18 research outputs found
Synthesis of Functionalized Cyclohexenone Core of Welwitindolinones via Rhodium-Catalyzed [5 + 1] Cycloaddition
The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5 + 1]-cycloaddition of an allenylcyclopropane with CO. A pentasubstituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates
Stereoselective Total Synthesis of Hainanolidol and Harringtonolide via Oxidopyrylium-Based [5 + 2] Cycloaddition
The
tetracyclic carbon skeleton of hainanolidol and harringtonolide
was efficiently constructed by an intramolecular oxidopyrylium-based
[5 + 2] cycloaddition. An anionic ring-opening strategy was developed
for the cleavage of the ether bridge in 8-oxabicyclo[3.2.1]颅octenes
derived from the [5 + 2] cycloaddition. Conversion of cycloheptadiene
to tropone was realized by a sequential [4 + 2] cycloaddition, Kornblum鈥揇eLaMare
rearrangement, and double elimination. The biomimetic synthesis of
harringtonolide from hainanolidol was also confirmed
Rhodium-Catalyzed Tandem Annulation and (5 + 1) Cycloaddition: 3鈥慔ydroxy-1,4-enyne as the 5鈥慍arbon Component
A Rh-catalyzed
tandem annulation and (5 + 1) cycloaddition was
realized. 3-Hydroxy-1,4-enyne served as the new 5-carbon component
for the (5 + 1) cycloaddition.
Substituted carbazoles, dibenzofurans, and tricyclic compounds containing
a cyclohexadienone moiety could be prepared efficiently. The identification
of a byproduct suggests that metal carbene and ketene intermediates
may be involved in the (5 + 1) cycloaddition
Harnessing the Reactivity of Iridium Hydrides by Air: Iridium-Catalyzed Oxidation of Aldehydes to Acids in Water
An
iridium-catalyzed oxidation of aldehydes to acids was realized
by using air as the oxidant and water as the solvent in the presence
of base. Interestingly, the same type of catalysts were also used
for the reduction of aldehydes under acidic conditions. A common iridium
hydride intermediate is proposed for both redox reactions. The oxidation
has a number of advantages such as high yields, great functionality
tolerance, and easy purification without chromatography
Rhodium-Catalyzed Carbonylation of 3-Acyloxy-1,4-enynes for the Synthesis of Cyclopentenones
Functionalized cyclopentenones were synthesized by a Rh-catalyzed carbonylation of 3-acyloxy-1,4-enynes, derived from alkynes and 伪,尾-unsaturated aldehydes. The reaction involved a Saucy鈥揗arbet 1,3-acyloxy migration of propargyl esters and a [4 + 1] cycloaddition of the resulting acyloxy substituted vinylallene with CO
Syntheses, structures, and properties of two 2-D Cd(II) complexes based on 2-(1<i>H</i>-imidazol-1-methyl)-1<i>H</i>-benzimidazole and polycarboxylate ligands
<div><p>Two 2-D Cd(II) complexes, {[Cd(imb)(bdc)(H<sub>2</sub>O)]路CH<sub>3</sub>OH}<sub><i>n</i></sub> (<b>1</b>) and {[Cd(imb)(Hbtc)(CH<sub>3</sub>OH)]路2H<sub>2</sub>O路CH<sub>3</sub>OH}<sub><i>n</i></sub> (<b>2</b>), have been synthesized by reactions of CdCl<sub>2</sub>路2.5H<sub>2</sub>O with 2-(1<i>H</i>-imidazol-1-methyl)-1<i>H</i>-benzimidazole (imb) and 1,3-benzenedicarboxylic acid (H<sub>2</sub>bdc) or 1,3,5-benzenetricarboxylic acid (H<sub>3</sub>btc). Single-crystal X-ray diffraction shows that <b>1</b> possesses an infinite 2-D layered structure in which all the carboxylates chelate Cd(II) and imb bridge Cd(II) ions. Complex <b>2</b> also features an infinite 2-D layered structure and imb ligands also bridge Cd(II) ions, but two carboxylates of each 1,3,5-benzenetricarboxylate coordinate to Cd(II) in monodentate or chelating mode, leaving the third one, which is not deprotonated, uncoordinated. IR spectra, fluorescent properties, and thermogravimetric analyses of both complexes have been investigated.</p></div
Rh-Catalyzed (5+2) Cycloadditions of 3鈥慉cyloxy-1,4-enynes and Alkynes: Computational Study of Mechanism, Reactivity, and Regioselectivity
The mechanism of Rh-catalyzed (5+2)
cycloadditions of 3-acyloxy-1,4-enyne
(ACE) and alkynes is investigated using density functional theory
calculations. The catalytic cycle involves 1,2-acyloxy migration,
alkyne insertion, and reductive elimination to form the cycloheptatriene
product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes
(VCPs), in which alkyne inserts into a rhodium鈥揳llyl bond,
alkyne insertion into a Rh鈥揅颅(sp<sup>2</sup>) bond is preferred.
The 1,2-acyloxy migration is found to be the rate-determining step
of the catalytic cycle. The electron-rich <i>p</i>-dimethylaminobenzoate
substrate promotes 1,2-acyloxy migration and significantly increases
the reactivity. In the regioselectivity-determining alkyne insertion
step, the alkyne substituent prefers to be distal to the forming C鈥揅
bond and thus distal to the OAc group in the product
Chiral Catalyst-Directed Dynamic Kinetic Diastereoselective Acylation of Lactols for <i>De Novo</i> Synthesis of Carbohydrate
The
control of the stereochemistry at the anomeric position is
still one of the major challenges of synthetic carbohydrate chemistry.
We have developed a new strategy consisting of a chiral catalyst-directed
acylation followed by a palladium-catalyzed glycosidation to achieve
high 伪- and 尾-stereoselectivity on the anomeric position.
The former process involves a dynamic kinetic diastereoselective acylation
of lactols derived from Achmatowicz rearrangement, while the latter
is a stereospecific palladium-catalyzed allylic alkylation
Rhodium-Catalyzed Carbonylation of Cyclopropyl Substituted Propargyl Esters: A Tandem 1,3-Acyloxy Migration [5 + 1] Cycloaddition
We have developed two different types of tandem reactions
for the
synthesis of highly functionalized cyclohexenones from cyclopropyl
substituted propargyl esters. Both reactions were initiated by rhodium-catalyzed
Saucy鈥揗arbet 1,3-acyloxy migration. The resulting cyclopropyl
substituted allenes derived from acyloxy migration then underwent
[5 + 1] cycloaddition with CO. The acyloxy group not only eased the
access to allene intermediates but also provided a handle for further
selective functionalizations
Rhodium-Catalyzed Chemo- and Regioselective Cross-Dimerization of Two Terminal Alkynes
Cross-dimerization of terminal arylacetylenes and terminal propargylic alcohols/amides has been achieved in the presence of a rhodium catalyst. This method features high chemo- and regioselectivities rendering convenient and atom economical access to functionalized enynes