Oxidative Cycloamination of Olefins with Aziridines as a Versatile Route to Saturated Nitrogen-Containing Heterocycles

Highly reactive [5,3] and [6,3] bicyclic aziridines can be readily prepared from the corresponding NH aziridines and N-bromosuccinimide by intramolecular oxidative cycloamination of olefins. These compounds, including surprisingly stable exo-methylene bicyclic aziridines, provide versatile synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles

Oxidative Cycloamination of Olefins with Aziridines as a Versatile Route to Saturated Nitrogen-Containing Heterocycles

Highly reactive [5,3] and [6,3] bicyclic aziridines can be readily prepared from the corresponding NH aziridines and N-bromosuccinimide by intramolecular oxidative cycloamination of olefins. These compounds, including surprisingly stable exo-methylene bicyclic aziridines, provide versatile synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles

<i>N</i>-Arylation of Aziridines

A range of N-arylaziridines were prepared by the palladium or copper catalyzed amination reaction between N−H aziridines and aryl bromides or arylboronic acids. These results showcase the synthetic utility of metal-bound aziridine species in nitrogen transfer processes

Strained Enamines as Versatile Intermediates for Stereocontrolled Construction of Nitrogen Heterocycles

This contribution assesses the synthetic utility of molecules that impose conformational constrains onto aziridine-derived enamines. Synthetically versatile [3.1.0] and [4.1.0] bicyclic enamines have been prepared by intramolecular oxidative cycloamination of aziridine-containing olefins. This process is initiated by N-bromosuccinimide followed by base-mediated elimination of HBr to afford highly strained exo-bicyclic enamines. In addition, intramolecular aziridine addition to aldehyde functionality was found to afford the [3.1.0] and [4.1.0] bicyclic hemiaminals. These routes highlight possibilities for chemoselective oxidative transformations of aziridine-containing precursors without nitrogen protection/deprotection steps. The resulting products provide straightforward synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles that are positioned toward subsequent transformations via aziridine ring opening

Strained Enamines as Versatile Intermediates for Stereocontrolled Construction of Nitrogen Heterocycles

This contribution assesses the synthetic utility of molecules that impose conformational constrains onto aziridine-derived enamines. Synthetically versatile [3.1.0] and [4.1.0] bicyclic enamines have been prepared by intramolecular oxidative cycloamination of aziridine-containing olefins. This process is initiated by N-bromosuccinimide followed by base-mediated elimination of HBr to afford highly strained exo-bicyclic enamines. In addition, intramolecular aziridine addition to aldehyde functionality was found to afford the [3.1.0] and [4.1.0] bicyclic hemiaminals. These routes highlight possibilities for chemoselective oxidative transformations of aziridine-containing precursors without nitrogen protection/deprotection steps. The resulting products provide straightforward synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles that are positioned toward subsequent transformations via aziridine ring opening

Strained Enamines as Versatile Intermediates for Stereocontrolled Construction of Nitrogen Heterocycles

This contribution assesses the synthetic utility of molecules that impose conformational constrains onto aziridine-derived enamines. Synthetically versatile [3.1.0] and [4.1.0] bicyclic enamines have been prepared by intramolecular oxidative cycloamination of aziridine-containing olefins. This process is initiated by N-bromosuccinimide followed by base-mediated elimination of HBr to afford highly strained exo-bicyclic enamines. In addition, intramolecular aziridine addition to aldehyde functionality was found to afford the [3.1.0] and [4.1.0] bicyclic hemiaminals. These routes highlight possibilities for chemoselective oxidative transformations of aziridine-containing precursors without nitrogen protection/deprotection steps. The resulting products provide straightforward synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles that are positioned toward subsequent transformations via aziridine ring opening

Synthesis of the Axially Substituted Titanium Pc-C₆₀ Dyad with a Convenient Method

We successfully synthesized the axially substituted titanium Pc-C60 dyad with a convenient method that improves on the traditional asymmetrical phthalocyanine routine to covalently linked phthalocyanines with other functional molecules. The intramolecular photoinduced process between phthalocyanine donor and fullerene acceptor was preliminarily studied

Oligosilane Chain-Length Dependence of Electron Transfer of Zinc Porphyrin−Oligosilane−Fullerene Molecules

A new series of zinc porphyrin−fullerenes bridged by flexible oligosilane chains ZnP−[Sin]−C60 (n = 1−5) was synthesized, and the photophysical properties of these molecules were investigated using steady-state and time-resolved spectroscopic methods. The spectral observations can be well explained by assuming the coexistence of extended conformers and folded conformers, that is, the observed emissions are from the extended conformers while the folded conformers form very short lifetime nonfluorescent excited-state charge-transfer (CT) complexes. Time-resolved transient absorption spectra suggest the generation of intramolecular radical-ion pairs that have sub-microsecond lifetimes. With the number of silicon atoms of the bridged oligosilane, the lifetimes of the radical-ion pairs do not vary regularly, indicating that intramolecular collision of the radical-cation moiety with the radical-anion moiety controls the charge-recombination rate. The attenuation factor of the electron transfer of the silicon chain was evaluated by the bridge-length dependence of charge-separation rate to be 0.16 Å-1 on the basis of the oligosilane chain-length dependence of fluorescence lifetimes. This is the first evaluation of the attenuation factor for the one-dimensional Si−Si chain to the best of our knowledge

Competition between Intramolecular Electron-Transfer and Energy-Transfer Processes in Photoexcited Azulene−C₆₀ Dyad

Photoinduced intramolecular processes in a dyad of azulene and C60 (Az−C60) were compared with those of a dyad of naphthalene and C60 (Naph−C60) on the basis of laser flash photolysis experiments. Upon photoexcitation of C60 in the presence of azulene, intermolecular electron transfer proceeded from azulene to the triplet state of C60 (C60(T1)), although the rate constant was small (107 M-1 s-1), because of the small free-energy change for electron transfer via C60(T1). In Az−C60, it was revealed that the S2 state of the Az moiety (Az(S2)−C60(S0)) donates the excited energy to the C60 moiety, effectively generating Az(S0)−C60(S1). In polar solvents, a charge-separated state (Az•+−C60•-) was generated from Az(S0)−C60(S1), from which the S1 state of the Az moiety (Az(S1)−C60(S0)) was also generated by competitive energy transfer. The lifetimes of the charge-separated states were on the order of nanoseconds. Successive energy-transfer processes {Az(S2)−C60(S0) → Az(S0)−C60(Sn), Az(S0)−C60(S1) → Az(S1) −C60(S0), where n ≥ 2} demonstrate that the multiple energy transfer is achieved in a simple dyad molecule. On the other hand, Naph−C60 dyad did not show charge separation upon excitation of the C60 moiety, but deactivated via intersystem crossing, generating almost quantitatively the C60(T1) moiety. These findings indicate the favorable donor ability of azulene compared to that of naphthalene, even though both azulene and naphthalene have the same 10-π-electron system

Competition between Intramolecular Electron-Transfer and Energy-Transfer Processes in Photoexcited Azulene−C₆₀ Dyad

Photoinduced intramolecular processes in a dyad of azulene and C60 (Az−C60) were compared with those of a dyad of naphthalene and C60 (Naph−C60) on the basis of laser flash photolysis experiments. Upon photoexcitation of C60 in the presence of azulene, intermolecular electron transfer proceeded from azulene to the triplet state of C60 (C60(T1)), although the rate constant was small (107 M-1 s-1), because of the small free-energy change for electron transfer via C60(T1). In Az−C60, it was revealed that the S2 state of the Az moiety (Az(S2)−C60(S0)) donates the excited energy to the C60 moiety, effectively generating Az(S0)−C60(S1). In polar solvents, a charge-separated state (Az•+−C60•-) was generated from Az(S0)−C60(S1), from which the S1 state of the Az moiety (Az(S1)−C60(S0)) was also generated by competitive energy transfer. The lifetimes of the charge-separated states were on the order of nanoseconds. Successive energy-transfer processes {Az(S2)−C60(S0) → Az(S0)−C60(Sn), Az(S0)−C60(S1) → Az(S1) −C60(S0), where n ≥ 2} demonstrate that the multiple energy transfer is achieved in a simple dyad molecule. On the other hand, Naph−C60 dyad did not show charge separation upon excitation of the C60 moiety, but deactivated via intersystem crossing, generating almost quantitatively the C60(T1) moiety. These findings indicate the favorable donor ability of azulene compared to that of naphthalene, even though both azulene and naphthalene have the same 10-π-electron system