Synthetic approaches to new heterocycles containing two phosphorus atoms

Abstract

Reactions involving nucleophilic attack of tertiary phosphines and related compounds upon acetylenic systems have been reviewed and the literature has been covered to the end of 1970. In an extension of some of the work outlined in the above review, the bisphosphines 1,2- bis (diphenylphosphino)ethane, bis(diphenylphosphino) methane, o'is 1,2-bis (diphenylphosphino)- ethylene and trans 1,2-bis(diphenylphosphino)- ethylene and the biphosphine derivative tetraphenyibiphosphine were treated with the powerful electrophile dimethyl acetylenedicarboxylate in attempts to synthesize new cyclic phosphonium ylides containing two phosphorus atoms. On reaction with the acetylenic ester, the first three of these bisphosphosphines produced in high yield, cyclic phosphonium ylides character ized as dimethyl 1,1,4,4-tetraphenyl-l,4- diphosphacyclohexa-1,3-diene-2,3-dicarboxylate, dimethyl 1,1,3,3-tetraphenyl-5^-l,3-diphosph(V)ole 4,5-dicarboxylate and dimethyl 1,1,4,4-tetraphenyl 1,4-diphosphorin-2,3-dicarboxylate respectively. The adducts were found to be extremely sensitive to water and they were characterized largely by extensive spectroscopic (mainly NMR) investigations although certain cheinical reactions assisted in the structure determinations« Dimethyl 1,1,4,4- tetraphenyl-1,4-diphosphorin-2,3-dicarboxylate showed some evidence of aromatic character. The fourth of the bisphosphines, trans 1,2- bis(diphenyiphosphino)ethylene, was found to react with dimethyl acetylenedicarboxylate to give a 1:1 adduct. NMR evidence suggests that this adduct has a zwitterionic rather than an ylidic structure while protonation experiments, hydrolyses and deuterolyses are consistent with an ylidic structure. The sum of the evidence suggested that the adduct in solution is an equilibrium of two or more isomers in which a zwitterionic form is the major component while an ylidic form is the most reactive component of the mixture. Hydrolysis of the adduct led to an unusual reaction in which one of the diphenyiphosphino groups was eliminated to give a product identical to the 1:1:1 adduct formed from diphenylvinyIphosphine, dimethyl acetylenedicarboxylate and water. A mechanism has been postulated for this reaction and deuterium labelling studies gave some support to this mechanism. Tetraphenylbiphosphine gave a derivative of the o'ls 1,2-bis (diphenylphosphino) ethylene system on reaction with the acetylenic ester.