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5 article(s) from Yamabe, Shinichi

Proton transfers in the Strecker reaction revealed by DFT calculations

Shinichi Yamabe,
Guixiang Zeng,
Wei Guan and
Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 1765–1774, doi:10.3762/bjoc.10.184

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Scheme 1: The general form of the Strecker reaction. The reaction (b) is taken from [2].

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Scheme 2: The first asymmetric Strecker reaction [4].

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Scheme 3: The first asymmetric synthesis of α-aminonitirles via a chiral catalyst [5].

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Scheme 4: A reaction model composed of Me-CH=O, HCN, NH₃ and (H₂O)₁₀ for geometry optimizations to trace elem...

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Scheme 5: Possible pathways for the formation of aminonitrile from acetaldehyde.

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Figure 1: Geometries of transition states along the reaction from acetaldehyde (1) to the aminonitrile 8. Dis...

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Figure 2: Energy changes along elementary processes from acetaldehyde to aminonitrile. Bold numbers are defin...

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Scheme 6: A short-cut path by the nucleophilic displacement and the concomitant proton transfer. “The first b...

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Scheme 7: A contrast of the nucleophilic addition.

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Figure 3: Two transition states (A and B) of the nucleophilic addition of (S)-α-phenylethylamine to acetaldeh...

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Scheme 8: Elementary processes of the acid-catalyzed hydrolysis of 2-amino-propanonitrile.

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Figure 4: Energy changes along elementary processes from 2-amino nitrile 8 to 2-amino acid 16. Brown-color li...

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Figure 5: Geometries of transition states along the most favorable route from 2-aminonitrile 8 to 2-amino aci...

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Scheme 9: Summary of the present computational work expressed by minimal models.

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Published 01 Aug 2014

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Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

Shinichi Yamabe,
Guixiang Zeng,
Wei Guan and
Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 259–270, doi:10.3762/bjoc.10.21

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Scheme 1: The Wolff–Kishner (W-K) reduction. DEG, diethylene glycol (HO–C₂H₄–O–C₂H₄–OH), is usually used as a...

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Scheme 2: Mechanism of the Wolff–Kishner reduction. The route (a) is taken from ref. [6] and (b) from refs. [5,7,8].

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Scheme 3: An uncatalyzed (without base) Knoevenagel condensation in water. Experimental conditions and yields...

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Scheme 4: Reaction models of neutral (a) and anionic (b) systems. Water molecules are linked to oxygen lone-p...

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Figure 1: Geometric changes of the neutral Wolff–Kishner reduction reaction. The employed model is shown in Scheme 4a ...

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Scheme 5: A CT complex between R¹R²C=O and H₂N–NH₂ assisted by two hydrogen networks. R³–OH is an alcohol mol...

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Figure 2: Energy changes of the neutral W-K reaction of acetone. Geometric changes are shown in Figure 1 and Figure S...

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Figure 3: Geometric changes of the base-promoted Wolff–Kishner reduction reaction. The model employed is show...

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Figure 4: Energy changes of the OH⁻ containing W-K reaction of acetone calculated by B3LYP/6-311+G**. Geometr...

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Scheme 6: The main part of TS6. The N1···H26 hydrogen bond is converted into the C1–H26 covalent bond.

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Figure 5: A trans-diimine → propane conversion step corresponding to TS6 in Figure 3. The system is composed of trans...

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Figure 6: Geometric changes of the base-promoted Wolff–Kishner reduction reaction of acetophenone [Me–C(=O)–P...

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Figure 7: Energy changes of the OHˉ containing W-K reaction of acetophenone. Geometric changes are shown in Figure 6....

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Scheme 7: Elementary processes of the W-K reduction obtained by DFT calculations. From the diimine intermedia...

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Published 23 Jan 2014

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An aniline dication-like transition state in the Bamberger rearrangement

Shinichi Yamabe,
Guixiang Zeng,
Wei Guan and
Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 1073–1082, doi:10.3762/bjoc.9.119

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Scheme 1: The Bamberger rearrangement. In the square bracket, the apparent exchange of H and OH is shown.

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Scheme 2: The reaction occurs through the intermolecular rearrangement, on the basis that treatment of 1 in H₂...

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Scheme 3: A reaction of N-ethyl-N-phenylhydroxylamine, which demonstrates that the Bamberger rearrangement do...

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Scheme 4: A mechanism involving the nitrenium-ion intermediate 7. 8a is equal to 6.

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Scheme 5: A reaction scheme of the OH rearrangement containing one proton. Int is an intermediate. Species, 1...

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Figure 1: Geometric changes in the reaction of model II, (HO)HN–C₆H₅ + H₃O⁺(H₂O)₁₄ → H₃N⁺–C₆H₄–OH + (H₂O)₁₅.

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Figure 2: An assumed reaction system composed of Ph–NHOH and H₃O⁺(H₂O)₁₄. The green area represents the react...

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Figure 3: Energy changes (in kcal/mol) of Δ(E+ZPE) by B3LYP/6-311+G(d,p) SCRF = PCM//B3LYP/6-31G(d) and by [B...

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Scheme 6: A trans-type bond interchange was assumed. But, the reaction path could not be obtained. The group ...

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Scheme 7: An alternative model for the OH [1,5]-rearrangement in the dication system.

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Figure 4: Geometric changes in the reaction of model III, (HO)HN–C₆H₅ + (H₃O⁺)₂(H₂O)₁₃ → H₃N⁺–C₆H₄–OH + (H₃O⁺...

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Figure 5: Energy changes (in kcal/mol) of model III. The corresponding geometries are shown in Figure 4. The apparent...

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Figure 6: TS2(IV) and TS2(IV, [1,3]-shift) in the reaction (model IV), Ph–NH(OH) + (H₃O⁺)₂(H₂O)₂₄ → HO–C₆H₄–NH...

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Figure 7: TS2(V) and TS2(V, [1,3]-shift) in the reaction (model V), Ph–NH(OH) + (H₃O⁺)₂(H₂O)₁₃ + Cl⁻ → o- and ...

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Scheme 8: A mechanism of the Bamberger rearrangement based on the present results. 1, 2, 2H⁺, 5 and 9 are def...

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Published 03 Jun 2013

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A new intermediate in the Prins reaction

Shinichi Yamabe,
Takeshi Fukuda and
Shoko Yamazaki

Beilstein J. Org. Chem. 2013, 9, 476–485, doi:10.3762/bjoc.9.51

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Scheme 1: A general scheme of the Prins reaction.

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Scheme 2: An example of the Prins reaction [4]. The product yields (%) are based on formaldehyde.

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Scheme 3: An equilibrium in the hydrolysis of the product, 1,3-dioxane.

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Scheme 4: Formation of the acetate of an allylic alcohol by Prins reaction [5].

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Scheme 5: A reaction mechanism involving the carbonium-ion intermediate X.

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Scheme 6: A reaction model composed of RHC=CH₂, (H₂C=O)₂ and H₃O⁺(H₂O)₁₃ to obtain the path of step 2 (Scheme 5). H₃O⁺...

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Figure 1: Geometries of the precursor and the transition states (TSs) of the Prins reaction of propene with (...

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Figure 2: Energy changes (in kcal/mol) of the propene Prins reaction calculated by B3LYP/6-311+G(d,p) SCRF=(P...

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Figure 3: Geometries of the transition states (TSs) of the Prins reaction of styrene + (formaldehyde)₂ + H₃O⁺...

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Figure 4: Energy changes (in kcal/mol) of the styrene Prins reaction calculated by B3LYP/6-311+G(d,p) SCRF = ...

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Figure 5: TS1(Ph) geometries of n = 20 and n = 30 in the reacting system of styrene + H₃O⁺(H₂O)_n + (H₂C=O)₂ c...

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Scheme 7: Summary of the present calculated results. The ether in the box is the new intermediate found in th...

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Published 05 Mar 2013

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Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

Shinichi Yamabe,
Wei Guan and
Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 185–196, doi:10.3762/bjoc.9.22

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Scheme 1: A scheme of the base-catalyzed amide hydrolysis involving a zwitterion suggested by analyses of sol...

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Scheme 2: Two processes suggested by a proton-inventory NMR study [25].

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Scheme 3: Hydrolysis of the ester (saponification) and the amide adopted in this work. These are assigned as ...

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Scheme 4: A reaction model including the water cluster.

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Figure 1: A minimal model of the OH⁻ nucleophilic addition to the substrate, Ph–C(=O)–X–Et. Three ((a), (b) a...

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Figure 2: Geometries and B3LYP/6-31(+)G(d) activation energies of TS1(es) in the reaction between ethyl benzo...

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Figure 3: Geometries and activation energies of TS1(am) in the reaction between N-ethylbenzamide and OH^-(H₂O)_n...

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Figure 4: Reaction paths of the ester n = 16 hydrolysis, starting from the boxed reactant-like complex toward...

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Scheme 5: A possibility that the neutral tetrahedral intermediate is the stock of concentrations for the irre...

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Figure 5: Reaction paths of the amide n = 16 hydrolysis. XYZ coordinates in VII.d (Supporting Information File 1).

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Figure 6: Changes of B3LYP/6-311++G(d,p) SCRF = PCM//B3LYP/6-31(+)G(d) Et + ZPE and (Gibbs free energies) of ...

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Figure 7: The effect of the counter ion Na⁺ on TS1(es). When the position of Na⁺ is near the nucleophile OH⁻ ...

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Figure 8: Changes of Et + ZPE and (Gibbs free energies) of the amide hydrolysis in Figure 5 and Figure S4 (Supporting Information File 1). Energie...

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