Stereocontrolled Synthesis of Tungsten−π-Allyl Complexes Comprising Two Remoted Alcohols

[[abstract]]Organic lithium reagents add to the carbonyl group of CpW(CO)(2)( eta (3)-gamma -lactonyl) 4a to give the pi -allyl eta (3)-hydroxycarbonyl tungsten complexes 5a-5d with good yields (79-94%). An X-ray study of compound 5a revealed the acetyl group has pi -delocalization with a tungsten-pi -allyl group. A subsequent reaction of 5a with DIBAL-H, RMgBr (R = Ph, Et), and (BuLi)-Bu-n gave the diols CpW(CO)(2)[(3R*,4S*)-pi -2-CMe(OH)R-CH2CCHCMe(OH)] (R = H 6a, Ph 6b, Et 6c, Bu-n 6d) as a single diastereomer; the yields were 64%-86%. The acyl group of CpW(CO)(2)[(3R*,4S*)-pi -2-COMe-CH2CCHCMe(OTBS)] (7) was deprotonated by LDA at -78 degreesC to form an enolate that condensed with RCHO (R = Pr-i, Bu-i) to form a pair of aldol products 8a,8b and 9a,9b, which were separated by column chromatography. In the presence of (n)-Bu2BOTf, the diastereoselectivities of 8b and 9b were improved significantly. The structures of these aldol products were elucidated by X-ray diffraction study of the representative product 8b.[[fileno]]2010327010097[[department]]化學