- Diazoaldehyde Chemistry: Part 4 - Vilsmeier-Haack Formylation of Diazo Compounds: A Re-investigation
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Diazomethyl ketones (2-diazoethanones) were reacted with the Vilsmeier reagent ((chloromethylidene)dimethylammonium chloride) to yield α-diazo-β-oxoaldehydes and chloromethyl ketones. 2′,4′-Dimethoxy-α-diazoacetophenone gave 2-chloro-1-(2,4-dimethoxyphenyl)-3-(dimethylamino)prop-2-en-1-one (5) in addition to the expected products. Phenyldiazomethanes gave the corresponding benzyl chlorides but not the (phenyl)diazoacetaldehydes even at temperatures as low as -60°. The diazo-transfer reactions of phenylacetaldehydes and 2-azido-1-ethylpyridin-1-ium tetrafluoroborate also did not yield the expected(phenyl)diazoacetaldehydes.
- Sezer, Oezkan,Dabak, Kadir,Anac, Olcay,Akar, Ahmet
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- Expeditious synthesis of 2,3,6-trisubstituted 2 H -1,3-oxazin-4(3 H)-ones via the tertiary amine-induced reaction of 2-diazo-3-oxoalkanals and imines under mild conditions
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A series of 2,3,6-trisubstituted 2H-1,3-oxazin-4(3H)-one derivatives were conveniently synthesized in satisfactory to good yields by the reaction of imines with 2-diazo-3-oxoalkanals in the presence of a catalytic amount of a tertiary amine during several seconds under mild condition. Different bases and -diazo - dicarbonyl compounds were also evaluated and a reaction mechanism is proposed. Compared with the corresponding thermal- and photo-induced- reactions, the current method is a metal-free, mild, highly regioselective, and more efficient approach for the synthesis of 2H-1,3-oxazin-4(3H)-one derivatives. Georg Thieme Verlag Stuttgart - New York.
- Qi, Hengzhen,Zhang, Jiantao,Xu, Jiaxi
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supporting information; experimental part
p. 887 - 894
(2011/05/05)
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- Stereoselective control in the Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents: Experimental investigation and theoretical rationalization
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The stereoselectivity of the Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents was investigated experimentally by determination of the product stereochemistry and theoretically via DFT calculations. The results indicate that imines preferentially attack the less sterically hindered exo-side of the ketenes to generate zwitterionic intermediates. Subsequently, for cyclic imines, the intermediates undergo a conrotatory ring closure directly to produce β-lactams, while for linear imines, the imine moiety of the intermediates isomerizes to more stable intermediates, which further undergo a conrotatory ring closure to afford trans-β-lactams. The steric hindrance and the isomerization, rather than the torquoelectronic effect, play crucial roles in controlling the stereoselectivity in the practical Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents, although the unaccessible borylketene with a powerful electron acceptor group controls the stereoselectivity torquoelectronically, in theory.
- Qi, Hengzhen,Li, Xinyao,Xu, Jiaxi
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supporting information; experimental part
p. 2702 - 2714
(2011/05/19)
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- 40. Diazoaldehyde chemistry: Part 3. Synthesis of 4-acyl-1H-1,2,3-triazole derivatives
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Ten new α -diazo-β-oxoaldehydes were condensed with aniline, ammonia, hydroxylamine, and semicarbazide to yield new 4-acyl-(1-substituted)-1H-1,2,3-triazoles in moderate-to-good yields. The method is simple and regiospecific. The latter feature makes this method superior to the widely used acylacetylene + azide approach.
- Sezer, Oezkan,Dabak, Kadir,Akar, Ahmet,Anac, Olcay
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p. 449 - 453
(2007/10/03)
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- Diazoaldehyde Chemistry. Part 1. Transdiazotization of Acylacetaldehydes in Neutral-to-Acidic Medium. A Direct Approach to the Synthesis of α-Diazo-β-oxoaldehydes
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First ever non-deformylating transdiazotization of acylacetaldehydes was achieved: the reactions of 2-azido-1-ethylpyridinium tetrafluoroborate (4) with acylacetaldehydes 3 proceeded partially without deformylation to yield 16 new α-diazo-β-oxoaldehydes 1 along with diazomethyl ketones 2, especially in the presence of NaOAc (Scheme 1, Tables 1 and 2).The product distribution was substituent-dependent and could be correlated quantitatively.This new diazotization reaction appears as an alternative, direct, and more general method for the synthesis of these diazooxoaldehydes. α-Oxocycloalkanecarbaldehydes 5 gave only traces (if any) of α-diazocycloalkanones 7, and rearrangement products 6 were isolated (Scheme 2).Mechanisms of the reactions are discussed (Schemes 4 and 5).
- Sezer, Oezkan,Anac, Olcay
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p. 2323 - 2334
(2007/10/02)
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