5,15-Diaryl-beta-substituted-porphyrinato-manganese(III) chlorides as probes for structure-activity relationships in porphyrin-based epoxidation catalysts

Manganese complexes of 5,15-diaryl-beta-substituted-porphyrins were prepared and their behaviour as oxidation catalysts was studied. The role of the pyrrolic and meso-substituents on the activity and selectivity of these catalysts was studied to reveal new structure-activity relationships in these porphyrin-based epoxidation catalysts. The beneficial effect of the halogen atoms at the meso-phenyls is still observed with these catalysts but, for the first time, a strong dependence on the selectivity of the epoxide production was found to be dependent on the nature of the non-halogen substituents at the beta-pyrrolic positions of the porphyrin. Copyright © 2001 John Wiley & Sons, Ltd

New chemistry of diazafulvenium methides: one way to pyrazoles

Diazafulvenium methides generated from the solution pyrolysis of pyrazolo[1,5-c][1,3]thiazole-2,2-dioxides participate in [8[pi]+2[pi]] cycloadditions giving pyrazolo[1,5-a]pyridine derivatives. 1-Methyl-diazafulvenium, generated under flash vacuum pyrolysis reaction conditions, undergoes an intramolecular sigmatropic [1,8]H shift giving 1-vinyl-1H-pyrazoles.http://www.sciencedirect.com/science/article/B6THS-4HR7298-7/1/af0dd8d679e7977f53bc0d4af9a5b68

Synthesis and reactivity of 2-halo-2H-azirines towards nucleophiles

Nucleophilic substitution reactions of 2-halo-2H-azirine with potassium phthalimide and aniline allowed the preparation of new substituted 2H-azirines. The reactions of 2-bromo-3-phenyl-2H-azirine-2-carboxylate with methylamine led to the synthesis of [alpha]-diimines and from the reaction with water, a 3-oxazoline was obtained.http://www.sciencedirect.com/science/article/B6THS-4152YMR-K/1/e94005b66b66b6820ad27458f2562ed

Diels−Alder Reactions of Acyclic 2-Azadienes: A Semiempirical Molecular Orbital Study

Molecular orbital calculations (AM1) have been performed to obtain the frontier orbitals' (HOMO and LUMO) energies and polarization of a series of acyclic 2-azadienes. The results are used to rationalize the reactivity of the compounds studied with both electron-rich and electron-deficient dienophiles as well as the observed regioselectivity of the corresponding Diels−Alder reactions

Synthesis and reactivity of 2-halo-2H-azirines towards nucleophiles

Nucleophilic substitution reactions of 2-halo-2H-azirine with potassium phthalimide and aniline allowed the preparation of new substituted 2H-azirines. The reactions of 2-bromo-3-phenyl-2H-azirine-2-carboxylate with methylamine led to the synthesis of [alpha]-diimines and from the reaction with water, a 3-oxazoline was obtained.http://www.sciencedirect.com/science/article/B6THS-4152YMR-K/1/e94005b66b66b6820ad27458f2562ed

2H-Azirines as dipolarophiles

2H-Azirine-3-carboxylates unsubstituted at C-2 act as dipolarophiles in the reaction with diazomethane giving new 4,5-dihydro-3H-pyrazole derivatives. The synthesis of a pyrimidine was also achieved via 1,3-dipolar cycloaddition of methyl 2-bromo-3-phenyl-2H-azirine-2-carboxylate with an azomethine ylide.http://www.sciencedirect.com/science/article/B6THS-493P1M1-17/1/5df1370edad7138f3cae89fadd9b5c4

Synthesis of 2-halo-2H-azirines from phosphorus ylides

[alpha]-Oxophosphonium ylides (3a-3e) react with N-chlorosuccinimide and N-bromosuccinimide in the presence of azidotrimethylsilane giving the corresponding haloazidoalkenes (4a-4g) with elimination of triphenylphosphine oxide. These compounds were completely converted to the 2H-azirines 5a-5g on heating in heptane.http://www.sciencedirect.com/science/article/B6THS-3VXSK6D-3T/1/9eb19b08a4875f23803d57d6eca5b2d

Synthesis of 2-halo-2H-azirines

[alpha]-Oxophosphonium ylides react with N-chlorosuccinimide, N-bromosuccinimide and N-iodosuccinimide in the presence of azidotrimethylsilane giving the corresponding haloazidoalkenes which were completely converted to the 2-halo-2H-azirines on heating in heptane.http://www.sciencedirect.com/science/article/B6THR-43J0SY1-D/1/db29a4ddcbdab643bfdc11154aaf101

Intramolecular Cycloaddition of Imines of Cysteine Derivatives

Azomethine ylides were generated from Schiffs bases of S-allylcysteine methyl ester and their intramolecular 1,3-dipolar cycloadditions were studied. These reactions led to the synthesis of thieno[3,4-b]pyrrole derivatives in good yiel

Synthesis of novel tricyclic isoindole derivatives

Novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles were prepared from the thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in acetic anhydride. The structure of 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindole 6a was determined by X-ray crystallography.http://www.sciencedirect.com/science/article/B6THS-49PXCD9-X/1/45bd0f04f44115a1e7b644d727569da