Abstract
In this work, new derivatives (substituted 9-methyl-9-arylxanthenes) of xanthene compounds (5a–l) of possible biological significance were synthesized by developing a new synthesis method. In order to obtain xanthene derivatives, the original alkene compounds to be used as the starting materials were synthesized in four steps using appropriate reactions. A cyclization reaction by intramolecular Friedel–Crafts alkylation was carried out in order to synthesize the desired xanthene derivatives using the alkenes as starting compounds. The intramolecular Friedel–Crafts reaction was catalyzed by trifluoroacetic acid (TFA) and provided some novel substituted 9-methyl-9-arylxanthenes with good yields at room temperature within 6–24 hours. As a result, an alkene compound was used for activation with TFA in the synthesis of xanthene through intramolecular Friedel–Crafts alkylation for the first time.
Highlights
The interest in xanthenes has increased remarkably in recent years due to their wide range of biological and pharmacological properties
As a continuation of our series of works to develop organic Brønsted acid-catalyzed cyclization reactions [41,42], we report a highly efficient intramolecular Friedel–Crafts alkylation (FCA) of appropriate unactivated alkenes with a polyaromatic structure in order to synthesize xanthene derivatives
In the fourth and final step, phenoxydiphenylalkene derivative 4a was prepared by a Wittig reaction, which was carried out using methyltriphenylphosphonium bromide with ketone 3a, in basic medium, at room temperature, and dry THF
Summary
The interest in xanthenes has increased remarkably in recent years due to their wide range of biological and pharmacological properties. The synthesis of arenes using the FCA methods with π-activated alcohols and organocatalysts has begun to be preferred over using conventional reagents, such as organohalogens and transition metal catalysts, which are toxic and require working under harsher conditions [38]. The intramolecular FCA method using π-activated alcohols has frequently been used for xanthene synthesis.
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