5 research outputs found
Hydration of Terminal Alkynes Catalyzed by Water-Soluble Cobalt Porphyrin Complexes
Water-soluble cobaltÂ(III) porphyrin complexes were found
to promote
the hydration of terminal alkynes to give methyl ketones. The alkyne
hydration proceeded in good to excellent yield with 0.1 to 2 mol %
cobalt catalyst <b>1</b> and was compatible with the presence
of acid/base- or redox-sensitive functional groups such as alkyl silyl
ethers; allyl ethers; trityl ethers; benzyl ethers; carboxylic esters;
boronic esters; carboxamides; nitriles; and nitro, iodo, and acetal
groups. Some of the alkyne substrates tested here are otherwise difficult
to hydrate. The alkyne hydration can be performed on a gram scale,
and the catalyst can be recovered by aqueous workup
Hydration of Terminal Alkynes Catalyzed by Water-Soluble Cobalt Porphyrin Complexes
Water-soluble cobaltÂ(III) porphyrin complexes were found
to promote
the hydration of terminal alkynes to give methyl ketones. The alkyne
hydration proceeded in good to excellent yield with 0.1 to 2 mol %
cobalt catalyst <b>1</b> and was compatible with the presence
of acid/base- or redox-sensitive functional groups such as alkyl silyl
ethers; allyl ethers; trityl ethers; benzyl ethers; carboxylic esters;
boronic esters; carboxamides; nitriles; and nitro, iodo, and acetal
groups. Some of the alkyne substrates tested here are otherwise difficult
to hydrate. The alkyne hydration can be performed on a gram scale,
and the catalyst can be recovered by aqueous workup
Structural and Mechanistic Insights into the C–C Bond-Forming Rearrangement Reaction Catalyzed by Heterodimeric Hinokiresinol Synthase
Hinokiresinol synthase (HRS) from Asparagus
officinalis consists of two subunits, α
and β, and catalyzes an unusual decarboxylative rearrangement
reaction of 4-coumaryl 4-coumarate to generate (Z)-hinokiresinol with complete stereoselectivity. Herein, we describe
the mechanism of rearrangement catalysis and the role played by the
heterodimeric HRS, through structural and computational analyses.
Our results suggest that the HRS reaction is unlikely to proceed via
the previously hypothesized Claisen rearrangement mechanism. Instead,
we propose that the 4-coumaryl 4-coumarate substrate is first cleaved
into coumarate and an extended p-quinone methide,
which then recombine to generate a new C–C bond. These processes
are facilitated by proton transfers mediated by the basic residues
(α-Lys164, α-Arg169, β-Lys168, and β-Arg173)
in the cavity at the heterodimer interface. The active site residues,
α-Asp165, β-Asp169, β-Trp17, β-Met136, and
β-Ala171, play crucial roles in controlling the regioselectivity
of the coupling between the fragmented intermediates as well as the
stereoselectivity of the decarboxylation step, leading to the formation
of the (Z)-hinokiresinol product
Substrate Conformation Correlates with the Outcome of Hyoscyamine 6β-Hydroxylase Catalyzed Oxidation Reactions
Hyoscyamine 6β-hydroxylase
(H6H) is an α-ketoglutarate
dependent mononuclear nonheme iron enzyme that catalyzes C6-hydroxylation
of hyoscyamine and oxidative cyclization of the resulting product
to give the oxirane natural product scopolamine. Herein, the chemistry
of H6H is investigated using hyoscyamine derivatives with modifications
at the C6 or C7 position as well as substrate analogues possessing
a 9-azabicyclo[3.3.1]Ânonane core. Results indicate that hydroxyl rebound
is unlikely to take place during the cyclization reaction and that
the hydroxylase versus oxidative cyclase activity of H6H is correlated
with the presence of an <i>exo</i>-hydroxy group having <i>syn</i>-periplanar geometry with respect to the adjacent H atom
to be abstracted
N‑Methylation of Amines with Methanol at Room Temperature
N-Methylation
of amines with methanol proceeds at room temperature
in the presence of a silver-loaded titanium dioxide (Ag/TiO<sub>2</sub>) photocatalyst under UV–vis light irradiation. This method
allows facile synthesis/isolation of <i>N</i>-methylamines
bearing various functional groups including <i>N</i>-benzyl, <i>N</i>-allyl, <i>N</i>-Boc, hydroxyl, ether, acetal,
carboxamide, formamide, and olefin groups