Reactions of dicarbanion equivalents generated from complexation of 1,3-dienes on Ti(II) moiety
摘要:
Conjugated dienes are able to react as 1,2- or 1,4-dicarbanions by coordination on Ti(II) moiety. These two possibilities are exemplified in this letter with isoprene, myrcene and several aldehydes to give 1,4- and 1,6-diols. When allowed to react with esters at room temperature, the titanium-diene complexes lead to cyclopentenol derivatives. Surprisingly, when this reaction is performed at lower temperature (-40 degrees C), allylic ketones are formed with high regio and diastereoselectivities. (c) 2006 Elsevier Ltd. All rights reserved.
The cathodic cyclocoupling of 1,3-dienes 1 with aliphatic esters 2 is promoted by a magnesium electrode and yields homologs of 3-cyclopentenol. Under similar reaction conditions, the coupling of styrenes with 2 affords 2-phenylcyclopropanol derivatives, and this coupling reaction has been successfully applied to the synthesis of ar-dihydroturmerone and curcumone.