A Convenient and Asymmetric Protocol for the Synthesis of Natural Products Containing Chiral Alkyl Chains via Zr-Catalyzed Asymmetric Carboalumination of Alkenes. Synthesis of Phytol and Vitamins E and K
摘要:
[GRAPHICS]A convenient and asymmetric protocol for the synthesis of chiral oligoisoprenoids is described. Typically, a C-14 vitamin E side chain 5 was synthesized in 47% yield over four steps. Isomeric purity of 5 was upgraded to > 99% R at C-2 and 97% R at C-6 by the statistical formation of stereoisomeric p-phenylenebisurethanes and their diastereomeric separation. In addition, phytol and vitamin K were synthesized in 21% and 28% overall yields, respectively, over five steps from 1.
The (6-hydroxy-chroman-2-yl) acetic or carboxylic acid derivatives useful as antioxidants and a method for preparing these derivatives from hydroquinones and intermediates in this synthesis as well as the use of these derivatives as intermediates in the preparation of optically active alpha-tocopherol.