Synthesis and reactivity of 3-(dialkylamino)allenyl phosphonium salts. PPh3-mediated synthesis of pyrroles from propyne iminium triflates

Abstract

The ambident cations of propyne iminium trifluoromethanesulfonates (triflates) 1 react with triphenyl-or tributylphosphane exclusively in a conjugate addition to form highly moisturesensitive [3-(dialkylamino)allenyl]phosphonium triflates 2 and 4. Allene 2f, bearing a methyl group at the enamine α-position, rearranges to form (3-morpholinobuta-1,3-dienyl)phosphonium salt 3 under the reaction conditions. The rather electron-rich allenes are easily protonated by triflic acid to form dicationic 3-phosphonio-prop-2-ene iminium bis(triflates) 5, one of which (5a) was characterized by X-ray crystal structure determination. Hydrolysis of the allenes yields (3-oxoprop-1-enyl)phosphonium triflates 6 (-+ PPh 3 ) or 8 (-+ PBu 3 ). Salts 6 can also be prepared by simultaneous addition of PPh 3 and triflic acid to acetylenic ketones. Salts 2 are converted thermally into 1,2,3,5-tetrasubstituted pyrroles 10; this reaction can be used for a PPh 3 -mediated conversion of propyne iminium salts 1 into pyrroles 10 without isolation of the allenylphosphonium salt intermediate.

Synthesis of a Stable Iminium Salt and Propellane Derivatives

“…Among them, compound 7b with a 17- i -Bu group was isolated as a crystalline product and its structure was determined by X-ray crystallography. To the best of our knowledge, examples of X-ray crystallography of iminium ions are very rare except for the case of conjugated iminium ions . An example most resembling the desired iminiums 3 and 7 is Fe(CO) 3 complex of iminium tetrafluoroborate 8 (Figure ). , In the case of the iminium 8 , anchimeric participation of the double bond derived from a homoallylic system and an inert counteranion, tetrafluoroborate would stabilize the iminium ion.…”

DFT mechanistic investigation of the 1,2‐reduction of α,β‐unsaturated ynones

“…Thus, the oxo forms (6-E and 6-Z) were anticipated to be more stable, which was supported by the calculated energy difference between the two structures (ΔG Z-oxo-enol = 21.8 kcal mol À 1 , ΔE Z-oxo-enol = 21.1 kcal mol À 1 ). These structures (6) were previously isolated in the presence of triflic acid, [29], [30], [38] which demonstrates the high stability of this system.…”

From 1-Sulfonyl-4-aryl-1,2,3-triazoles to 1-Allenyl-5-aryl-1,2,3-triazoles

“…By surfing the literature, alkynes and enynes might hitherto be the most popular starting materials in the preparation of allenes. For instance, the archaic isomerism of alkyne in the presence of base, S N 2′ nucleophilic substitution on propargylic electrophiles, Pd-catalyzed coupling reactions of propagylic acetates/halides with organometallic reagents, allenylation of terminal alkyne (ATA) reactions, 1,4-addition or 1,6-addition to enynes. , The subject of this work regioselectively provided 1-allenyl-5-aryl-1,2,3-triazoles, using tosyl as directing group.…”