3-{5-Bromo-2-[(tri-phenyl-phosphanyl-idene)amino]-phen-yl}-4,5-di-hydro-1,2,3-oxa-diazol-3-ylium-5-olate.

In general, sydnone compounds are synthesized with an aromatic substituent at the N-3 position and this feature adds to the stability of the mesoionic five-membered heterocyclic ring. In the title compound, C26H19BrN3O2P, the aromatic substitutent is tri-phenyl-phosphine 4-bromo-phenyl-imide. The dihedral angle between the planes of the sydnone and the attached phenyl ring is 45.98 (7)°. In the crystal, the mol-ecules packed as pairs in which the sydnone rings lie in parallel planes separated by 0.849 Šand sandwiched between two parallel phenyl rings. The mol-ecules inter-act through cyclic C-H⋯O=C hydrogen bonds.

4-Acetyl-3-[2-(eth-oxy-carbon-yl)phen-yl]sydnone.

Sydnones, which contain a mesoionic five-membered heterocyclic ring, are more stable if synthesized with an aromatic substutuent at the N3 position. In the title compound {sys-tematic name: 4-acetyl-3-[2-(eth-oxy-carbon-yl)phen-yl]-1,2,3-oxa-diazol-3-ylium-5-olate}, C13H12N2O5, the aromatic substitutent is 2-(eth-oxy-carbon-yl)phenyl. Intra- and inter-molecular hydrogen bonds are observed. The inter-planar angle between the sydnone and benzene rings is 71.94 (8)°. π-ring⋯carbon-yl inter-actions of 3.2038 (16) Šarise between the sydnone ring and a symmetry-related C=O group.

3-(2-Acetamido-phen-yl)sydnone.

Sydnones are unusual mesoionic compounds containing a five-membered heterocyclic ring. Generally for stability, substitution at the N-3 position by an aromatic fragment is necessary. In the title compound, C(10)H(9)N(3)O(3), the aromatic substitutent is 2-acetamido-phenyl. The two planar ring fragments are twisted relative to one another, with a inter-planar angle of 63.13 (5)°. The mol-ecules are packed into the unit cell via π-π inter-actions between the phenyl rings [inter-planar separation = 3.4182 (4) Å] and between the sydnone rings [inter-planar separation = 3.2095 (4) Å]. N-H⋯O and C-H⋯O hydrogen bonding is also found inter-nally and externally to the mol-ecule.

Improved alkylation and product stability in phosphotriester formation through quinone methide reactions with dialkyl phosphates.

Investigating reactions of functionalized p-quinone methides continues to advance our design of a reagent being developed for controlled, in situ modification of DNA via phosphodiester alkylation. Previously reported investigations of p-quinone methides derived from catechols allowed for trapping of isolable trialkyl phosphates for characterization and mechanistic information. However, lactone formation with these derivatives required long reaction times, resulting in an unfavorable mixture of trialkyl phosphate and hydrolysis products. To enhance the rate and efficacy of trialkyl phosphate formation and trapping, a phenol derived p-quinone methide has been designed to enforce a conformation favoring lactonization of the dialkyl phosphate alkylated intermediate. The relative rates of phosphodiester alkylation and subsequent trapping of the phosphotriester adduct have been examined by UV and (1)H NMR analysis for p-quinone methide precursor 1 and the corresponding control, 1'. The incorporation of a methyl group at the meta-position of 1 (relative to 1') significantly improves the rate of lactionization to provide a much higher yield of the desired product, lactonized phosphotriester 5. The control reaction with 1' afforded only a minor amount of the corresponding lactonized trialkyl phosphate 5'.

Structure-optical property relationships in organometallic sydnones.

As part of an effort to develop a spectroscopic structure-property relationship in platinum acetylide oligomers, we have prepared a series of mesoionic bidentate Pt(PBu3)2L2 compounds containing sydnone groups. The ligand is the series o-Syd-(C6H4-C[triple bond]C)n-H, where n = 1-3, designated as Syd-PEn-H. The terminal oligomer unit consists of a sydnone group ortho to the acetylene carbon. We synthesized the platinum complex (Syd-PEn-Pt), the unmodified ligands (PEn-H), and the unmodified platinum complexes (PEn-Pt). The compounds were characterized by various methods, including X-ray diffraction, 13C NMR, ground-state absorption, fluorescence, phosphorescence, and laser flash photolysis. From solving the structure of Syd-PE1-Pt, we find the angle between the sydnone group and the phenyl group is 45 degrees . By comparison of the 13C NMR spectra of the sydnone-containing ligands, the sydnone complexes with the corresponding unmodified ligands and complexes not containing the sydnone group, the sydnone group is shown to polarize the nearest acetylenes and have a charge-transfer interaction with the platinum center. Ground-state absorption spectra of the complexes in various solvents give evidence that the Syd-PE1-Pt complex has an excited state less polar than the ground state, while the PE1-Pt complex has an excited state more polar than the ground state. In all the higher complexes the excited state is more polar than the ground state. The phosphorescence spectrum of the Syd-PE1-Pt complex has an intense vibronic progression distinctly different from the PE1-Pt complex. The sydnone effect is small in Syd-PE2-Pt and negligible in Syd-PE3-Pt. From absorption and emission spectra, we measured the singlet-state energy E(S), the triplet-state energy E(T), and the singlet-triplet splitting Delta E(ST). By comparison with energies obtained from the unmodified complexes, attachment of the sydnone lowers E(S) by approximately 0.1 eV and raises E(T) by approximately 0.1 eV. As a result, the sydnone group lowers Delta E(ST) by approximately 0.2 eV. The trends suggest one of the triplet-state singly occupied molecular orbitals (SOMOs) is localized on the sydnone group, while the other SOMO resides on the rest of the ligand.

Phosphodiester Alkylation with a Quinone Methide.

Despite the wide array of studies involving DNA alkylation and cleavage with quinone methide generating compounds, there have been no reports on the alkylation of phosphodiesters with quinone methides. We have investigated the reaction of dialkyl phosphates with a p-quinone methide in order to determine the potential for alkylation to produce trialkyphosphates. These studies have revealed that a phosphodiester can be alkylated with a p-quinone methide when promoted by a Brønsted acid. The role of the Brønsted acid is to sufficiently activate the p-quinone methide to allow phosphodiester addition to occur. The alkyl substituents of the phosphodiester have been found to effect the reactivity of the dialkyl phosphate under the reaction conditions examined. Equilibrium conversions up to 83% trialkyl phosphate formation have been achieved.