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In 1969 by acad. Babayan A.T. and prof. Chukhajian E.O. with coworkers was discovered that ammonium salts, containing groups of allylic or propargylic type along with alkenylprop-2-ynylic, even in the presence of 0,2 mol of alkali per mol of initial salt at room temperature undergo with self-heating intramolecular cyclization; reaction ends within 5-10 min, forming potentially bioactive isoindolinium and 3a,4-dihydroisoindolinium bromides with quantitative yieds.1 Later it was shown that instead of expected last salts were obtained their isomeric forms – 2,6,7,7a-tetrahydro-1H-isoindolinium bromides.2
In above mentioned conditions with self-heating undergo cyclization also ammonium salts containing propargylic type group alongside with 3-arylprop-2-ynylic fragment leading to formation of bioactive di-, three- and polycyclic isoindolinium and dihydroisoindolinium salts.3 As a result of cyclization of –(4-hydroxybut-2-ynyl)(3-alkenyl- or 3-arylprop-2-ynyl)ammonium chlorides–hydroxymethylisoindolinium salts and their condensed analogs are obtained.
In 2003 by us was discovered that mentioned salts in water-base cleavage conditions undergo intramolecular recyclization leading to derivatives of 1,3-dihydrobenzo[c]furans, formation of which includes the stages of nucleophylic attack of an alkoxy anion on partially charged carbon atom of isoindolinium cycle with the breaking of N-C and formation of C-O-C bond.3, 4 It was established that voluminous substituents at nitrogen atom and in aromatic ring and also the increase of the number of aromatic cycles favorably act on recyclization. In contrast to intermolecular recyclization the process is not accompanied by any expansion or contraction of the cycle, and instead of isoindolinium cycle pharmacophore 1,3-dihydrofuranic ring is formed. Intramolecular recyclization is a domino process, has general character and besides of fundamental has also preparative significance. It was known that some of derivatives of 1,3-dihydrobenzo[c]furans are a part of molecules of diterpens and contained in sea sponges and algas and used in clinical practice as antidepressants and etc.
Base catalized intramolecular cyclization and recyclization are new directions in organic chemistry. Among cyclic products are representatives with high pharmacological activity.3 Activity is protected by numerous copyrights of Soviet Union and patents of Republic of Armenia.
The acquaintance with the results of base catalized intramolecular cyclization and recyclization enlarge the horizon of each organic chemist in this field.
Compounds which are result of these reactions can be objects of pharmacological investigations for creation of medicinal preparats and also representatives with new pharmacological activities.