A facile synthesis of trisubstituted allenamides by DBU-promoted isomerization of propargylamides

Synthesis of Substituted 1,2-Dihydroisoquinolines by Palladium-Catalyzed Cascade Cyclization–Coupling of Trisubstituted Allenamides With Arylboronic Acids

“…Trisubstituted allenamides for the palladium-catalyzed cascade cyclization were prepared as shown in Scheme 2. The three-component reaction of arylaldehyde, monosubstituted alkyne and obromobenzyl amine gave the propargylamines 1a-1e, which were subjected to the reaction with acetic anhydride and DBU [38], according to our procedure, to afford the corresponding trisubstituted allenamides 2a-2e in moderate to good yields, respectively. The initial attempts for the palladium-catalyzed cascade reaction were carried out using the Nacetyl diphenyl-substituted trisubstituted allenamide 2a with phenylboronic acid (3a) (Table 1).…”

“…Considerable effort has been devoted to developing methods for the synthesis of various N-heterocyclic compounds, but few examples using polysubstituted allenamides have been reported, presumably due to the difficulty in synthesizing polysubstituted allenamides. Recently, we reported a facile synthesis of trisubstituted allenamides via N-acetylation followed by DBU-promoted isomerization, where various substituted allenamides can be conveniently synthesized from readily available propargylamines with high efficiency (Scheme 1, eq 2) [38]. In light of this research background, we focused on the utility of this methodology for the synthesis of substituted 1,2-dihydroisoquinolines.…”

Metal‐Free, Base‐Promoted, Tandem Pericyclic Reaction: A One‐Pot Approach for Cycloheptane‐Annelated Chromones from γ‐Alkynyl‐1,3‐Diketones

“…The structure of 3 a, which contains a seven-membered cycloheptene-fused chromone ring, was confirmed by X-ray crystal analysis. [10] By changing the equivalents of DBU, temperature, and time, the formation of 3 a was still observed but in lower yields (Table 1, entries [9][10][11][12]. Screening of different solvents suggested that DMSO was the most effective solvent for the current protocol (Table 1, entries 13-14).…”

“…When the reaction was conducted in the presence of 10 equivalents of D 2 O, deuterium atoms were incorporated into cyclohepten [b]chromone 3 a-[D1] in four different positions of the seven-membered ring, that is, the alkene (28% and Based on our findings, a plausible reaction mechanism was proposed for the current protocol (Scheme 4). First, the base-mediated keto-enol tautomerism of γ-alkynyl-1,3-diketone generated enolate A, which underwent intramolecular cyclization to produce 3-alkynylchromone intermediate B, [9,12] and subsequent propargyl-allenyl isomerization afforded the 2-methylchromone allene intermediate D. [9,12c] Allene D was postulated to undergo a 1,5-hydride shift to produce the triene intermediate E, [13] which upon the isomerization afforded the conjugated triene intermediate F.…”

Synthesis of Substituted 1,2-Dihydroisoquinolines by Palladium-Catalyzed Cascade Cyclization–Coupling of Trisubstituted Allenamides with Arylboronic Acids

“…Recently, we reported a facile synthesis of trisubstituted allenamides via N -acetylation followed by DBU-promoted isomerization, where various substituted allenamides were conveniently synthesized from readily available propargylamines with high efficiency ( Scheme 1 , eq. 2) [ 38 ]. In light of this research background, we focused on the utility of this methodology for the synthesis of substituted 1,2-dihydroisoquinolines via the palladium-catalyzed cascade cyclization of ortho-haloaryl-substituted allenamides with arylboronic acids.…”