- Zinc-promoted reactions. Part 5. The behaviour of alkyl substituted 1,3-diketones
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The zinc-promoted reaction of 2,4-pentanedione and related β-dicarbonyl substrates have been investigated under a variety of conditions. The results were explained according to a general mechanism, involving ionic and nonionic pathways.
- Floris, Barbara,Luchetti, Luciana,Rosnati, Vittorio
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p. 4409 - 4418
(2007/10/02)
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- Photochemistry in solution-XX. Triplet reactivity of aliphatic aldehydes
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The triplet self-quenching process of three aliphatic aldehydes has been investigated by inhibition with dienes (taking into account the singlet interaction with the dienes) and by laser flash photolysis. The results obtained for intersystem crossing, the setf-quenching process and product formation have been rationalized. The main reactivity observed for the three aldehydes is the self-quenching process which occurs from both the singlet and triplet state. The laser flash photolysis experiments carried out with butanal show two absorptions of a transient at 320 aod 355 nm; no evidence for two different species could be put forward. The similar decay of the two absorption maximas of the transient, as the concentration of aldehyde is increased, would be indicative of only one single absorbing species which could be either the triplet state of the aldehyde or a radical-pair formed by the self-quenching process or the 1,4-biradical resulting from γ-H abstraction. The fact that both the quenching experiments (by dienes or by 1-methylnaphthalene) and the laser flash measurements lead to about the same lifetime also indicates only one species. The products formed from the triplet setf-quenching process have also been obtained by a different method: excitation of benzophenone at 365 nm in the presence of butanal. The quantum yields for product formation is about the same as those obtained for the triplet by direct irradiation of butanal, except that of octane-4,5-dione which is increased if the photoreaction is carried out at 365 nm in the presence of beazophenone.
- Kossanyi,Sabbah,Chaquin,Ronfart-Haret
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p. 3307 - 3315
(2007/10/02)
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- Chemistry of O-Alkyl Selenoesters. Reaction with Triethylphosphine
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The reaction between triethylphosphine and a number of aliphatic and aromatic selenoesters under oxygen-free conditions have been investigated.The purple intermediate formed in the reaction with the aliphatic selenoesters was quenched with atmospheric oxygen and gave the corresponding esters, whereas quenching with methyl iodide gave the corresponding 1-alkoxy-1-iodoalkyltriethylphosphonium iodides (13)-(16).The 1-alkoxy-1-iodoalkyltriethylphosphonium iodides gave the 1-alkoxyalkyltriethylphosphonium iodides (17)-(20) upon treatment with methanol, and treatment with benzaldehyde at -70 deg C gave α-alkoxyalkyl phenyl ketones (22)-(25).The reaction between the selenobenzoates and triethylphosphine gave α-dialkoxy-stilbenes and -dibenzyls.When the reaction was carried out in cyclohexene 7-alkoxy-7-phenylbicycloheptanes were formed.The presence of benzaldehyde in the reaction mixture led to α-alkoxystilbenes.An explanation for these different reactions is presented.
- Hansen, Per-Egil
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p. 1627 - 1634
(2007/10/02)
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