Reaction of C-Silylated α-Diazophosphines as Nucleophiles toward Carbonyl Compounds:  A Mechanistic Study and Application to the Synthesis of Alkynes and α-Hydroxyphosphonamides

Abstract

Diversely substituted alpha-hydroxyphosphonamides and alkynes have been efficiently synthesized through the reaction of C-silylated alpha-diazophosphines with different types of aldehydes (2 equiv) in a neutral medium under very mild conditions. The reaction with some chiral aldehydes is highly diastereoselective leading to phosphonamides as single diastereomers. The novel reaction is influenced by electronic and steric effects being precluded for aromatic aldehydes containing electron-releasing substituents on the phenyl ring and for bulky aliphatic aldehydes. The mechanistic studies of these processes, which are highly exothermic, provide evidence for a nucleophilic attack of the diazophosphine to the aldehyde leading to a betaine that rapidly rearranges to a diazomethylenephosphorane, which has been detected or captured in some instances. The diazomethylenephosphorane reacts with a second molecule of aldehyde according to a Wittig-type condensation, and the rate-determining step of the whole process is believed to be the decomposition of the resultant oxaphosphetane to afford the hydroxyphosphonamide and a diazocumulene. Finally, this intermediate loses molecular nitrogen giving a transient carbene that rapidly evolves toward the alkyne.

Reactions of Aldehydes and Ketones and their Derivatives

“…265 ee C-Silylated α-diazophosphines (89, R 1 = Me 2 N or i Pr-N-CH 2 CH 2 -N-i Pr) react with 2 mol of aldehyde under mild neutral conditions to give α-hydroxyphosphonamides (90) and alkynes. 266 Chiral aldehydes can give (90) as single isomers. Isolation of some de intermediates, and labelling studies which show that an aldehydic hydrogen ends up in the alkyne, indicate that the aldehyde is nucleophilically attacked by (89) to give a betaine, which rearranges to a diazomethylenephosphorane, which in turn undergoes a Wittig-type reaction with another molecule of aldehyde.…”

Fullerene Derivatives Incorporating Phosphoramidous Ylide and Phosphoramidate: Synthesis and Property

“…The 1 H NMR spectrum of 4 reveals the presence of a doublet ( J = 27 Hz) at 7.35 ppm that corresponds to an sp 3 -hybridized CH unit directly attached to the fullerene cage; the 31 P NMR spectrum reveals only one signal at 33.86 ppm, which is close to those of common organic alkyl phosphordiamidates (ca. 31−34 ppm) and phosphortriamidates (ca. 24 ppm) .…”