Titanium-induced syntheses of furans, benzofurans and indoles

Abstract

Highly reactive titanium on graphite as the reagent of choice promotes intramolecular McMurry type reactions of acyloxy- and acylamido carbonyl compounds affording furans, benzofurans and indoles in good to excellent yields. A variety of reducible groups in the substrates is tolerated (e.g. -F, -Cl, -Br, -I, -CF 3, -OMe, -CN, -thiophenyl, -COOR, -CONR 2) and strained products such as 11h can be obtained, the X-ray analysis of which is reported. The experimental results indicate the possible formation of dianions from the aromatic aldehydes or ketones as reactive intermediates which attack the ester or amide functions in their proximity, rather than a radical path via ketyls.