RESUMO
Two new efficient methods for the regioselective homocoupling of allylic halides using either catalytic TiIII or the combination Mn/ZrIV catalyst have been developed. The regio- and stereoselectivity of the process proved to increase significantly when the Mn/ZrIV catalyst is used as the coupling reagent and when cyclic substituted allylic halides are used as substrates. The use of Lewis acids such as collidine hydrochloride allowed the quantity of catalyst to be lowered up to 0.05 equiv. We have proved the utility of these protocols with the synthesis of different terpenoids such as (+)-beta-onoceradiene (1), (+)-beta-onocerine (2), squalene (5), and advanced key-intermediates in the syntheses of (+)-cymbodiacetal (3) and dimeric ent-kauranoids as xindongnin M (4a).
Assuntos
Manganês/química , Terpenos/síntese química , Titânio/química , Zircônio/química , Catálise , Diterpenos do Tipo Caurano/síntese química , Diterpenos do Tipo Caurano/química , Hidrocarbonetos Halogenados/síntese química , Hidrocarbonetos Halogenados/química , Monoterpenos , Compostos Organometálicos/síntese química , Compostos Organometálicos/química , Esqualeno/análogos & derivados , Esqualeno/síntese química , Esqualeno/química , Terpenos/química , Triterpenos/síntese química , Triterpenos/químicaRESUMO
Titanocene monochloride catalyzes the homocoupling of benzylic halides and benzylic gem-dibromides to give the corresponding bibenzyl and stilbenyl systems. Exposure of benzylic bromides to Ti(III) in the presence of aldehydes gave rise to the Barbier-type products. Examples of the utility of the herein described processes are included.
