- A convenient and efficient preparation of β-substituted α-haloenones from diazodicarbonyl compounds
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Rhodium(II)-catalyzed reactions of cyclic diazodicarbonyl compounds with a variety of halides have been examined. With acid halides, β-acyloxy α-haloenones are produced in good yields. With benzyl halides, β-benzyloxy α-haloenones are obtained in good yie
- Lee, Yong Rok,Cho, Bang Sub,Kwon, Hyuk Jin
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p. 9333 - 9347
(2007/10/03)
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- Reactions of a Cyclic Rhodium Carbenoid with Aromatic Compounds and Vinyl Ethers
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Further investigation has been made of the reactions between the cyclic diazo compound 2-diazo-1,3-cyclohexanedione and aromatic heterocycles or vinyl ethers, catalyzed by rhodium carboxylates.The extraordinary reactivity of the carbenoid derived from this diazo compound is shown by its ready reaction with solvents such as dichloromethane, dichloroethane, and fluorobenzene.Detailed investigation of its reactions with furans have shown that steric interactions dominate, both in terms of regioselectivity with unsymmetrical substrates and yield.This reaction provides a useful entry to the furofuran ring system found in a number of naturally-occurring compounds and is formally a 1,3-dipolar cycloaddition.Products of net C-H insertion and with reverse regiochemistry (furofuran ring system) were also detected.With pyrroles and thiophenes, cycloadducts were seen in a few cases, but were generally the exception; C-H insertion products dominate these reactions.Vinyl ethers proved reliable reactants in providing dipolar cycloadducts.The results of this study have been interpreted in terms of four pathways: an initial cyclopropanation would produce a spirocyclic dicarbonyl system that on heterolytic cleavage of one of the two cyclopropane bonds would give a zwitterion.The partitioning of such a zwitterion between ring closure and proton transfer would define the ratio of C-H insertion and dipolar cycloaddition products.Both thermodynamic and stereoelectronic arguments have been advanced to explain the observations and were supported by calculations.
- Pirrung, Michael C.,Zhang, Jiancun,Lackey, Karen,Sternbach, Daniel D.,Brown, Frank
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p. 2112 - 2124
(2007/10/02)
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- REARRANGEMENT OF 2-ACYL-2-CHLORO-1,3-CYCLOHEXANEDIONES INTO 2-ACYLRESORCINOLS AND 2-ACYL-4-CHLORO-1,3-CYCLOHEXANEDIONES
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2-Acetylresorcinol was prepared in 80-88percent yield from 2-acetyl-1,3-cyclohexanedione by 2-chlorination (excess of NCS in boiling carbon tetrachloride or one equivalent of molecular chlorine in the cold solvent) followed by aromatization in a heated dry solution of hydrogen chloride in dimethylformamide.The scope of the method was extended to the preparation of 2-propionyl- and 2-isobutyrylresorcinol (resp. 79percent and 66percent yield).Application of the method on 2-acryl-5,5-dimethyl-1,3-cyclohexanediones (acyl=acetyl, propionyl, n-butyryl, i-butyryl) affrded the corresponding 2-acyl-4-chlorodimedone derivatives in 40-77percent yields.
- De Buyck, L.,Seynaeve, D.,De Kimpe, N.,Verhe, R.,Schamp, N.
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p. 363 - 370
(2007/10/02)
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