Diastereo- and enantioselective synthesis of allenylcarbinols through SE2' addition of transient nonracemic propargylic stannanes to aldehydes.
作者:James A. Marshall、Richard H. Yu、Jolyon F. Perkins
DOI:10.1021/jo00122a040
日期:1995.9
The nonracemic allenylstannane 1c was prepared by S(N)2' displacement of mesylate 8 with Bu(3)-SnLi-CuBr . SMe(2). Treatment of this stannane with BuSnCl(3) followed by addition of isobutyraldehyde at -40 degrees C afforded the syn allenylcarbinol 4c in nearly 80% yield, The nonracemic aldehydes (S)- and (R)-16 were similarly converted to the adducts 17 and 18 in high yield with good to excellent diastereoselectivity. Best results were obtained when hexane was employed as the solvent, A reaction pathway is proposed to account for the steric preference of these additions, The allenylcarbinols were converted stereospecifically to the cis-2,5-dihydrofurans 23-25 upon treatment with catalytic AgNO3 in acetone.
Intramolecular Diels−Alder Reactions of Optically Active Allenic Ketones: Chirality Transfer in the Preparation of Substituted Oxa-Bridged Octalones
作者:Michael E. Jung、Sun-Joon Min
DOI:10.1021/ja052771e
日期:2005.8.1
reaction of allenic ketones containing a furyl unit (IMDAF) to generate oxatricyclic systems in good yields is described. The alkene dienophiles 1ab give poor yields of the cycloadducts 2ab, presumably due to the facile retro Diels-Alder reaction. However, the analogous allenic dienophile 7 afforded the desired cycloadduct 8 in 91% yield on treatment with dimethylaluminum chloride. When the allene bears