Acid-catalyzed ring opening in 2-(2-hydroxynaphthalene-1-yl)-pyrrolidine-1-carboxamides: formation of dibenzoxanthenes, diarylmethanes, and calixarenes

One-Pot Synthesis of Novel Dibenzoxanthenes, Diarylbutanes, and Calix[4]resorcinarenes via Consecutive Pyrrolidine Ring-Closure/Ring-Opening Reactions

“…We assumed that pyrrolidine ring opening in strongly acidic media is general for all 2-aryl substituted pyrrolidines. is assumption was supported both by our own observations [27] and synthesis of diphenylbutane derivative upon treatment of N-phenacyl-2-phenylpyrrolidine with triflic acid in benzene solution described by King et al [30] (Scheme 1(C)). Based on this data, we proposed that carrying out the reaction of N-(4,4-diethoxybutyl)ureas with phenols in strongly acidic media would allow us to obtain appropriate diarylbutanes in one-pot procedure via consecutive pyrrolidine ring closure-ring opening processes.…”

“…e oxonium cation A thus formed may further react with phenol molecule, leading to the 2-arylpyrrolidine derivative B as previously described [24]. Subsequent pyrrolidine ring opening in the presence of excess of trifluoroacetic acid followed by interaction with another phenol molecule via the mechanism similar to that of 2-(2hydroxynaphthalene-1-yl)pyrrolidines [27] results in the formation of target compounds E.…”

“…e reaction was carried out in chloroform solution in the presence of 3-fold excess of trifluoroacetic acid, since these conditions were found to be optimal for the ring opening in 2-(2-hydroxynaphthalene-1-yl)pyrrolidines 1 [27]. However, according to NMR data, in this case the yield of target dibenzoxanthenes 5a,c appeared to be rather low.…”

“…2-(2-Hydroxynaphthalen-1-yl)pyrrolidine-1-carboxamides 1a-d were obtained as described previously [24,25]. [27]. To a solution of 1.10 mmol naphthol 4 or 5 in 5 ml of dry chloroform, 0.55 mmol 2-(2hydroxynaphthalen-1-yl)pyrrolidine-1-carboxamides 1 and 2 ml trifluoroacetic acid were added.…”

“…However, this method is inapplicable in case of acetals containing urea moiety, since these compounds are subject to intramolecular cyclization in acidic media [23][24][25][26]. Earlier, we have developed the approach to diarylbutanes, dibenzoxanthenes, and calixarenes possessing urea fragment via acid-catalyzed ring opening of 2-(2hydroxynaphthalene-1-yl)pyrrolidine-1-carboxamides 1 [27,28] (Scheme 1(B)). Although the proposed approach benefits from mild reaction conditions and usage of inexpensive trifluoroacetic acid as catalyst, its certain disadvantage is the necessity of preliminary synthesis of intermediate 2-(2-hydroxynaphthalene-1-yl)pyrrolidines 1.…”