Allenyl titanium reagent

Propargylic ethers undergo directed lithiation and subsequent transmetallation to afford oxygenated allenyl titanium reagents. Subsequent addition of aldehydes gives rise to various homopropargylic alcohol adducts as mixtures favoring the anti dia-stereomers (Tables 9.18 and 9.19) [29, 30]... 

CH3CH=C=C. (1). This allenyl titanium reagent is prepared... 

When the leaving group is in a /3-position, as in 86, allenyl species are formed. It is therefore easy to prepare the allenyl titanium reagents having a functional group as exemplified in Scheme 12.58. Functionalized homopropargyl alcohols are obtained by their reaction with carbonyl compounds [76]. 

Analogous to the allylation with allylsilanes and -stannanes, the transformations, vinylallylation, propargylation, allenylation, alkenylation, alkynylation, and arylation, are viable by the use of an appropriate reagent in the presence of a titanium Lewis acid these are surveyed in the review articles cited both in the Introduction and in this section. The stereochemistry of the reaction of a (vinylallyl)silane in the presence of TiCU has been reported [234]. Equation (113) shows that the major reaction of this silane and isobutyraldehyde occurred mainly in the anti sense with a ratio of anti to syn attack of 90 10 at the terminus remote from the silyl group. Essentially the same stereochemical outcome was observed for the same reaction with the corresponding trimethylsilyl derivative. The intramolecular reaction with an acetal, however, proceeded less selectively the anti syn ratio was 60 40 (Eq. 114) [234]. 

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