8 research outputs found
Preparation of Chiral 3-Arylpyrrolidines via the Enantioselective 1,4-Addition of Arylboronic Acids to Fumaric Esters Catalyzed by Rh(I)/Chiral Diene Complexes
A highly efficient rhodium-catalyzed protocol for the preparation of 2-arylsuccinic esters and 3-arylpyrrolidines of high optical purity has been achieved. In the presence of 1 mol % of a chiral diene/Rh(I) catalyst, asymmetric addition of various arylboronic acids to di-<i>tert</i>-butyl fumarate (<b>3c</b>) provides the corresponding adducts in up to 99% yield and 94→99.5% ee. Excellent enantioselectivities were also observed in the regio- and enantioselective conjugate addition of phenylboronic acid (<b>4a</b>) to compound <b>3e</b>
Aerobic Oxidative Coupling of 2‑Naphthol Derivatives Catalyzed by a Hexanuclear Bis(μ-hydroxo)copper(II) Catalyst
A novel hexanuclear bisÂ(μ-hydroxo)ÂcopperÂ(II)
complex, [<b>L</b><sub>3</sub>(Cu<sub>2</sub>(μ-OH)<sub>2</sub>)<sub>3</sub>]Â(ClO<sub>4</sub>)<sub>6</sub> (<b>1</b>), was synthesized
with dinucleating ligand <i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>-tetraÂ(pyridin-2-ylmethyl)-<i>m</i>-xylene diamine (<b>L</b>). Complex <b>1</b> is fully
characterized by X-ray crystallography and magnetic susceptibility
in the solid state and UV–vis and electron paramagnetic resonance
spectroscopy in solution. The molecular structure of <b>1</b> possesses three dicopper cores, in which two copper centers are
bridged by two hydroxide groups and separated by a distance ranging
from 2.8852(15) to 2.8937(10) Ã…. In addition, the three dicopper
cores are linked by the dinucleating ligand between each pair of adjacent
dicopper cores. Importantly, aerobic oxidative coupling of 2,4-di-<i>tert</i>-butylphenol, 2-naphthol, and six 2-naphthol derivatives
was achieved in 33–96% yield using complex <b>1</b> as
a catalyst
Rhodium/Chiral Diene Complexes in the Catalytic Asymmetric Arylation of β‑Pyrazol-1-yl Acrylates
The asymmetric conjugate
addition of arylboronic acids to substituted
and unsubstituted β-pyrazol-1-yl (<i>E</i>)-<i>tert</i>-butyl acrylates <b>4</b> catalyzed by 5 mol %
of the RhÂ(I)/diene <b>2a</b> catalyst provided the corresponding
addition products in 44–98% yield and 91–>99.5% ee.
The method was applied to the formal synthesis of (3<i>S</i>)-3-aryl-3-(pyrazol-1-yl)Âpropanoic acid <b>1b</b> with agonistic
activity toward the human GPR40 G-protein coupled receptor
Rh-Catalyzed Enantioselective Allylation of <i>N</i>‑Tosyl- and <i>N</i>‑Nosylaldimines: Total Synthesis of (−)-Crispine A
The
unprecedented development of asymmetric Rh-catalyzed 1,2-allylation
of <i>N</i>-Ts- and <i>N</i>-Ns-aldimines is achieved.
This protocol utilizes potassium allyltrifluoroborates and various
aldimines to generate enantioenriched homoallylic amines in the presence
of 3.0 mol % of RhÂ(I)/<b>L1b</b> catalyst with up to 90% yield,
98% ee (R = H), and 10:1 diastereoselectivity (R = Me or Ph), yielding
the same major diastereomer when using potassium (<i>E</i>)- and (<i>Z</i>)-crotyltrifluoroborate. Its synthetic
utility is also illustrated in the total synthesis of (−)-crispine
A
Rh(I)-Catalyzed 1,4-Conjugate Addition of Alkenylboronic Acids to a Cyclopentenone Useful for the Synthesis of Prostaglandins
An efficient and <i>trans</i>-diastereoselective RhÂ(I)-catalyzed
1,4-conjugate addition reaction of alkenylboronic acids and a homochiral
(<i>R</i>)-4-silyloxycyclopentenone useful for the synthesis
of derivatives of prostaglandins E and F is described for the first
time. The reaction functions under mild conditions and is particularly
rapid (≤6 h) under low power (50 W) microwave irradiation at
30 °C in MeOH in the presence of a catalytic amount of KOH. Under
these conditions, 3 mol % of [RhClÂ(COD)]<sub>2</sub> is typically
required to produce high yields. The method also functions without
microwave irradiation at 3 °C in the presence of a stoichiometric
amount of KOH. Under these conditions, only 1.5 mol % of [RhClÂ(COD)]<sub>2</sub> is needed, but the reaction is considerably slower. The method
accepts a range of aryl- and alkyl-substituted alkenylboronic acids,
and its utility has been demonstrated by the synthesis of PGF<sub>2α</sub> (dinoprost) and tafluprost
Rhodium-Catalyzed Asymmetric Addition of Arylboronic Acids to β‑Nitroolefins: Formal Synthesis of (<i>S</i>)‑SKF 38393
An efficient enantioselective addition of an array of arylboronic
acids to various β-nitrostyrenes catalyzed by a novel and reactive
rhodium–diene catalyst (S/C up to 1000) was developed, providing
β,β-diarylnitroethanes in good to high yields (62–99%)
with excellent enantioselectivities (85–97% ee). The method
was extended to 2-heteroarylnitroolefins and 2-alkylnitroolefins similarly
providing the desired products with high enantioselectivities and
yields. The usefulness of this method was demonstrated in the formal
synthesis of the enantiomer of the dopamine receptor agonist and antagonist,
SKF 38393
Enantioselective and Rapid Rh-Catalyzed Arylation of <i>N</i>‑Tosyl- and <i>N</i>‑Nosylaldimines in Methanol
Enantiomerically
enriched tosyl-protected diarylmethylamines were
rapidly prepared by the asymmetric addition of arylboronic acids to <i>N</i>-tosylaldimines under mild conditions in the presence of
a catalyst prepared in situ from RhÂ(I) and a chiral diene ligand.
This methodology offers access to diarylmethylamines in good yields
with excellent chiral purity at room temperature using MeOH as a solvent
and NEt<sub>3</sub> as a base. Its synthetic utility was demonstrated
by the preparation of (S)-1-phenyl-1,2,3,4-tetrahydroisoquinoline
(<b>14</b>), an antagonist of the <i>N</i>-methyl-d-aspartate (NMDA) receptor
Enantioselective and Rapid Rh-Catalyzed Arylation of <i>N</i>‑Tosyl- and <i>N</i>‑Nosylaldimines in Methanol
Enantiomerically
enriched tosyl-protected diarylmethylamines were
rapidly prepared by the asymmetric addition of arylboronic acids to <i>N</i>-tosylaldimines under mild conditions in the presence of
a catalyst prepared in situ from RhÂ(I) and a chiral diene ligand.
This methodology offers access to diarylmethylamines in good yields
with excellent chiral purity at room temperature using MeOH as a solvent
and NEt<sub>3</sub> as a base. Its synthetic utility was demonstrated
by the preparation of (S)-1-phenyl-1,2,3,4-tetrahydroisoquinoline
(<b>14</b>), an antagonist of the <i>N</i>-methyl-d-aspartate (NMDA) receptor