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, ArPC­(Ph)­(3-C₆H₄Ox) [<b>1a</b>,<b>b</b>, Ar = Mes (<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCH­(^<i>i</i>Pr)­CH₂], are reported. The radical-initiated homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional poly­(methylene­phosphine) (<b>4a</b>: <i>M</i>_n = 5300 g mol^–1, PDI = 1.2) and poly­(methylene­phosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i>_n = 4000 g mol^–1, 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–P­(CHPhAr) (i.e., S–<b>1a</b>) and ArCH₂–CH₂ (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 ¹³C­{¹H} 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 Au­(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i>_n = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i>_n = 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, ArPC­(Ph)­(3-C₆H₄Ox) [<b>1a</b>,<b>b</b>, Ar = Mes (<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCH­(^<i>i</i>Pr)­CH₂], are reported. The radical-initiated homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional poly­(methylene­phosphine) (<b>4a</b>: <i>M</i>_n = 5300 g mol^–1, PDI = 1.2) and poly­(methylene­phosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i>_n = 4000 g mol^–1, 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–P­(CHPhAr) (i.e., S–<b>1a</b>) and ArCH₂–CH₂ (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 ¹³C­{¹H} 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 Au­(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i>_n = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i>_n = 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, ArPC­(Ph)­(3-C₆H₄Ox) [<b>1a</b>,<b>b</b>, Ar = Mes (<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCH­(^<i>i</i>Pr)­CH₂], are reported. The radical-initiated homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional poly­(methylene­phosphine) (<b>4a</b>: <i>M</i>_n = 5300 g mol^–1, PDI = 1.2) and poly­(methylene­phosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i>_n = 4000 g mol^–1, 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–P­(CHPhAr) (i.e., S–<b>1a</b>) and ArCH₂–CH₂ (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 ¹³C­{¹H} 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 Au­(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i>_n = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i>_n = 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 silver­(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 ArPC­(Ph)­(2,6-C₅H₃NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCH­(<i>i</i>-Pr)­CH₂/­CNOCH­(CH₂Ph)­CH₂) is reported. This new ligand forms a κ­(P), κ²(NN) dimeric complex with copper­(I) (<b>7</b>) that dissociates into a cationic κ³(PNN) monomeric complex upon addition of a neutral ligand {[<b>1a</b>·CuL]­OTf (<b>8a</b>–<b>e</b>): L = PPh₃ (<b>a</b>), P­(OPh)₃ (<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 δ³¹P_PC 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 PC bond of an enantiomerically pure phosphaalkene-oxazoline followed by protonation of the C anion affords phosphines with three chirality centers. The formation of palladium­(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 ArPC­(Ph)­(2,6-C₅H₃NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCH­(<i>i</i>-Pr)­CH₂/­CNOCH­(CH₂Ph)­CH₂) is reported. This new ligand forms a κ­(P), κ²(NN) dimeric complex with copper­(I) (<b>7</b>) that dissociates into a cationic κ³(PNN) monomeric complex upon addition of a neutral ligand {[<b>1a</b>·CuL]­OTf (<b>8a</b>–<b>e</b>): L = PPh₃ (<b>a</b>), P­(OPh)₃ (<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 δ³¹P_PC 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