10 research outputs found
DMAP Promoted Tandem Addition Reactions Forming Substituted Tetrahydroxanthones
Substituted
tetrahydroxanthones are constructed using a DMAP-promoted
tandem nucleophilic addition process. The reaction yields range from
39% to 73%. Disubstituted tetrahydroxanthones are generated as a ∼2.3:1
mixture of diastereomers favoring the formation of the <i>trans</i>-isomer
DMAP Promoted Tandem Addition Reactions Forming Substituted Tetrahydroxanthones
Substituted
tetrahydroxanthones are constructed using a DMAP-promoted
tandem nucleophilic addition process. The reaction yields range from
39% to 73%. Disubstituted tetrahydroxanthones are generated as a ∼2.3:1
mixture of diastereomers favoring the formation of the <i>trans</i>-isomer
Total Synthesis of Cladoniamide G
The total synthesis of cladoniamide G, a cytotoxic compound against MCF-7 breast cancer cells (10 μg/mL), was accomplished. Key steps in the sequence include oxidative dimerization of 3-acetoxy-5-chloroindole and a tandem process incorporating three steps: bimolecular carbonyl addition, lactam formation, and carbamate removal
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Annulated Isoxazoles via [3 + 2] Cycloaddition of Alkenyl Bromides and Oximoyl Chlorides and Ag(I) Promoted Elimination
Substituted
salicylaldehydes are converted to fused tetracyclic
isoxazoles through a synthetic sequence incorporating substitution
of 2-bromo-2-cyclohexen-1-ol, formation of an oxime function, conversion
to an oximoyl chloride, intramolecular [3 + 2] cycloaddition, and
elimination of an equivalent of hydrogen bromide using silverÂ(I) carbonate.
Six examples of this sequence are presented
Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands
The synthesis of enantiomerically
pure pyridine-bridged phosphaalkene-oxazolines
ArPî—»CÂ(Ph)Â(2,6-C<sub>5</sub>H<sub>3</sub>NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCHÂ(<i>i</i>-Pr)ÂCH<sub>2</sub>/ÂCNOCHÂ(CH<sub>2</sub>Ph)ÂCH<sub>2</sub>) is reported.
This new ligand forms a κÂ(P), κ<sup>2</sup>(NN) dimeric
complex with copperÂ(I) (<b>7</b>) that dissociates into a cationic
κ<sup>3</sup>(PNN) monomeric complex upon addition of a neutral
ligand {[<b>1a</b>·CuL]ÂOTf (<b>8a</b>–<b>e</b>): L = PPh<sub>3</sub> (<b>a</b>), PÂ(OPh)<sub>3</sub> (<b>b</b>), 2,6-lutidine (<b>c</b>), 4-DMAP (<b>d</b>), 1-methylimidazole (<b>e</b>)}. The P–Cu bond lengths
in <b>8</b> are influenced by the π-accepting/σ-donating
properties of L, and this can be observed by changes in the δ<sup>31</sup>P<sub>PC</sub> NMR shift. The donor–acceptor
properties in complexes of type <b>8</b> have also been investigated
by UV/vis spectroscopy and density functional theory calculations
Reaction of an Enantiomerically Pure Phosphaalkene-Oxazoline with MeM Nucleophiles (M = Li and MgBr): Stereoselectivity and Noninnocence of the P‑Mesityl Substituent
The addition of alkyl
nucleophiles (MeM, M = Li, MgBr) across the
Pî—»C bond of an enantiomerically pure phosphaalkene-oxazoline
followed by protonation of the C anion affords phosphines with three
chirality centers. The formation of palladiumÂ(II) complexes of the
resultant phosphines permitted structural characterization of the
products by X-ray diffraction. The choice of nucleophile has a profound
effect on the product distributions. For instance, the Grignard reagent
adds in a diastereoselective manner to give one major phosphine product
with P- and C-stereocenters. In contrast, addition of methyllithium
has proven not only to be less stereoselective but also affords a
fascinating cyclic phosphine product. Both the Grignard and RLi reactions
involve proton transfer from the <i>o</i>-Me of the P-Mes
substituent even though the products are quite different in each case
Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands
The synthesis of enantiomerically
pure pyridine-bridged phosphaalkene-oxazolines
ArPî—»CÂ(Ph)Â(2,6-C<sub>5</sub>H<sub>3</sub>NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCHÂ(<i>i</i>-Pr)ÂCH<sub>2</sub>/ÂCNOCHÂ(CH<sub>2</sub>Ph)ÂCH<sub>2</sub>) is reported.
This new ligand forms a κÂ(P), κ<sup>2</sup>(NN) dimeric
complex with copperÂ(I) (<b>7</b>) that dissociates into a cationic
κ<sup>3</sup>(PNN) monomeric complex upon addition of a neutral
ligand {[<b>1a</b>·CuL]ÂOTf (<b>8a</b>–<b>e</b>): L = PPh<sub>3</sub> (<b>a</b>), PÂ(OPh)<sub>3</sub> (<b>b</b>), 2,6-lutidine (<b>c</b>), 4-DMAP (<b>d</b>), 1-methylimidazole (<b>e</b>)}. The P–Cu bond lengths
in <b>8</b> are influenced by the π-accepting/σ-donating
properties of L, and this can be observed by changes in the δ<sup>31</sup>P<sub>PC</sub> NMR shift. The donor–acceptor
properties in complexes of type <b>8</b> have also been investigated
by UV/vis spectroscopy and density functional theory calculations