30 research outputs found
PREPARATION OF 5H,7H-DIBENZ[c,e]OXEPIN-5-ONE DERIVATIVE THROUGH RECONSTRUCTION OF THE LACTONE RING
The systematic investigation of the efficient transformation of 6H-dibenzo[b,d]pyran-6-one into 5H,7H-dibenz[c,e]oxepin-5-one is described
SYNTHESIS OF ZANTHOXYLINE AND ITS RELATED COMPOUNDS: REVISION OF THE REPORTED STRUCTURE
Benzo[c]phenanthridine alkaloid, zanthoxyline, was synthesized through an intramolecular biaryl coupling reaction of N-naphthylbenzamide derivative using a palladium reagent. Comparison of the NMR data for the synthetic product with that reported previously revealed that the proposed structure was incorrect. Synthesis of the related compounds suggested that the correct structure of zanthoxyline is the previously known decarine
Syntheses of All-Methylated Ellagitannin, Isorugosin B and Rugosin B
Ellagitannins possess a wide range of biological activities and remarkable structural diversity, which commonly include an axially chiral biaryl unit. This paper describes syntheses of all-methylated versions of isorugosin B and rugosin B, which are regioisomeric, ellagitannin-related compounds. The key features of these syntheses involve the construction of an axially chiral biaryl function on a sugar moiety through a Pd-catalyzed intramolecular biaryl coupling reaction, Bringmann’s atroposelective lactone opening reaction, and a two-step ester formation. This is the first synthetic approach for generating ellagitannins featuring a valoneoyl group
SYNTHESIS OF 2,3,9,10-TETRAOXYGENATED BENZO[c]PHENANTHRIDINE DERIVATIVES VIA PALLADIUM-MEDIATED ARYL-ARYL COUPLING REACTION
Two 2,3,9,10-tetraoxygenated benzo[c]phenanthridine alkaloids, 1 2, originally reported as zanthoxyline and broussonpapyrine, respectively, were synthesized using the Pd-mediated intramolecular aryl-aryl coupling reaction as the key step
REGIOSELECTIVITY OF THE INTRAMOLECULAR BIARYL COUPLING REACTION OF 3-SUBSTITUTED PHENYL 2-IODOBENZOATE USING A PALLADIUM REAGENT
This study investigated the regioselectivity of the intramolecular coupling reaction of the phenyl benzoate derivative which possesses a methyl or methoxy group at the meta-position of the phenoxy moiety. The type of base and the presence/absence of the phosphine ligand influenced the product ratio. A transition state model and the regioselectivity of the reaction are discussed
Synthesis of graphislactones A-D through a palladium-mediated biaryl coupling
The chemical synthesis of graphislactones A-D was achieved through the Pd-mediated intramolecular biaryl coupling reaction of phenyl benzoate derivatives.</p
SYNTHESIS OF NIGRICANIN VIA INTRAMOLECULAR BIARYL COUPLING REACTION OF FUNCTIONALIZED PHENYL BENZOATE
A tetracyclic natural product, nigricanin (1), was synthesized through an intramolecular biaryl coupling reaction of the phenyl benzoate derivative which was derived from the corresponding phenol and benzoic acid
Enantioselective construction of biaryl part in the synthesis of stegane related compounds
A Pd-mediated intramolecular aryl-aryl coupling reaction of phenyl benzoate derivatives were examined to form benzo[c]chromen-6-ones, and then enantioselective lactone-opening reaction with a borane-oxazaborolidine combination was carried out. The resulting biphenyl was transformed into a key intermediate for the stegane related compounds. The absolute configuration of the biphenyl is also discussed.
Stegane and related compounds are important because of their interesting biological activities such as antileukemic properties.1 One of the most outstanding features of their chemical structures is an unsymmetrical 2,2’-disubstituted biphenyl moiety with an axial chirality (Figure 1). For the formation of such a biphenyl part in the syntheses of the stegane families, several approaches have been attempted such as photocyclization,2 Suzuki coupling,3 oxidative biaryl coupling,4 the SNAr reaction,5 Ullmann coupling,6 and the [2+2+2] three-component cyclization reaction.7</p
Lyman Alpha Emitters at z=7 in the Subaru/XMM-Newton Deep Survey Field: Photometric Candidates and Luminosity Function
We conducted a deep narrowband NB973 (FWHM = 200 A centered at 9755 A) survey
of z=7 Lyman alpha emitters (LAEs) in the Subaru/XMM-Newton Deep Survey Field,
using the fully depleted CCDs newly installed on the Subaru Telescope
Suprime-Cam, which is twice more sensitive to z=7 Lyman alpha at ~ 1 micron
than the previous CCDs. Reaching the depth 0.5 magnitude deeper than our
previous survey in the Subaru Deep Field that led to the discovery of a z=6.96
LAE, we detected three probable z=7 LAE candidates. Even if all the candidates
are real, the Lyman alpha luminosity function (LF) at z=7 shows a significant
deficit from the LF at z=5.7 determined by previous surveys. The LAE number and
Lyman alpha luminosity densities at z=7 is ~ 7.7-54% and ~5.5-39% of those at
z=5.7 to the Lyman alpha line luminosity limit of L(Ly-alpha) >~ 9.2 x 10^{42}
erg s^{-1}. This could be due to evolution of the LAE population at these
epochs as a recent galaxy evolution model predicts that the LAE modestly
evolves from z=5.7 to 7. However, even after correcting for this effect of
galaxy evolution on the decrease in LAE number density, the z=7 Lyman alpha LF
still shows a deficit from z=5.7 LF. This might reflect the attenuation of
Lyman alpha emission by neutral hydrogen remaining at the epoch of reionization
and suggests that reionization of the universe might not be complete yet at
z=7. If we attribute the density deficit to reionization, the intergalactic
medium (IGM) transmission for Lyman alpha photons at z=7 would be 0.4 <=
T_{Ly-alpha}^{IGM} <= 1, supporting the possible higher neutral fraction at the
earlier epochs at z > 6 suggested by the previous surveys of z=5.7-7 LAEs, z ~
6 quasars and z > 6 gamma-ray bursts.Comment: Accepted to ApJ for publicatio
The RMS Survey: Critical Tests of Accretion Models for the Formation of Massive Stars
There is currently no accepted theoretical framework for the formation of the
most massive stars, and the manner in which protostars continue to accrete and
grow in mass beyond \sim10Msun is still a controversial topic. In this study we
use several prescriptions of stellar accretion and a description of the
Galactic gas distribution to simulate the luminosities and spatial distribution
of massive protostellar population of the Galaxy. We then compare the
observables of each simulation to the results of the Red MSX Source (RMS)
survey, a recently compiled database of massive young stellar objects. We find
that the observations are best matched by accretion rates which increase as the
protostar grows in mass, such as those predicted by the turbulent core and
competitive accretion (i.e. Bondi-Hoyle) models. These 'accelerating accretion'
models provide very good qualitative and quantitative fits to the data, though
we are unable to distinguish between these two models on our simulations alone.
We rule out models with accretion rates which are constant with time, and those
which are initially very high and which fall away with time, as these produce
results which are quantitatively and/or qualitatively incompatible with the
observations. To simultaneously match the low- and high-luminosity YSO
distribution we require the inclusion of a 'swollen-star' pre-main-sequence
phase, the length of which is well-described by the Kelvin-Helmholz timescale.
Our results suggest that the lifetime of the YSO phase is \sim 10^5yrs, whereas
the compact Hii-region phase lasts between \sim 2 - 4 \times 10^5yrs depending
on the final mass of the star. Finally, the absolute numbers of YSOs are best
matched by a globally averaged star-formation rate for the Galaxy of
1.5-2Msun/yr.Comment: 22 pages, 24 figures. Accepted for publication in MNRA