Benzopyranoisoxazolidines : Useful Chiral Auxiliaries for Asymmetric Synthesis

Abstract

New chiral auxiliaries based on the isoxazolidine skeleton have been developed. Characteristic feature of these auxiliaries are : 1) High reactivity for asymmetric alkylations. 2) Acylation of the auxiliary with an acid chloride and an amine, or DCC condensation. 3) One step transformation of the reaction products to the corresponding chiral alcohols, aldehydes and ketones without loss of the stereochemical integrity with the recovery of the auxiliary. Asymmetric alkylation of chiral β-substituted alkanols via their triflates lead to the easy access to the “reduced polypropionate units” as well as the first synthesis of the marine natural product (+) -siphonarienone. Enantiomerically pure axially dissymmetric cyclohexylidene compounds were synthesized using asymmetric Horner-Emmons reaction of the phosphonate derived from the auxilliary.