Indenes are important core structures in organic chemistry. Few simple arylallenes have been used to construct indene skeletons by Friedel-Crafts reaction. Lewis acid catalyzed reaction of ethenetricarboxylates 1 and arylallenes has been examined in this study. The reaction of arylallenes and ethenetricarboxylate triesters with SnCl(4) gave indene derivatives efficiently, via a conjugate addition/Friedel-Crafts cyclization reaction. On the other hand, the reactions of 1,1-diethyl 2-hydrogen ethenetricarboxylate and arylallenes or alkylallenes with SnCl(4) at -78 degrees C or room temperature and subsequent treatment with Et(3)N gave gamma-lactones. The reactions of triethyl ethenetricarboxylate and 1,1-dialkylallenes with SnCl(4) at room temperature also gave gamma-lactones.

The Lewis acid promoted reaction of 1,1-diarylallenes with ketone derivatives was examined. The tin(IV) chloride promoted reaction of diarylallenes with vinyl ketones gave indene derivatives through a conjugate addition/cyclization reaction. The reaction of diphenylallene with diethyl oxomalonate in the presence of one equivalent of tin(IV) chloride at -40 °C gave diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate as the major product through a carbonyl addition/cyclization reaction, whereas the same reactants in the presence of 0.2 equivalents of tin(IV) chloride at 80°C gave diethyl (3-phenyl-1H-inden-2-yl)malonate. Diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate was also converted into the latter product on heating at 80 °C in the presence of 0.2 equivalents of tin(IV) chloride.

Lewis Acid Promoted Reactions of Ethenetricarboxylates with Allenes: Synthesis of Indenes and γ-Lactones via Conjugate Addition/Cyclization Reaction. -Lewis acid promoted treatment of ethenetricarboxylates and the nitrile (Ie) with arylallenes allows new access to indenes. The reaction with 1,1-dialkylallenes, on the other hand, provides γ-lactones. The latter are also available from the acid (Ia) and aryl-and diarylallenes. -(YAMAZAKI*, S.; YAMAMOTO, Y.; FUKUSHIMA, Y.; TAKEBAYASHI, M.; UKAI, T.; MIKATA, Y.; J. Org. Chem. 75 (2010) 15, 5216-5222,