A highly stereoselective pinacolization of aromatic and α, β-unsaturated aldehydes.dta mediated by titanium(III)-magnesium(II) complex

✍ Scribed by Yuichi Handa; Junji Inanaga

• Publisher: Elsevier Science
• Year: 1987
• Tongue: French
• Weight: 130 KB
• Volume: 28
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)96822-9

✦ Synopsis

Reduction of Cp2TiC12 with s-BuMgCl in THF gave a greenish deep brown solution which has been found to promote the reductive homocoupling of aromatic and a+-unsaturated aldehydes to yield symmetrical 1,2-diols with high threo-selectivity. threo-1,2-Diols have, after resolution, frequently been utilized as auxiliaries of asymmetric syntheses. 11 Although a number of methods have so far been developed for the reductive coupling of carbonyl compounds, 2) selective pinacolization to threo-diols has only been found with stannylene precursors 3) or with an "active titanium(III)-reagent" prepared from Tic14 and n-BuLi. 4) However, the stereoselectivity of the former is not so satisfactory and the latter sometimes suffers from substrate-dependence. We report here a more general and highly threo-selective synthesis of symmetrical 1,2-diols by the aid of titanium(III)-Mg(I1) complex. Cyclopentadieny-bound titanium(II1) reagents 5,6) used, were prepared by the reduction of Cp2TiC12 with appropriate reducing agents. 7) As can be seen in Table 1, the stereoselectivity in the pinacolization of benzaldehyde greatly depended upon the co-existing metal ion