No abstract

A variety of 1,2‐dihydroisoquinoline derivatives 3 have been prepared in good to high yields by the AgOTf‐catalyzed reaction of ortho‐alkynylaryl aldimines 1 with various pronucleophiles 2 (see scheme). Treatment of 1 with a stoichiometric amount of AgOTf followed by protonation with TfOH produced 4, which suggests the formation of an isoquinolinium intermediate in the present direct addition reaction. Tf=trifluoromethanesulfonyl.

Treatment of beta-keto esters with terminal acetylenes in the presence of a catalytic amount of a manganese complex, MnBr(CO)5, and molecular sieves, gave multisubstituted aromatic compounds in good to excellent yields. This reaction employs [2 + 2 + 2] cycloaddition of beta-keto esters and 2 equiv of terminal acetylenes with dehydration. In the case of a 1,3-diketone, the corresponding acetophenone derivative and its deacylated compound can be synthesized selectively.

We have succeeded in the development of three approaches to the synthesis of aromatic compounds from 1,3-dicarbonyl compounds and alkynes. The first approach is a manganese-catalyzed [2+2+2] cycloaddition between 1,3-dicarbonyl compounds, which have no substituents at the active methylene moiety, and terminal alkynes. This reaction proceeds with high regioselectivity when aryl acetylenes are employed as the alkyne component. The second approach is a rhenium- or manganese-catalyzed formal [2+1+2+1] cycloaddition between beta-keto esters and two kinds of alkynes. In this reaction, the aromatic compounds are obtained by the following reaction sequence: (1) insertion of the first alkyne into a carbon-carbon single bond of a beta-keto ester, (2) formation of 2-pyranones via intramolecular cyclization with the elimination of ethanol, and (3) Diels-Alder reaction between the formed 2-pyranone and the second alkyne. This reaction provides multisubstituted aromatic compounds in a regioselective manner. The third approach is a rhenium-catalyzed formal [2+2+1+1] cycloaddition reaction from two 1,3-diketones and one alkyne. In this reaction, the aromatic skeleton is constructed from three carbons of the first 1,3-diketone, two carbons of the alkyne, and one carbon of the second 1,3-diketone.

Three-component reactions with ortho-alkynylbenzaldehydes, primary amines, and pronucleophiles (Nu-H), such as CHCl3, proceeded to give 1,2-dihydroisoquinoline derivatives in good to high yields in the absence of any catalysts under mild reaction conditions.