1,2-Dihydroisoquinolines as Templates for Cascade Reactions To Access Isoquinoline Alkaloid Frameworks

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

1,2-Dihydroisoquinolines are important compounds due to their biological and medicinal activities, and numerous approaches to their synthesis have been reported. 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. In light of this research background, we focused on the utility of this methodology for the synthesis of substituted 1,2-dihydroisoquinolines. In this study, a palladium-catalyzed cascade cyclization-coupling of trisubstituted allenamides containing a bromoaryl moiety with arylboronic acids is described. When N-acetyl diphenyl-substituted trisubstituted allenamide and phenylboronic acid were treated with 10 mol% of Pd(OAc)2, 20 mol% of P(o-tolyl)3, and 5 equivalents of NaOH in dioxane/H2O (4/1) at 80 °C, the reaction proceeded to afford a substituted 1,2-dihydroisoquinoline. The reaction proceeded via intramolecular cyclization, followed by transmetallation with the arylboronic acid of the resulting allylpalladium intermediate. A variety of highly substituted 1,2-dihydroisoquinolines were concisely obtained using this methodology because the allenamides, as reaction substrates, were prepared from readily available propargylamines in one step.

Synthesis of substituted 1,2-dihydroisoquinolines via Ni(ii) and Cu(i)/Ag(i) catalyzed double nucleophilic addition of arylamines to ortho-alkynyl donor-acceptor cyclopropanes (o-ADACs)

A concise approach for the synthesis of substituted 1,2-dihydroisoquinolines via double nucleophilic addition of primary arylamines to ortho-alkynyl donor-acceptor cyclopropanes (o-ADACs) in the presence of a catalytic Ni(ClO₄)₂·6H₂O and CuI/AgOTf system has been developed. Further applying this protocol, some of the derived malonates were converted into the corresponding monoesters under Krapcho decarboxylation reaction conditions. Thereafter, these esters were transformed into the respective acids and alcohols. In addition, multifunctionalized 4-(2,2,2-trifluoroacetyl) 1,2-dihydroisoquinolines were also obtained with excess TFAA.

Dual function of carbon tetrachloride: synthesis of chlorinated heterocycles

An efficient tandem approach to invent highly chlorinated and structurally diversified dihydropyridine fused heterocycles from easily accessible ortho-alkynylaldehydes and primary amines under metal-free conditions via four sequential bond formations is described. The proposed tandem route proceeds via a carbon tetrachloride-mediated 6-endo-dig ring closure followed by nucleophilic attack of the trichloromethyl anion.

Carbon Tetrachloride-Mediated Cyclization of (2-Alkynyl)arylaldimines for the Synthesis of Polychlorinated Nitrogen Heterocycles

An unprecedented use of carbon tetrachloride to mediate the 6-endo-dig cyclization of (2-alkynyl)arylaldimines, generated in situ from (2-alkynyl)arylaldehydes and primary amines, has been developed via formal insertion of C═N and C≡C bonds into a C-Cl bond under catalyst-free conditions, providing convenient access to a range of structurally diverse polychlorinated 1,2-dihydroisoquinolines and heteroarene-fused nitrogen heterocycles.

An expedient approach to 1,2-dihydroisoquinoline derivatives via cobalt catalysed 6-endo dig cyclization followed by Mannich condensation of o-alkynylarylaldimines

A highly effective 6-endo dig cyclisation of o-alkynylaldimines to 1,2-dihydroisoquinolines has been described via direct and nitro Mannich condensation using inexpensive and readily available cobalt chloride as catalyst. This strategy provides an effective procedure for the synthesis of substituted 1,2-dihydroisoquinolines derivatives in moderate to high yields. An addition of pronucleophiles, such as nitromethane, acetone and α-hydroxyacetone, to o-alkynylarylaldimines has been achieved via isoquinolinium intermediate.

Silver-catalyzed reaction of enynals with alkenes: a tandem 1,3-dipolar cycloaddition/cyclopropanation

A silver-catalyzed reaction of enynals with alkenes to synthesize a series of polycyclic compounds has been developed. The reaction occurred smoothly using enynals with electron-deficient alkynes or terminal alkynes as substrates. The reaction was proposed to proceed through a tandem 1,3-dipolar cycloaddition/cyclopropanation process. The preliminary investigations of the asymmetric catalytic version revealed that the biphosphine ligand could be used as the potential efficient chiral ligand.

Solution-phase parallel synthesis of a diverse library of 1,2-dihydroisoquinolines

Synthesis of a 105 membered library of 1,2-dihydroisoquinolines is described. The 1,2-dihydroisoquinoline compounds have been prepared in good yields using a Lewis acid and organocatalyst-cocatalyzed multicomponent reaction of 2-(1-alkynyl)benzaldehydes, amines, and ketones. Various indoles have also been employed as pronucleophiles, furnishing 1-(3-indolyl)-1,2-dihydroisoquinolines. The halogen functionality present in some of the synthesized compounds allows for further diversification by palladium-catalyzed Suzuki−Miyaura and Sonogashira cross-couplings to give more diversified 1,2-dihydroisoquinoline derivatives.

Skeletal diversity via cationic rearrangements of substituted dihydropyrans

Substituted dihydropyrans, easily accessed from a commercially available glycal, undergo acid-catalyzed rearrangement to provide highly functionalized isochroman and dioxabicyclooctane scaffolds.

Green method for the synthesis of highly substituted cyclohexa-1,3-diene, polyhydroindene, polyhydronaphthalene, isochromene, isothiochromene, and isoquinoline derivatives in ionic liquids

An efficient and green method for the synthesis of highly substituted cyclohexa-1,3-diene, polyhydroindene, polyhydronaphthalene, isochromene, isothiochromene, and isoquinoline derivatives has been developed. The synthesis was achieved by using a multicomponent procedure in ionic liquid media. The features of this procedure are characterized by the following: mild reaction conditions, high yields, one-pot procedures, operational simplicity, and environmentally benign conditions.