Conformational Analysis of (2-Substituted-alkyl)phosphoryl Compounds. 1. NMR Spectroscopic Studies of Dialkyl (2-Hydroxyalkyl)phosphonates and Their Carboxylic Esters
作者:Daniel G. Genov、John C. Tebby
DOI:10.1021/jo950364n
日期:1996.1.1
Twelve (2-substituted-alkyl)phosphonates (2, 3) were synthesized and conformational analyses carried out by NMR spectroscopy. The conformational populations in six solvents with different polarities and in the presence of metal ions (Li+, Na+, Zn2+), were studied. Steric effects were studied by variation of the sizes of alkyl groups R(1) and R(2) and intramolecular interactions studied by derivatization of the hydroxy group X. In (2-hydroxyalkyl)phosphonates the most stable conformer ga, in which the phosphoryl group is gauche to the hydroxy group and anti to the alkyl group (R(1)), is favored particularly in less polar solvents such as C6D6 and CDCl3. In polar solvents the population of the less stable conformer ag, in which the phosphoryl group is gauche to the alkyl group (R(1)) and anti to the hydroxy group, is increased. Smaller alkyl groups R(1) (Me, Pr-n) allow more conformational freedom. Conversion of the hydroxy group to its carboxylic ester reduces the population of conformer ga so that, for R(1) = Pr-n, conformers go and ag are approximately equally populated. The presence of metal salts in the acetone-d(6) solutions causes an increase in the population of conformer ga in both (2-hydroxyalkyl)phosphonates and their carboxylic ester derivatives. The chemical shift difference between the diastereotopic alpha-methylene protons has been shown to be proportional to the population of conformer ga.
Kinetic resolution of 2-hydroxy-2-aryl-ethylphosphonates by a non-enzymatic acylation catalyst
作者:Laura Mesas-Sánchez、Alba E. Díaz-Álvarez、Petr Koukal、Peter Dinér
DOI:10.1016/j.tet.2014.03.102
日期:2014.6
Optically pure hydroxyphosphonates are widely used as derivatizable compounds that can be incorporated into a variety of synthetic strategies for the preparation of other high value organic products. A non-enzymatic kinetic resolution procedure to obtain chiral 2-hydroxy-2-arylethylphosphonates from the easily available racemic counterparts is described. A range of 2-hydroxy-2-arylethylphosphonates was efficiently resolved employing a planar-chiral DMAP derived catalyst with good selectivities (up to S=68). The chiral hydroxyphosphonates were isolated in good yields and high enantiomeric excess (>94% ee). (C) 2014 Elsevier Ltd. All rights reserved.
The Olefin Synthesis from<i>β</i>-Hydroxyalkylphosphonates Induced by Fluorides or Relatively Weak Bases
β-Hydroxyalkylphosphonates, which were prepared readily from alkylphosphonates and carbonyl compounds, were treated with a fluoride ion such as CsF or with relatively weak bases such as K2CO3 in N,N-dimethylformamide to give the corresponding olefins in good yields. One molar equivalent of water to bases is effective for increasing the yields of olefins. The stereochemistry of erythro-dimethyl (2-hydroxy-1-methyl-2-phenyl)ethylphosphonate was determined by X-ray crystallographic analysis. Use of threo-isomer gave (E)-olefin exclusively, while that of erythro-enriched isomer afforded predominantly (Z)-olefin, indicating that the present olefination proceeds stereospecifically in a manner of syn-elimination.
Kinetic resolution of beta-hydroxyalkanephosphonates was efficiently performed by 2-fluorobenzoylation in the presence of copper(II) triflate and (R,R)-Ph-BOX as a catalyst with good s value of up to 21 (C) 2010 Elsevier Ltd. All rights reserved.