ABSTRACT This review describes preparation of a variety of natural products through a key reaction in which a cyclic α-haloether (2) or unsaturated oxonium ion (3) reacts with a carbon nucleophile to form a carbon-carbon bond. Reactions of α-haloethers with malonate anion and organocuprates have been carried out with inversion of configuration at the reactive center, thereby controlling the stereochemistry of the product. Cyclic unsaturated oxonium ions alkylate active methylene compounds under acidic conditions. Novel and improved methods for preparation of oxonium ions and α-haloethers have also been developed.
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