14 research outputs found
An optimized divergent synthesis of sulfonimide-based dendrimers achieving the fifth generation
3-R-4-Nitro-6,7-furoxanobenzo[d]isoxazoles – a new type of condensed nitroarenes capable of Diels–Alder reaction
Triaryl-Substituted Divinyl Ketones Cyclization: Nazarov Reaction versus Friedel–Crafts Electrophilic Substitution
The acid-catalyzed cyclization
of a wide range of triaryl-substituted divinyl ketones has been studied.
It was found that the reaction pathway strongly depends on the nature
of the aryl substituent at the α-position to the carbonyl group.
An electron-rich aromatic substituent promotes the reaction to proceed
through the intramolecular Friedel–Crafts electrophilic substitution
giving dihydronaphthalene derivatives. In contrast, the presence
of an electron-deficient substituent is favorable for the Nazarov
4π-conrotatory cyclization yielding triaryl-substituted cyclopentenones.
The electrophilic substitution reaction was applied to thiophene and
thiazole derivatives
Aerobic Dimerization of Ethyl 4‑Thienyl-3-ketobutanoate toward a Modifiable Photochromic Diarylethene Precursor
A unique chemical
transformation, the base-induced aerobic dimerization
of ethyl 4-(2,5-dimethylthiophen-3-yl)-3-ketobutanoate leading to
photochromic diarylethene with a 4-hydroxy-4-methylcyclopent-2-ene-1-one
as an ethene bridge, is described. This compound is easily subjected
to various chemical modifications and can be used as a new diarylethene
precursor to produce photoactive compounds with desired properties
and functions
General Photoinduced Sequential Electrocyclization/[1,9]-Sigmatropic Rearrangement/Ring-Opening Reaction of Diarylethenes
A novel
and efficient photochemical transformation of diarylethenes
comprising a five-membered heterocyclic ring and phenyl moiety is
described. This reaction provides a simple method for the preparation
of functionalized naphthalene derivatives via photorearrangement reaction
of diarylethenes, and the process is characterized by high efficiency
that was determined by NMR monitoring. Some mechanistic aspects of
this process have been also explored. It was found that the reaction
includes tandem transformation of three basic processes: the photocyclization
of the hexatriene system, [1,9]-sigmatropic rearrangement, and heterocyclic
ring opening. Diarylethenes with different heterocycle moieties (thiophene,
benzo[<i>b</i>]thiophene, furan, indole, imidazole, thiazole,
oxazole, pyrazole) have been involved into this process, and the target
naphthalenes with good yields have been obtained. The opportunity
for use in the transformation of diarylethenes with different heterocyclic
residues permits synthesis of naphthalenes with desired functional
groups. The general character and high efficiency of the reaction
promise that the transformation can be an effective synthetic route
for the annulation of benzene rings to various aromatic systems, including
heterocycles
Triaryl-Substituted Divinyl Ketones Cyclization: Nazarov Reaction versus Friedel–Crafts Electrophilic Substitution
The acid-catalyzed cyclization
of a wide range of triaryl-substituted divinyl ketones has been studied.
It was found that the reaction pathway strongly depends on the nature
of the aryl substituent at the α-position to the carbonyl group.
An electron-rich aromatic substituent promotes the reaction to proceed
through the intramolecular Friedel–Crafts electrophilic substitution
giving dihydronaphthalene derivatives. In contrast, the presence
of an electron-deficient substituent is favorable for the Nazarov
4π-conrotatory cyclization yielding triaryl-substituted cyclopentenones.
The electrophilic substitution reaction was applied to thiophene and
thiazole derivatives
Structural and Spectral Properties of Photochromic Diarylethenes: Size Effect of the Ethene Bridge
The
effect of the size of the ethene bridge on the structural and
spectral properties of photochromic diarylethenes, which remains a
poorly understood phenomenon, was studied as applied to diarylethenes
containing unsymmetrical (cyclohexenone and cyclopentenone) and symmetrical
(cyclohexene and cyclopentene) ethene bridges. Thiophene, oxazole,
and imidazole derivatives were used as aryl moieties. An increase
in the size of the ethene bridge in the cycloalkenone series was found
to be accompanied by a hypsochromic shift of the absorption maximum
of the photoinduced form, whereas no difference was found for cycloalkenes.
A detailed analysis of the NMR spectra (including 2D experiments)
revealed previously unknown effects associated with the existence
of an intramolecular hydrogen bond (CH···N) between
the six-membered ethene bridge and the azole substituents. The NMR
experimental data obtained were confirmed by DFT quantum chemical
calculations and X-ray analysis. It was found that an intramolecular
hydrogen bond favors an increase of the quantum yield of the photocyclization
reaction
Photoinduced Skeletal Rearrangement of Diarylethenes Comprising Oxazole and Phenyl Rings
A novel
photochemical rearrangement of diarylethenes bearing oxazole
and benzene derivatives as aryl moieties that results in the formation
of polyaromatic systems was investigated. The mechanism of the transformation
includes photocyclization, sequential [1,9] and [1,3]-hydrogen shifts,
as well as a lateral oxazole ring-opening process. It was shown that
this reaction can be an effective synthetically preparative method
for the preparation of naphthalene (polyaromatic) derivatives
Nitro-imidazoles in ferrocenyl alkylation reaction. Synthesis, enantiomeric resolution and in vitro and in vivo bioeffects
Ferrocenylalkyl nitro-imidazoles (4a-h, 5a-h) were prepared via the regiospecific reaction of the α-(hydroxy)alkyl ferrocenes, FcCHR (OH) (1a–h; Fc = ferrocenyl; R = H, Me, Et, Pr, i-Pr, Ph, ortho-Cl-Ph, ortho-I-Ph), with nitro-imidazoles in aqueous organic medium (H2O-CH2Cl2) at room temperature in the presence of HBF4, within several minutes in good yields. X-ray structural data for racemic (R,S)-1-N-(benzyl ferrocenyl)-2-methyl-4-nitroimidazole (5f) were determined. The resulting enantiomers were resolved into enantiomers by analytical HPLC on modified amylose or cellulose chiral stationary phases. The viabilities of 4b, 4d, 5b, 5c in vitro, and in experiments in vivo antitumor effects of 1-N-ferrocenylethyl-4-nitroimidazole (4b) against murine solid tumor system Ca755 carcinoma were evaluated
Regio- and Chemoselective Bromination of 2,3-Diarylcyclopent-2-en-1-ones
The bromination of 2,3-diarylcyclopent-2-en-1-ones under
various
conditions has been studied. It was found that depending on the brominating
reagent and nature of solvent the bromine atom can be introduced at
the 4- or 5-position of the ethene “bridge”, as well
as into the aryl moieties. Aryl group bromination is accomplished
with such reagents as molecular bromine, <i>N</i>-bromosuccinimide,
or tetrabutylammonium tribromide. 5-Bromocyclopentenones with very
high efficiency can be obtained by the reaction with copper(II) bromide
in methanol, while 4-bromoketones are prepared in <i>n</i>-propyl acetate. The developed methods can be highly useful for the
synthesis of bromo-substituted 2-cyclopenten-1-ones and their close
analogues, which are important synthons in organic synthesis and for
the preparation of a variety of useful substances