Titanocene alkenylidene

As noted above, titanocene-alkylidenes can be prepared using various methods and starting materials. Like the methylidene complex, higher alkylidene complexes are useful for the transformation of carbonyl compounds to highly substituted olefins. Ketones and aldehydes are converted into substituted allenes by treatment with titanocene-alkenylidenes prepared by olefin metathesis between titanocene-methylidene and substituted allenes (see Scheme 14.7) [17]. Titanocene-alkenylidene complexes can also be prepared from... 

The formation of highly substituted titanacyclobutenes utilizing titanocene-alkylidenes has been investigated (Scheme 14.33). Alkylidenetitanacyclobutenes 76 are produced by the reaction of titanocene-alkenylidene complexes with alkynes [76]. The alkenylcydopro-pane 77 can be synthesized by thermolysis of dicydopropyltitanocene in the presence of diphenylacetylene, which is assumed to proceed through formation of the titanacyclobutene 78 [25c],... 

When valuable alkenyl groups are used, the use of alkyl alkenyl titanocene prepared from the monochlorotitanocene also leads to the unstable titanocene alkenylidene intermediate that is similarly trapped in situ by the carbonyl compound [66]. 

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