Abstract
Triphenylphosphine reacts with dialkyl acetylenedicarboxylates in the presence of methyl carbamate to generate stable phosphorus ylides. These ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. Quantum mechanical calculations were employed to check the stability of the two geometrical isomers. To determine the kinetic parameters and mechanistic investigation of the reactions, they were monitored by UV spectrophotometry. Useful information was obtained from studies of the effect of solvent, the structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants, on the rate of reactions. The proposed mechanism was confirmed according to the obtained experimental results, and a steady state approximation. The first ( k2) and third ( k3) steps of the reactions were recognized as the ratedetermining and fast steps, respectively, on the basis of experimental data.
Highlights
In recent years there has been increasing interest in the synthesis of organophosphorus compounds.1-14 A large number of methods have appeared describing novel syntheses of organophosphorus compounds.1,2 There are many studies on the reaction between trivalent phosphorus nucleophiles and α, β-unsaturated carbonyl compounds in the presence of a proton source such as an alcohol or phenol.5As part of our current studies on the development of new routes to stable phosphorus ylides,11-14 we describe the reaction between triphenylphosphine 1 and dialkyl acetylenedicarboxylates 2 in the presence of methyl carbamate 3 which leads to the corresponding stable phosphorus ylids 4 in fairly high yield
The ylide moiety of these compounds is strongly conjugated with the adjacent carbonyl group and rotation around the partial double bond in (E)-4(a,b) and (Z)-4(a,b) geometrical isomers is slow on the NMR time-scale at ambient temperature (Scheme 1)
On the basis of the well-established chemistry of trivalent phosphorus nucleophiles,3-7 it is reasonable to assume that phosphorus ylide 4 results from the initial addition of triphenylphosphine to the acetylenic esters and subsequent protonation of the 1:1 adduct by the methyl carbamate to form phosphoranes 4
Summary
In recent years there has been increasing interest in the synthesis of organophosphorus compounds. A large number of methods have appeared describing novel syntheses of organophosphorus compounds. There are many studies on the reaction between trivalent. As part of our current studies on the development of new routes to stable phosphorus ylides, we describe the reaction between triphenylphosphine 1 and dialkyl acetylenedicarboxylates 2 in the presence of methyl carbamate 3 which leads to the corresponding stable phosphorus ylids 4 in fairly high yield. These ylides usually exist as a mixture of the two geometrical isomers, some are only found as one isomer. Assignment of the relative stability of the (Z)- and E-isomers is possible in phosphorus ylides by experimental methods such as 1H, 13C NMR and IR spectroscopy and mass spectrometry. Quantum mechanical calculations have been performed for comparison with the experimental data in order to gain a better understanding of the most important geometrical parameters and relative energies of the (Z)- and E-geometrical isomers
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
