Epoxide ring cleavage enantioselective

Reaction of epoxides with nitrogen nucleophiles affords a variety of P-hydroxyamines and their equivalents. Comprehensive review articles have been published. In conjunction with the development of diastereoselective and enantioselective syntheses of epoxy alcohols, selective oxirane ring cleavage of 2,3-epoxy alcohols and carboxylates by nitrogen nucleophiles has become a versatile route to various amines and their equivalents. For details, the reader is referred to refs. lOSc and 103d. 

When bomeol or camphor is heated with solid potassium hydroxide to 250-280 °C, ring cleavage of the bicyclic system occurs and the product, campholic acid 68, can be isolated in high yield65-67. Thus, (-)-borneol gives ( + )-campholic acid [( + )-68], which has been used as the hydroxamic acid derivative as a chiral ligand for a vanadium catalyst in the enantioselective epoxidation of allylic alcohols (Section D.4.5.2.4.). 

Under comparatively drastic reaction conditions, camphor is oxidized with ring cleavage to give camphoric acid (69). Alternatively, bomeol may be used as starting material. Both enantiomers are commercially available. As oxidants nitric acid is most frequently used the best results are obtained when ammonium vanadate is added as a catalyst68. The ( + )-enantiomer was used for the preparation of monoperoxycamphoric acid, which is an isomeric mixture and difficult to separate69. The peracid has been applied with limited success as an enantioselective epoxidation reagent (Section D.4.5.2.). 

Lewis acid-promoted [3+2] cycloadditions of aziridines and epoxides proceeding via carbon-carbon bond cleavage of three-membered ring heterocycles are demonstrated for the first time. This proposal details plans for extending these initial results into a general synthetic method for the enantioselective synthesis of structurally diverse pyrrolidine- and tetrahydrofuran-containing organic compounds. Expected outcomes of the proposed work will include... 

Asymmetric epoxidation of chalcones followed by cleavage of the oxirane ring with PhCH2SH and cyclisation of the resulting dihydrochalcones constitutes an enantioselective route to cis- and trans- dihydroflavonols (Scheme 9) <97T14141>. 

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