Decarbonylation photochemical

Decarbonylation, photochemical 885 Decarboxylation 605 Dehydrohalogenation 417 n-Delocalization 392 Demeton sulphones, mass spectra of 155... 

Photo-decarbonylation of the cyclohexanone (32a) is efficient with a quantum yield of 0.9. The reaction yields the two products (33) and (34) in a ratio of 1 2. The cyclopentanone (32b) also decarbonylates photochemically but is less efilcient with a quantum yield of 0.5. A laser flash study has been carried out on these systems and has identified the biradicals produced by the Norrish type I process. The lifetime of the biradicals (35a) and (35b) are O.Ojxs and 0.5 xs respectively. In a related study the photodecarbonylation of cIs- and frans-2,6-diphenylcyclo-hexanone has been shown to yield a mixture of cis- and 2-diphenyl-cyclopentane and cIs- and... 

Reaction of hexa-2,4-diyne with Fe(CO)6 yields the cyclopentadienone complex (108), characterized crystallographically. Reaction of Fe(CNBu )6 with PhC=CPh yields (109), characterized crystallographically. The ion HFe(CO)4 reacts with acetylenes HC=CCOR to yield products of structure (110), although a crystal structure determination indicates some contribution from a -olefin- -acyl structure. Protonation of (110) yields Fe[t -HRC=C(H)(COR)](CO)4 via an intramolecular decarbonylation. - Photochemical reaction between... 

Ketenes decarbonylate photochemically to carbenes which may give rise to olefinic end groups by hydrogen transfer. 

The bridged radical A has been suggested as a possible intermediate in the photochemical decarbonylation of 3-phenylpropanal. Suggest an experiment to test this hypothesis. 

Irradiation at 20 C of perfluoro ethers containing a carbonyl group causes almost quantitative decarbonylation [179. Azindine undergoes photochemical addition with methyl trifluoroacetate [180 (equation 47). 

Carbonyl compounds can undergo various photochemical reactions among the most important are two types of reactions that are named after Norrish. The term Norrish type I fragmentation refers to a photochemical reaction of a carbonyl compound 1 where a bond between carbonyl group and an a-carbon is cleaved homolytically. The resulting radical species 2 and 3 can further react by decarbonylation, disproportionation or recombination, to yield a variety of products. 

Photochemical decarbonylation of CpFe(CO)2 COMe has now been shown to afford CpFe(CO)( CO)Me which is consistent with loss of a terminal CO [J. J. Alexander, private communication (April 1972)]. 

There has been only one study concerned with stereochemical changes at an asymmetric metal. It dealt with the photochemical decarbonylation 208) ... 

Figure 7.24. Solid-state photochemical decarbonylation model for ketones. The dashed path corresponds to the experimentally determined energies of acetone (in kcal/mol). The effects of substituents with radical stabilizing energies (RSEs) are illustrated by the solid line in the reaction coordinate. See color insert.

Figure 7.25. Scheme of the photochemical decarbonylation of 67 and 69 in the solid state, showing their respective ORTEP representation from X-ray data below the ChemDraw strnctnre. 

Chapman, O. L. McIntosh, C. L. Photochemical decarbonylation of unsaturated lactones and carbonates. J. Chem. Soc., Chem. Commun. 1971, 383-384. 

Two of the three general types of secondary reactions resulting from photochemical a-cleavage of carbonyls, namely molecular rearrangement and hydrogen transfer to yield aldehydes or ketenes, have been discussed. The third type of reaction observed, decarbonylation, will be discussed in this section. The discussion will begin with the decarbonylation of small ring carbonyls. By way of example of this type of reaction, diphenylcyclopropenone decarbonylates upon photolysis to yield diphenylacetylene(57) ... 

Photochemical excitation results in a-cleavage to produce a primary, geminate radical pair, which may undergo radical combination reactions (1) in competition with decarbonylation or (2) to produce a secondary geminate radical pair. The latter may undergo radical combination (3) or produce a free-radical pair (4). The free radicals undergo radical combination reactions (5). 

Alexander, J.J. Mechanism of Photochemical Decarbonylation of Acetyldicar-bonyl-r -Cyclopentadienyliron. J. Am. Chem. Soc. 1975, 97, 1729-1732. 

If photochemical apparatus is not available, the cycloisomerization reaction can be conducted using trimethylamine N-oxide to promote oxidative decarbonylation of molybdenum hexacarbonyl in a mixture of EtjN and EtgO, followed by addition of 1-phenyl-3-butyn-1-ol (1). In the submitters hands, this procedure required somewhat higher loading of molybdenum hexacarbonyl, and purification of the 2-phenyl-2,3-dihydrofuran (2) product required silica gel chromatography. 

Compounds of type 43 and 44 tend to undergo radical cleavage readily. Carbonyl radicals formed are relatively stable and do not decarbonylate provided that an aromatic nucleus in the -position exerts a stabilizing effect. Minimal amount of by-products were observed when at least one of the substituents Rx or R2 was phenyl. The photochemical conversion 43 44 is... 

Few substituted cymantrene derivatives have been investigated for their photochemical behavior, and whether decarbonylation will always be the preferred path is unknown. Cuingnet and Adalberonj- attributed, without... 

On the other hand there are certain groups of reactions that have been neglected so far, among them the photochemical behavior of the gera-dihalocyclopropanes. One of the few reported examples is by Weyerstahl who has attempted to generate hexachloro-tris-CT-homobenzene from the corresponding tris-a-homocyclo-heptatrienone [233], The latter, however, prefers to undergo trans-cis isomerization rather than decarbonylation. 

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