1,738,182 research outputs found
Desymmetrization of 1,4-Dien-3-ols and Related Compounds via Ueno−Stork Radical Cyclizations
No full textDesymmetrization of 1,4-dien-3-ols and related compounds via Ueno−Stork radical cyclizations is reported. The stereochemistry of the cyclization
is controlled by the acetal center. Excellent stereocontrol at C(4) and C(5) of the newly formed tetrahydrofuran rings is observed. Use of a
chiral auxiliary allows the preparation of enantiomerically pure material. The utility of this method has been demonstrated by achieving a short
synthesis of (+)-eldanolide, the pheromone of the male African sugarcane stem borer Eldana saccharina
New and Efficient Catalytic Route to Bicyclo[3.3.0]octa-1,5-dien-3-ones
No full textThe silylcarbobicyclization of 4,4-disubstituted 1,6-heptadiynes
with tert-butyldimethylsilane catalyzed by Rh(acac)(CO)2,
Co2Rh2(CO)12, or
(t-BuNC)4RhCo(CO)4 under
50 atm of
carbon monoxide gives the corresponding novel 7,7-disubstituted
2-silylbicyclo[3.3.0]octa-1,5-dien-3-ones in good yields. A possible mechanism is proposed.
The unique feature of
this strained skeleton is discussed on the basis of 13C NMR
and X-ray crystallographic
analyses
Rh(I)-Catalyzed Intramolecular Allenic Pauson−Khand Reaction: Construction of a Bicyclo[5.3.0]dec-1,7-dien-9-one Skeleton
No full text1-Phenylsulfonylallenes possessing a hexynyl appendage in refluxing toluene in the presence of catalytic amount of rhodium(I) catalyst under
a carbon monoxide atmosphere underwent regioselective formal [2 + 2 + 1]-cycloaddition to produce the corresponding bicyclo[5.3.0]dec-1,7-dien-9-one derivatives in acceptable yields
Economic Analysis and Environment Impact Assessment of Water-based Economic Activities in Tam Giang - Cau Hai Lagoon, Thua Thien Hue Province
No full textOxidative Fragmentation of Pregna-14,16-dien-20-ones to 14β-Hydroxyandrost-15-en-17-ones
No full textTwo methods have been developed for efficient conversion of pregna-14,16-dien-20-ones into 14β-hydroxyandrost-15-en-17-ones. One procedure consists of treatment of the ring-D dienone successively with sodium borohydride and singlet oxygen. The reaction is illustrated by the conversion of
pregna-14,16-dien-20-one 1 into 14β-hydroxyandrost-15-en-17-one 3, via the corresponding allylic
alcohol 2. Although this two-step procedure is simple, it provides 3 in relatively low yield,
accompanied by a smaller amount of the isomeric 14α-hydroxyandrost-15-en-17-one 6. An alternative
one-step conversion is achieved by treatment of dienone 1 with a peroxyacid in the presence of a
strong protic acid. This process is illustrated by the two-step conversion of dienone 1 into hydroxy
ketone 11 in 51% overall yield (Scheme 5) and by the analogous conversion of dienone 13 into
hydroxy ketone 24 in 61% overall yield (Scheme 11)
Radical Ion Probes. 8. Direct and Indirect Electrochemistry of 5,7-Di-<i>tert</i>-butylspiro[2.5]octa-4,7-dien-6-one and Derivatives
No full textResults pertaining to the direct and indirect electrochemistry of
5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1a),
1-methyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one
(1b), and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1c) are
reported. Product analyses reveal that reduction of all these
substrates
leads to cyclopropane ring-opened products; ring opening occurs with
modest selectivity leading to the more
substituted (stable) distonic radical anion. The direct
electrochemistry of these compounds is characterized
by rate limiting electron transfer (with α ≈ 0.5), suggesting that
while ring opening is extremely rapid, the
radical anions do have a discrete lifetime (i.e., electron
transfer and ring opening are not concerted).
Utilizing
homogeneous redox catalysis, rate constants for electron transfer
between 1a, 1b, and 1c and a series of
aromatic
radical anions were measured; reduction potentials and reorganization
energies were derived from these rate
constants by using Marcus theory
Ecdysteroid 7,9(11)-dien-6-ones as potential photoaffinity labels for ecdysteroid binding proteins
No full textThree ecdysteroid 7,9(11)-dien-7-ones (dacryhainansterone, 25-hydroxydacryhainansterone and kaladasterone) were prepared by dehydration of the corresponding 11a-hydroxy ecdysteroids (ajugasterone C, turkesterone and muristerone A, respectively). The biological activities of the dienones in the Drosophila melanogaster B(II) cell bioassay, which reflect the affinity for the ecdysteroid receptor complex, showed that the dienones retain high biological activity. Irradiation at 350 nm of the ecdysteroid dienones (100 nM) with bacterially-expressed dipteran and lepidopteran ecdysteroid receptor proteins (DmEcR/DmUSP or CfEcR/CfUSP), followed by loading with [(3)H]ponasterone A revealed that irradiation of dacryhainansterone or kaladasterone resulted in blocking of >70% of the specific binding sites. Thus, ecdysteroid dienones show considerable potential as photoaffinity analogues for ecdysteroid binding proteins
Atlas céleste, comprenant toutes les cartes de l'ancien atlas de Ch. Dien, rectifié, augmenté et enrichi de cartes nouvelles... par Camille Flammarion. 3 e édition - Paris : Gauthier-Villars, 1877 : Nébuleuse. Uranographe, Charles Dien Camille Flammarion (1842-1925)
No full textTextes imprimés et illustrésCet atlas, publié initialement par Charles Dien en 1851, revu et augmenté par Camille Flammarion, propose une cartographie du ciel qui recense plus de 100 000 étoiles et nébuleuses. Il est admirablement illustré de planches lithographiques en couleurs qui invitent à la rêverie et font le succès populaire de ce type d'ouvrage scientifique.téléchargeabl
Reinvestigation of Mycothiazole Reveals the Penta-2,4-dien-1-ol Residue Imparts Picomolar Potency and 8<i>S</i> Configuration
No full textReinvestigation of mycothiazole (1) revealed picomolar
potency (IC50 = 0.00016, 0.00027, 0.00035 μM) against
pancreatic, (PANC-1), liver (HepG2), and colon (HCT-116) tumor cell
lines. Reevaluation of 1 provided [α]D data indicating Vanuatu specimens of C. mycofijiensis contain the 8S enantiomer of 1 and
not the 8R configuration previously reported. Semisynthesis
provided 8-O-acetylmycothiazole (2),
8-oxomycothiazole (8), mycothiazole nitrosobenzene derivatives
(MND1, MND2: 9a, 9b), and MND3 (10) with IC50 = 0.00129, >1.0, >1.0, >1.0, >1.0
μM,
respectively, against PANC-1 cell lines. These results highlight the
significance of the penta-2,4-dien-1-ol residue as a key structural
feature of 1 required for its cytotoxicty against tumor
cell lines
Cascade Radical 1,6-Addition/Cyclization of <i>para</i>-Quinone Methides: Leading to Spiro[4.5]deca-6,9-dien-8-ones
No full textA cascade
three-component iodoazidation of para-quinone methides
to construct spiro[4.5]deca-6,9-dien-8-ones under
mild conditions has been developed. The chemoselective 1,6-addition
of azide radical triggered a regioselective 5-exo-dig cyclization/radical
coupling sequence, enabling C–N, C–C, and C–I
bond formations in a one-pot procedure with high efficiency
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