Conformational Preference in 1,3-Dithianes Containing 2-Phosphoryl, -(thiophosphoryl), and -(selenophosphoryl) groups. Chemical and Crystallographic Implications of the Nature of the Anomeric Effect
摘要:
The operation of the anomeric effect in all the title compounds studied was found. The magnitude of the anomeric effect was found to be larger than 10 kJ/mol. Crystallographic, spectroscopic, and thermodynamic data suggest that the n(S)-sigma*(C-P) hyperconjugative interaction is one of the factors responsible for the anomeric effect. The second interaction stabilizing the axial position of phosphorus can be P=Y...H(4 or 6) hydrogen bond formation. Some other interactions are also possible, namely sigma(C(4,6)-S)-sigma*(C(2)-P) (preferring the equatorial position of phosphorus) and sigma(C(4,6)-S)-pi(P=Y) hyperconjugations and the n(S)-n(Y) repulsions. The latter interaction was also proposed as MO counterpart of lone pair-lone pair repulsions suggested by molecular mechanics calculations. It was proved that various conformation probes can afford different equilibrium constants, if weighted average method and conformationally fixed models are applied. Most of the physical quantities are dependent on the alkyl substitution in the 1,3-dithiane ring. Thus, the relevant procedure for the selection of conformational probe was presented. Since the gamma-effect value in C-13 NMR spectra was found to be very sensitive to the position of a substituent connected with the anomeric carbon atom of 1,3-dithianes, it was applied as a conformational probe. A long range (4)J(C-P) coupling constant in the C-13 NMR spectra and P-31 spin-lattice T-1(DD) relaxation times suggest the existence of close contact(s) between a heteroatom Y(Y=O,S,Se) connected with the axial phosphorus P=Y and axial protons H(4,6) in the 1,3-dithiane ring. Crystallographic data show that the distance from Y to one of these protons is usually much smaller than to the other one and smaller than the sum of H,Y van der Waals radii. The possibility of H..Y hydrogen bond formation is discussed.
The thermal- and photo-reactions of a diphenylphosphinite ester with 10-methylacridinium iodide. Discrimination between polar and single electron transfer processes.
摘要:
The thermal-reaction of isopropyl diphenylphosphinite with 10-methylacridinuim iodide results in the formation of a phosphonium ion through a polar process, whereas the reaction under the irradiation of light affords 10-methylacridan as well as isopropyl diphenylphosphinate through single electron transfer (SET) from the former to the latter.
Efficient Method for the Preparation of Carboxylic Acid Alkyl Esters or Alkyl Phenyl Ethers by a New-Type of Oxidation–Reduction Condensation Using 2,6-Dimethyl-1,4-benzoquinone and Alkoxydiphenylphosphines
A new-type of oxidation–reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1...
Water determines the products: an unexpected Brønsted acid-catalyzed PO–R cleavage of P(<scp>iii</scp>) esters selectively producing P(O)–H and P(O)–R compounds
作者:Chunya Li、Qi Wang、Jian-Qiu Zhang、Jingjing Ye、Ju Xie、Qing Xu、Li-Biao Han
DOI:10.1039/c9gc01254k
日期:——
selectivity of Brønsted acid-catalyzed C–O cleavage reactions of trialkylphosphites: with water, the reaction quickly takes place at room temperature to afford quantitative yields of H-phosphonates; without water, the reaction selectively affords alkylphosphonates in high yields, providing a novel halide-free alternative to the famous Michaelis–Arbuzov reaction. This method is general as it can be readily
Efficient Methods for the Preparation of Alkyl−Aryl and Symmetrical or Unsymmetrical Dialkyl Ethers between Alcohols and Phenols or Two Alcohols by Oxidation−Reduction Condensation
作者:Taichi Shintou、Teruaki Mukaiyama
DOI:10.1021/ja0487877
日期:2004.6.1
generated in situ from chlorodiphenylphosphine (2) and alcohols, 2,6-dimethyl-1,4-benzoquinone (3), and phenols proceeds smoothly to afford alkyl-aryl ethers in good to high yields under neutral conditions. In a similar fashion, a new and efficient method for the preparation of symmetrical or unsymmetrical dialkyl ethers in good to high yields is established via tetrafluoro-1,4-benzoquinone (fluoranil) (4)
Various alkyl phenyl ethers were obtained in high yields by way of oxidation-reduction condensation where alkoxydiphenylphosphine, prepared easily from chlorodiphenylphosphine and corresponding alcohols, was treated with various phenols in the co-existence of 2,6-dimethyl-1,4-benzoquinone(DMBQ) under mild conditions.