Propargyltitanium

Table 9.22 Effect of alkynyl substituent ofthe efficiency of propargyltitanium additions to aldehydes.

Thermally stable polymers containing titanacyclobutene units have been synthesized by central carbon radical alkylation (Section 2.12.9.2.4) of a l,4-bis( ]3-propargyltitanium)benzene complex. The reaction is remarkably clean and efficient subsequent protonation by ethereal HC1 produces the unsaturated organic polymer and Cp 2TiCl2 <2005MI511>. 

P-Acetylenic alcohols (11, 378). The propargyltitanium reagent derived from 1-trimethylsilyl-3-(tetrahydropyranyloxy)propyne (1) reacts with crotonaldehydes to afford the P-acetylenic alcohol 2 with high stereoselectivity. This alcohol was used in a stcr-eocontrolled synthesis of the natural antibiotic ( )-asperlin (6). 

In organic synthesis, propargyltitanium(rV) complexes are unique among the organometallic reagents in that they perform efficient addition of either alkynic or allenic residues to carbonyl compounds. 

Since this topic will be covered extensively in Part 1 Volume 2, only the main references concerning their preparation and their more significant synthetic applications are recalled at this point. - Hetero-substituted propargyltitanium(IV) reagents are also very useful in the synthesis of natural products. 

---