Synthesis of the 4,10-Dihydro-3H-pyridazino[1,6-b]isoquinolin-10-one System by a Furan Recyclization Reaction S y n t h e s i s o f t h e 4 , 1 0 -D i h y d r o -3 H -p y r i d a z i n o [ 1 , 6 -b ] i s o q u i n o l i n -1 0 -o n e S y s t e mAbstract: The novel 4,10-dihydro-3H-pyridazino[1,6-b]isoquinolin-10-one heterocyclic system was synthesized by acid-catalyzed recyclization of 2-(difurylmethyl)benzohydrazides as well as by recyclization of (2-carboxyaryl)difurylmethanes to isocoumarins followed by the reaction with hydrazine hydrate.

in Wiley Online Library (wileyonlinelibrary.com).For the first time, tetracyclic compounds, namely, furo[2 0 ,3 0 :3,4]cyclohepta[1,2-b]indoles were synthesized by recyclization of ortho-substituted aryldifurylmethanes containing tert-butyl groups at C5 positions of the furan rings. It was shown that [2-(benzoylamino)phenyl]bis(5-tert-butyl-2-furyl)methanes 12 are transformed into tetracycles 15 at room temperature under treatment with POCl 3 in benzene solution containing some drops of water. The reaction proceeds via the intermediate formation of 1-benzoylamino-3-(5-tert-butyl-2-furyl)-2-(4,4-dimethyl-3-oxopentyl)indoles 14 which can be isolated from the reaction mixture. The method is very simple but its application is restricted due to side reactions if electron-releasing groups are present in 12. On the other hand, the decrease of electron density on furan ring in the starting compounds (for example, the use of [2-X-phenyl]difurylmethanes (where X ¼ tosylamino or hydroxy group) prevents cyclization under the studied reaction conditions. As a result, corresponding ketones are formed as products of recyclization.

A new approach to highly functionalized quinolines is proposed. This approach is based on the electrophilic recyclization of 2-[2-(acylamino)benzyl]furans under the Bischler-Napieralski reaction conditions.

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Synthesis of Tetracyclic System of 2,4-Di(tert-butyl)-6,7-dihydrofuro[2',3':3,4]cyclohepta[1,2-b]indole. -For the first time the title compounds (II) and (VI) are synthesized by the presented method. The compounds (IV) and (VII) present the intermediates, whereas the compound (IV) does not react to the corresponding tetracycle. -(BUTIN*, A. V.; KOSTYUKOVA, O. N.; TSIUNCHIK, F. A.; UCHUSKIN, M. G.; SERDYUK, O. V.; TRUSHKOV, I. V.; J. Heterocycl. Chem. 48 (2011) 3, 684-690, http://dx.