Synthesis of tetracyclic system of 2,4‐di(tert‐butyl)‐6,7‐dihydrofuro[2′,3′:3,4]cyclohepta[1,2‐b]indole

Abstract

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.

Furan's Gambit: Electrophile‐Attack‐Triggered Sacrifice of Furan Rings for the Intramolecular Construction of Azaheterocycles

“…Methoxy groups in the aniline moiety accelerate not only the second cyclization, but also side processes leading to the tarring of the reaction mixture. A significant decrease in POCl 3 loading led to a reduction of the resinification; in this case ketone 22 was obtained as a single product in 54 % yield 15b…”

“…In contrast to benzanilides 20 , the corresponding N ‐tosylanilines 23 gave no tetracyclic products upon treatment with the POCl 3 /H 2 O system 15b. Under these reaction conditions, as well as upon treatment with ethanolic HCl or HCl/AcOH,16 they formed 3‐furyl‐2‐(3‐oxoalkyl)‐1‐tosylindoles 24 exclusively (Scheme ).…”

Furan Ring Opening - Pyridine Ring Closure: New Route to Quinolines under the Bischler-Napieralski Reaction Conditions

“…N-{2-[Bis(5-tert-butyl-2-furyl)methyl]phenyl}-4-bromobenzamide (1k) 27 Pale yellow cubes; yield: 2.79 g (87%); mp 155-156°C.…”