Evidence for the Amino–Claisen rearrangement occurring in the molecular ions of N-allylaniline

One of the most intense peaks in the mass spectrum of N-allylaniline is at m/z 106 (97%). High resolution analysis and collision-induced dissociation studies confirm that this peak contains mostly [C₇H₈N]⁺ ions having the anilinomethene structure, but also a small contribution is seen from [C₈H₁₀]⁺ ions which result from the loss of the elements of HCN from molecular ions, following an Amino–Claisen rearrangement. The occurrence of a thermal rearrangement in the sample molecules cannot, however, be completely ruled out. Studies on metastable molecular ions of N-allylaniline and collision-induced dissociation of the m/z 106 ions formed from these show that, in the case of molecular ions with energies closer to threshold, the rearrangement reaction competes much more effectively with the direct cleavage reaction.     

A homologous ester claisen rearrangement via the cope rearrangement of O-trimethylsilylcyanohydrins

The Cope rearrangement of 1,5-dienyl trimethylsilyl-cyanohydrins to α-trimethylsilyoxy-α,β-unsaturated nitriles and their cleavage to methyl δ-hexenoates is discussed.     

On the claisen rearrangement of 1,4-diaryloxy-2-butynes

A proton nmr follow-up provided conclusive evidence for the involvement of two sequential Claisen rearrangements in the thermal rearrangement of 1,4-diaryloxy-2-butynes $\text{1}$to 11a-methylpterocarpans $\text{3}$. A detailed study of the rearrangement of 1,4-diaryloxy-2-butynes $\text{1}$ in polyethyleneglycol-200 (PEG-200), indicated a definite possibility of selective synthesis of either benzofuron (3,2-b )benzofuran $\text{4}$ or benzofuro(2,3-b)benzofuran $\text{5}$ by varying the temperature of the reaction alone     

The Claisen rearrangement of protonated allyl phenyl ether

Molecular protonated ions of allyl phenyl ether undergo a Claisen rearrangement both in the ion source and along the flight path. The rearranged ions undergo fragmentation, the predominat loss being ethene, and only a small contribution from loss of carbon monoxide is observed. Collision-induced dissociation spectra are used to verify the structures of the daughter ions. These spectra, together with other evidence of an acid-induced ortho rearrangement, allow a mechanism to be proposed for the ethene loss. In contrast, molecular protonated ions of propargyl phenyl ether lose exclusively carbon monoxide.     

The ester enolate claisen rearrangement of allyl α-hydroxyacetates and α-phenylthioacetates

The ester enolates of allylα-hydroxyacetates and α-phenylthioacetates undergo a Claisen rearrangement to give α-substituted-γ,δ-unsaturated acids.     

Site specificity in the H–D exchange reactions of gas-phase protonated amino acids with CH3OD

H–D exchange reactions of methanol-d₁ with protonated amino acids were performed in an external-source Fourier transform mass spectrometer. Absolute rate constants were determined for the group which included glycine, alanine, valine, leucine, isoleucine and proline. By comparing reactivities with selected methyl esters, it was found that exchange on the carboxylic acid occurs 3–10 times faster than exchange on the amino group. No simple correlation is observed between the rates of H–D exchange on the acid group and the size of the alkyl group. However, the rates of exchange on the amine decrease with increasing gas-phase basicity. Glycine, the least basic amino acid, exchanges its amine hydrogens the fastest. These results are useful for determining the interaction of methanol with protonated amino acids and can provide insight into the H–D exchange reactions observed with polyprotonated proteins produced by electrospray ionization.     

The gas-phase H/D exchange mechanism of protonated amino acids

A mass spectrometry and Density Functional Theory study of gas-phase H/D exchange in protonated Ala, Cys, Ile, Leu, Met, and Val is reported. Site-specific rate constants were determined and results identify the alpha-amino group as the protonation site. Lack of exchange on the Cys thiol group is explained by the absence of strong intramolecular hydrogen bonding within the reaction complex. In aliphatic amino acids the presence of a methyl group at the beta-C atom was found to lower the site-specific H/D exchange rate for amino hydrogens. Study of the exchange mechanism showed that isotopic exchange occurs in two independent reactions: in one, only the carboxylic hydrogen is exchanged and in the other, both carboxylic and amino group hydrogens exchange. The proposed reaction mechanisms, calculated structures of various species, and a number of structural findings are consistent with experimental data.     

Microwave‐assisted claisen rearrangement. Application to the synthesis of angelicin derivatives

4′‐(Hydroxy, chloro, amino, acetoxy and methoxy)‐methyl‐4,5′‐dimethylangelicins were efficiently and rapidly synthesized via Claisen rearrangement of 4‐methyl‐7‐[4‐(hydroxy, chloro, amino, acetoxy and methoxy)‐but‐2‐ynyloxy]‐coumarins respectively under microwave irradiation. Prominent among the advantages of this new method are operational simplicity, good yields in short reaction times and easy work‐up procedures employed.     

High diastereoselection in the claisen rearrangement of enantiomerically pure butyrolactones

The Claisen rearrangement permits the stereoselective formation of butyrolactone $\text{5b,c}$ or $\text{13b,c}$ through the utilization of enantiomeric lactone $\text{1a}$ and enantiomeric alcohols $\text{2b}$, ent-$\text{2b}$, $\text{2c}$, and ent-$\text{2c}$.     

Palladium(II)-catalyzed claisen rearrangement of allyl vinyl ethers

The Claisen rearrangement of allyl vinyl ethers is catalyzed by PdCl₂(CH₃CN)₂, provided that alkyl substituents protect the vinyl ether double bond from coordination by the metal catalyst.