Fused ring systems derived from reactions of half-open titanocenes with diynes: Syntheses, characterization, cage rearrangements, and structural studies

The reactions of several α,ω-diynes with half-open titanocene complexes [M(C5H5)(2,4-C7H11)(PR3)] (C7H11 = dimethylpentadienyl) lead to 5 + 2 + 2 ring constructions, yielding nine-membered rings fused to four-membered and larger rings. These reactions tolerate significant functionalization, even allowing for the presence of heteroatoms such as oxygen and nitrogen. The nine-membered rings provide both allyl and diene coordination to the Ti(C5H5) fragments, resulting in 16 electron configurations. On standing, these species undergo cage rearrangements, via Csingle bondC bond activation reactions. Structural data have been obtained for a number of the fused ring species, as well as one of the rearrangement products.