Alkynyltitanium compounds

The reaction of haloalkynes with one equivalent of 1 affords alkynyltitanium compounds by f5-elimination from the (q2-haloalkyne)Ti(OiPr)2 intermediate, as shown in Scheme 9.5, thus providing an easy access to functionalized alkynyltitaniums [26], When this reaction is carried out in the presence of excess 1, a tri-titanated alkene of the type shown in Scheme 9.5 is generated in excellent yield. This is an interesting method for generating the permetallated terminal alkene [27]. 

The alkynyltitanium complexes TiCI((C=CR) (R typically = alkyl groups) are prepared in situ by reacting 1-alkynes with TiCU in the presence of Et3N. The synthetic potential of these compounds has been illustrated in reactions with a number of electrophiles. In the presence of terminal alkynes, symmetrical 1,3-diynes are formed. The reaction with chlorodiphenylphosphine produces the corresponding alkynyl phosphine, while treatment with triethylphosphite affords tris(phenylethynyl) phosphine by substitution of the three alkoxo groups. The reaction with trimethyl orthoformate gives acetals.6-9... 

Metallated titanacyclopropene derivatives (Scheme 97) can be prepared from the diisopropoxo( 72-propene) titanium compound or from TiCp2( 1-butene) and alkynyltitanium species.185... 

The chemoselective reaction between a functionalized alkynyltitanium derivatives and a functionalized electrophile has been performed for the preparation of polyfunctional compounds in a one-pot procedure (Scheme 12.57) [75]. 

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