Titanium Compounds Organotitanium reagents

However, in a comprehensive study, Seebach and coworkers have shown the usefulness of titanium and zirconium alkyls as selective nucleophilic reagents.106,107 Typically compounds of the type (RO)3MR (M = Ti, Zr) are reacted with aldehydes or ketones to yield asymmetric alkoxides (equation 32),107 The method has been extended to allow enantioselective addition using chiral organotitanium reagents where the chirality is imposed by the initial alkoxide substituents.107,108... 

In addition to the aforementioned X-ray analysis to disclose the structure of a few crystalline titanium chelates, and NMR studies have been performed to provide evidence for the chelation structure of a- and /1-oxycarbonyl compounds in solution [33-35]. Approximate solution structures for -alkoxyaldehydes are as shown in Fig. 7 [34]. The mechanism of chelation-controlled reactions of organotitanium reagents has been investigated experimentally [5] and theoretically [36], and the subject has been reviewed [10]. The formation of a chelate structure with titanium metal at the center plays a pivotal role in determining the reactivity and selectivity [37] in many synthetic reactions as shown in the following discussion. 

Recently, many reviews of organotitanium compounds on reagents for organo-synthetic reaction have been reported, especially on low valent titanium compounds [34,52-61]. 

Organotitanium and -zirconium chemistry already has an established place in organic synthesis and many reactions are covered elsewhere in the Practical Approach series. Examples include reductive coupling of carbonyl compounds with low valent titanium to form 1,2-diols or alkenes methylenation of ester carbonyl groups with titanocene methylidene (Cp2Ti=CH2) zirconium-catalysed methylalumination of alkynes and hydrozirconation of alkynes and alkenes with the Schwartz reagent, Cp2ZrHCl. ... 

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