Zirconocene-mediated synthesis of cyclobutabenzenes.

A new, mild, one-pot method for the synthesis of cyclobutabenzenes by the zirconium-promoted cross-coupling reaction of aryllithium compounds and alkenyl bromides is reported. Formation of an arynezirconocene complex and its regioselective coupling with an alkenyl bromide are the key steps of the process. This method allows the regio- and diastereoselective synthesis of functionalized cyclobutabenzene derivatives from simple and easily available starting materials.

Medium-sized carbocycles by a zirconocene-catalyzed tandem formal ring expansion-magnesation reaction of alkenyl-substituted cyclic enol ethers.

A new regio- and stereoselective zirconocene-catalyzed reaction for the synthesis of medium-sized rings is described. The global reaction supposes a formal ring expansion of a cyclic enol ether to give a functionalized carbocycle.

Coupling reactions of zirconocene complexes and heterosubstituted alkenes.

This tutorial review surveys recent advances in the field of zirconium promoted coupling reactions of unsaturated molecules (and/or organolithium compounds) and heterosubstituted alkenes. This reaction has recently emerged as a powerful tool in organic chemistry to access a variety of synthetically useful building blocks not easily available by other methods. In particular, three different reaction pathways are discussed: i) the reaction involving alkyne-zirconocene and aryne-zirconocene complexes which allows access to dienyl and aryl zirconocene complexes; ii) the reaction of alkene-zirconocene complexes and enol ethers which has shown to be highly dependent on the structure of the enol ether used, allowing the synthesis of simple vinyl zirconocenes or multicomponent coupling products, and; iii) the reaction involving imine-zirconocene complexes which supposes a new entry to allylic amines.

Zirconium-mediated cross-coupling of terminal alkynes and vinyl bromides: selective synthesis of cyclobutene and 1,3-diene derivatives.

A diastereoselective synthesis of 1,3-butadiene or cyclobutene derivatives by a zirconium-mediated reaction of alkenyllithium compounds and vinyl bromides is reported. The key steps involve the generation of zirconocene-alkyne complexes from haloalkenes and subsequent coupling with alkenyl bromides. Thus, formally the process supposes the cross-coupling reaction between a terminal alkyne and an alkenyl bromide. Moreover, the use of butyl vinyl ether instead of vinyl bromide as the unsaturated system allows an alternative access to different 1,3-butadiene regioisomers.

Zirconium-mediated coupling reactions of amines and enol or allyl ethers: synthesis of allyl- and homoallylamines.

An easy and efficient zirconium-mediated synthesis of allylamines from simple amines and enol ethers is described. This strategy also allows the synthesis of amino alcohol derivatives containing a Z double bond in their structure when 2,3-dihydrofuran is used. Simple conventional modification of these amino alcohols leads to 2-substituted piperidine derivatives. By applying this approach, a formal total synthesis of the alkaloid coniine is easily achieved from a protected butylamine. Finally, the zirconium-mediated reaction of amines and allyl phenyl ether furnishes homoallylamines or amino ethers depending on the structure of the starting amine.