- Chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal with aldehydes and ketones
-
The chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal (1) with aldehydes and ketones in the presence of Et3N was investigated. The results indicate that 1 reacts with aromatic aldehydes with weak electron-donating substituents and cyclic ketones under formation of 6-phenyl-4H-1,3-dioxin-4-one derivatives. However, it reacts with aromatic aldehydes with electron-withdrawing substituents to yield 1,3-diaryl-3-hydroxypropan-1-ones, accompanied by chalcone derivatives in some cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong electron-donating substituents. A mechanism for the formation of 1,3-diaryl-3-hydroxypropan-1-ones and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds, including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N′-dialkylcarbodiimines, phenyl isocyanate, isothiocyanate, and CS2. Only with N,N′-dialkylcarbodiimines, the expected cycloaddition took place. Copyright
- Zhang, Jiantao,Xu, Jiaxi
-
p. 1733 - 1739
(2013/10/21)
-
- Stereoselective control in the Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents: Experimental investigation and theoretical rationalization
-
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
-
p. 2702 - 2714
(2011/05/19)
-
- 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
-
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
-
supporting information; experimental part
p. 887 - 894
(2011/05/05)
-
- Diazoaldehyde Chemistry. Part 1. Transdiazotization of Acylacetaldehydes in Neutral-to-Acidic Medium. A Direct Approach to the Synthesis of α-Diazo-β-oxoaldehydes
-
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
-
p. 2323 - 2334
(2007/10/02)
-