkenes or alkynes and carbon monoxide to form cyclopentanones or cyclopentenones. This reaction type resembles stoichiometric zirconium- and cobalt-mediated [2 + 2 + 1] cycloadditions (vide supra), mechanistically, however, it proceeds via transition metal 7r-allyl complexes. 

Examples of [2 + 2 + 1] cycloadditions with Cj units other than carbon monoxide are also rare. Some cases use alkynes74 or isonitriles75,76,128- 130 as the Cj building block. Thus, similar to the above reported methods which use carbon monoxide, nickc](0)-promoted cycliza-tion of enynes with isonitriles leads to polycycles containing cyclopentanone units with significant stereoselectivity 75,76. 

Aldehydes show an elimination reaction (loss of carbon monoxide, CO), that is not possible with ketones. Butanal, for example, photodissociates to propane and carbon monoxide. Cyclic ketones dissociate to a diradical (41 from cyclopentanone), which then reacts in any of several ways including elimination to ethene or 42 and coupling to cyclobutane. Formation of cyclobutane and ethene is accompanied by expulsion of CO prior... 

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