Chlorozirconium complexes

The first organometallic zirconium complexes to be prepared all contained Zr( 1V) and were reported almost contemporaneously. The reaction of Zr(TPP)-(OAc)2 with RLi or RMgBr produced the dialkyl complexes Zr(TPP)R2 (R = Me, Et, n-Bu or Ph), characterized by. spectroscopy. The development of the chlorozirconium complexes opened up the chemistry further, with... 

The alkyl chlorozirconium compounds undergo a variety of useful reactions, as can be seen from Figure 31-1. Similar reactions also can be carried out with alkynes by way of complexes such as (Cp)2Zr(Cl)CFf=CH2. 

The high syn stereoselectivity attained in zirconium enolate aldol reactions has proved useful in complex natural product synthesis. The zirconium-mediated aldol reaction of the chiral ethyl ketone (9) with a chiral aldehyde has been used by Masamune et al. to give selectively adduct (10), which was further elaborated into the ansa chain of rifamycin S (equation l).5 Good enolate diastereofacial selectivity is also obtained here and leads to a predominance of one of the two possible syn adducts. A zirconium enolate aldol reaction also features in the Deslongchamps formal total synthesis of erythromycin A, where the di(cyclopentadienyl)chlorozirconium enolate from methyl propionate adds with high levels of Cram selectivity to the chiral aldehyde (11) to give the syn adduct (12 equation 2).6 A further example is... 

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See also in sourсe #XX -- [ ]

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