Synthesis of Biaryls, Fluorenones, Cyclopenta[def]phenanthren-4-ones, and Benzophenones Based on Formal [3+3] Cyclocondensations of 1,3-Bis(silyloxy)buta-1,3-dienes with 3-(Silyloxy)-2-en-1-ones

Functionalized fluorenones were efficiently prepared in four steps. The [3+3] cyclization of 1,3-bis(silyloxy)buta-1,3-dienes with 3-(silyloxy)-2-en-1-ones afforded salicylates that were transformed into their enol triflates. The Suzuki cross-coupling reaction of the latter with arylboronic acids afforded 2-(methoxycarbonyl)biaryls that were Subsequently transformed into the target molecules by intramolecular Friedel-Crafts acylation. In addition, 1-hydroxyfluorenones were prepared by cyclization of 3-aryl-3-(silyloxy)-2-en-1-ones with 1,3-bis(silyloxy)buta-1,3-dienes and Subsequent intramolecular Friedel-Crafts acylation of the 6-aryl-salicylates thus formed. In this context, the synthesis of novel cyclopenta[def]phenanthren-4-ones is reported. In addition, the synthesis of functionalized benzophenones is reported.