Study on the Reactions of Acetylenic Aldehydes with Dimethyl Phosphite in Basic Media: Phosphonate‐Phosphate Rearrangement versus 5‐exo‐dig Cyclization Reactions

Abstract

Tandem reactions of various acetylenic aldehydes with dimethyl phosphite in basic media were investigated. It was shown that in the case of a non-activated triple bond of the starting materials, the well-known Pudovik reaction followed by a subsequent phosphonate-phosphate rearrangement took place. On the other hand when the triple bond of the starting materials is activated by electron-withdrawing heterocycles, a smooth and regioselective tandem 5-exo-dig cyclization reactions becomes possible.

Palladium‐catalysed O‐Allylation of α‐Hydroxyphosphonates: An Expedient Entry into Phosphono‐oxaheterocycles

“…In the light of their biological potential, it is not surprising that numerous synthetic routes have been explored for the formation of these phosphono derivatives. Besides methods involving substitution at C1 of a pyranose or a furanose with a phosphite in the presence of a Lewis acid (Scheme , A), various studies have explored the cyclization of α‐hydroxyphosphonate intermediates via either a substitution reaction or the addition on an alkene, an alkyne, or a carbonyl moiety (Scheme , B)…”

Gold-Catalyzed Access to 1H-Isochromenes: Reaction Development and Mechanistic Insight

“…However, as stated before, the regioselectivity of the process is highly dependent on the medium; the different factors responsible for the mechanism and outcome of the reaction are the following: i Basicity: the base promotes deprotonation of the nucleophile (e.g., methanol) enhancing the attack on the aldehyde to form an hemiacetal anion that facilitates the 5- exo-dig attack on the alkyne (Scheme ). Now, the domino process has been reversed to a nucleophilic addition/cyclization transformation. ii Nature of the metal: a given transition metal in high oxidation state (hard nature, oxophilic) tends to activate the carbonyl moiety rather than that in lower oxidation state (soft nature, carbophilic), which will coordinate to the C–C triple bond (Scheme ). , iii Substituents (R and R′): the electronic effect of both groups conditions the electrophilicity of each carbon atom in the alkyne (Scheme ).…”

“…Basicity: the base promotes deprotonation of the nucleophile (e.g., methanol) enhancing the attack on the aldehyde to form an hemiacetal anion that facilitates the 5- exo-dig attack on the alkyne (Scheme ). Now, the domino process has been reversed to a nucleophilic addition/cyclization transformation.…”

Lanthanide Silylamide-Catalyzed Synthesis of Pyrano[2,3-b]indol-2-ones

“…First, diethyl phosphite goes through a rapid deprotonation initiated by the lanthanide silylamide, generating catalytically active species A . The central lanthanide ion of A then coordinates to the ketone carbonyl moiety of the isatin, and a Pudovik reaction occurs to form intermediate B , which undergoes rapid [1,2]-phospha-Brook rearrangement to generate intermediate C . As the key intermediate of the cycle, C abstracts the proton of the diethyl phosphite to produce phosphate 5a and regenerate active species A to accomplish the first catalytic cycle.…”