Lanthanocene catalysts cyclization

Enantioselective cyclizations of amino-octadiene with chiral lanthanocene catalysts provide a facile access to (-l-)-coniine with 63% ee after hydrogenolysis of the... 

The lanthanocene catalysts display high catalytic activity, which is proportional to the ionic radius of the rare earth metal (Table 11.1). The rate of cyclization depends on the ring size of the azacyclic product (5 > 6 7) and the presence of rate... 

If the alkene is connected to the phosphine, hydrophosphination results in cyclization, as observed for a series of lanthanocene catalysts. DPT and experimental studies were consistent with the mechanism of Scheme 19, where P-C bond formation occurs by the approximately thermoneutral insertion of an alkene into a... 

Initial studies focused on lanthanocene-based catalyst systems that proofed to be efficient in the exo-specific cyclization of terminal aminoalkenes to form five-, six-, and seven-membered azacycles (Scheme 2). The reactions are predictably faster for the formation of smaller five-membered rings and in the presence of em-dialkyl substituents [117]. An increasing metal ionic radius and a more open coordination sphere, for example, in onra-lanthanocenes, are also beneficial for higher cyclization rates [103]. A further increase in catalytic activity is observed when sterically more open and more electrophilic CGC 17 (Fig. 15) are applied [118]. 

Taking into account that thermal conversion of diamido to imido species is not accessible to BnjCyclam zirconium complexes, the cyclization reaction is likely to occur by 1,2-insertion of the olefin moiety in the Zr-N bond (Scheme 25.4). This pathway was initially proposed by Tobin Marks for lanthanocene and constrained geometry zirconium complexes and was more recently also suggested for other group 4 metal catalysts [15, 16]. The activation of the olefin toward insertion may... 

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