- Is a phase transfer catalyst really needed for gem-dihalocyclopropanation of alkenes with haloforms in the presence of alkali metal hydroxide?
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Chloroform, bromoform and dibromochloromethane react with alkenes in the presence of cone. aq. sodium hydroxide, without phase-transfer catalyst, giving gem-dihalocyclopropanes. The process is particularly useful for preparation of gem-bromochlorocyclopropanes which are formed in good yields and in high selectivity.
- Karwowska,Jonczyk
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- The nickel and palladium catalyzed stereoselective cross coupling of cyclopropyl nucleophiles with aryl halides
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The reaction of 2-phenylcyclopropylzinc chloride with some substituted (het)aryl halides gave the corresponding coupling products with good yields and stereoselectivities under the influence of a catalytic amount of Pd(PPh3)4. Other Ni- and Pd-catalysts were less efficient. Alkyl-substituted cyclopropyl nucleophiles gave lower yields.
- De Lang,Brandsma
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p. 225 - 232
(2007/10/03)
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- Photochemical activation of metalloporphyrin carbene complexes
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While the photochemistry of simple metalloporphyrin complexes has been explored to some extent, the photoactivation of multiple-bonded axial ligands coordinated to metalloporphyrins has not been previously examined. We report here the photochemistry of several iron porphyrin carbene and vinylidene complexes. Irradiation of these complexes with visible light cleaves the iron-carbon double bond and produces a four coordinate iron(II) porphyrin and a free carbene, which can be trapped in high yield with a variety of alkenes. This photochemistry is unique among organo transition metal complexes of carbenes or alkylidenes. For these metalloporphyrin carbene complexes, the presence of the porphyrin ring alters the photoreactivity of the metal-carbon bond. This is probably due to the mixing between the π * orbitals of the porphyrin ring and the iron-carbon orbitals, which is also responsible for the hypso-type spectrum (i.e. blue-shifted) seen in these complexes. Hypso spectra are a common trait in other photodissociative porphyrin complexes, most notably CO complexes.
- Ziegler, Christopher J.,Suslick, Kenneth S.
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- PREPARATION OF ALLYL ALCOHOLS FROM MONOHALO- AND GEM-DIHALOBUTYLCYCLOPROPANES IN THE PRESENCE OF COPPER AND ITS SALTS
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The reaction of gem-dibromo- or gem-dichlorobutylcyclopropanes with an equimolar amount of CuSO4*5H2O in a mixture of DMSO and water is accompanied by scission of the three-membered ring and formation of the corresponding 2-bromo- or 2-chloroallyl alcohols.The corresponding allyl alcohols were prepared analogously from monobromo- or monochlorocyclopropanes.
- Korneva, O. S.,Nefedov, O. M.
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p. 2194 - 2196
(2007/10/02)
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- ELECTROCHEMICAL OXIDATION OF ALKYL-SUBSTITUTED ALLENES IN METHANOL
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Mono-, di- and tri-alkyl-substituted allenes were potentiostatically oxidized in methanol at graphite and Pt anodes.At the former electrode, α-methoxylated ketones (due to 4F/mole electricity consumption) and esters (6F/mole) were the major products.At a Pt anode, intermediate products such as vinyl-ether derivatives (2F/mole) were characterised too.Unlike the anodic oxidation of alkenes and alkynes previously reported in the literature, dimerisation is not a typical process in the allenes' oxidation, since of all the products obtained only a sole dimer has been observed.The mechanism for the formation of most products is discussed.
- Becker, James Y.,Zinger, Baruch
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p. 1677 - 1682
(2007/10/02)
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