Synthesis of ?,?-unsaturated amines of the tetrahydropyran series

Synthesis and intramolecular recyclization of 2,2-dialkyl-6-chloro-4-hydroxymethyl-benzo[f]isoindolinium salts

“…Here, as before [2][3][4][5], the products from recyclization of compounds 2a-c -4-dialkylaminomethyl-8-chloro-1,3-dihydronaphtho[1,2-c]furans 3a-c -are also obtained with yields of 10-15%. The latter are formed with yields of 62-68% from the salts 2a-c by the action of a twofold molar excess of KOH in aqueous solution with heating (80-85°C), and with subsequent cyclization and recyclization without isolation of the salts 2a-c the total yields of the amines 3a-c amount to 75-82% [2][3][4].…”

“…While studying the question of the stability of the above-mentioned salts under the conditions of aqueous alkaline cleavage we discovered intramolecular recyclization, which included a stage with cleavage of the isoquinoline ring by the action of the alkoxide ion formed in the alkaline medium and the formation of a dihydrofuran ring [2][3][4][5]. It was established that the recyclization process was facilitated by increase in the number of aromatic rings and by the presence of a methyl substituent in the benzene ring.…”

“…The transformation of the salts 2a-c into the amines 3a-c takes 1.0-1.5 h, whereas 2.0-3.5 h is required for the recyclization of the previously investigated 2,2-dialkyl-4-hydroxymethylisoindolinium and 2,2-dialkyl-4-hydroxymethylbenzo[f]isoindolinium salts [2,4]. The ease of recyclization of the salts with substituents in the aromatic ring [3] and the salts with the phenanthrene ring [5] compared with the 2,2-dialkyl-4-hydroxymethylisoindolinium analogs is explained by the higher aromaticity of the benzene ring.…”

“…In the presence of 0.2 mol of aqueous KOH to 1 mol of the initial salt dialkyl(2-butynyl-4-hydroxy)-(3-R 1 -propargyl)ammonium salts (R 1 = Ph, vinyl, or isopropyl) undergo cyclization, forming 2,2-dialkyl-4-hydroxymethylisoindolinium and 2,2-dialkyl-4-hydroxymethylbenzo[f]isoindolinium salts [1][2][3].…”

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In the presence of 0.2 mol of aqueous KOH to 1 mol of the initial salt dialkyl(2-butynyl-4-hydroxy)-(3-R 1 -propargyl)ammonium salts (R 1 = Ph, vinyl, or isopropyl) undergo cyclization, forming 2,2-dialkyl-4-hydroxymethylisoindolinium and 2,2-dialkyl-4-hydroxymethylbenzo[f]isoindolinium salts [1][2][3].While studying the question of the stability of the above-mentioned salts under the conditions of aqueous alkaline cleavage we discovered intramolecular recyclization, which included a stage with cleavage of the isoquinoline ring by the action of the alkoxide ion formed in the alkaline medium and the formation of a dihydrofuran ring [2][3][4][5]. It was established that the recyclization process was facilitated by increase in the number of aromatic rings and by the presence of a methyl substituent in the benzene ring.

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