THE ASYMMETRIC VINYLOGOUS MUKAIYAMA ALDOL REACTION

摘要

Aldol reactions are among the most prominent and most frequently applied transformations in synthetic organic chemistry because they assemble polyketide fragments of important biologically active compounds such as antibiotics and antitumor compounds. These reactions are valuable not only because they generate new carbon-carbon bonds, but also because they create new stereogenic centers. The most frequently applied methods for aldol reactions often parallel the processes seen in the biosynthesis of polyketide natural products. In the biosynthesis, acetate or propionate units are added; subsequently, a series of further transformations (reductions, eliminations, hydrogenations) are performed by large polyketide synthetases to provide the substrate for the next aldol reaction. The laboratory synthesis mostly follows this modular approach by adding acetate and propionate fragments followed by reduction and oxidation steps, often coupled with extensive protecting group shuffling and additional chain-extension transformations, such as Horner-Wadsworth-Emmons (HWE) reactions (Scheme 1).