Diastereoselectivity in the Lateral Metalation and Electrophilic Quenching of Isoxazolyloxazolines

Metalation and electrophilic quenching of chiral isoxazolyloxazolinee at the C-5 position of the isoxazole gives rise to modest diastereoselectivity in most cases. In general, the 4(S)-(methoxymethyl)-5(S)-phenyl-2-oxazoline auxilliary (Meyer's reagent) produces the S absolute configuration at the C-5 isoxazole position of the major diastereomer, for priorities isoxazole > El > R > H. The enantiomerically pure isoxazolyloxazolines 3 can be obtained by preparative HPLC. The isoxazolyloxazolines 3 can be deprotected selectively to produce isoxazolecarboxaldehyde 4, and 4-isoxazolyl-1,4-dihydropyridine 5. The solid-state conformation of 5 is O-endo with respect to the ring juncture between the heterocyclic rings and sp, sp with respect to the 3,5-diester groups. The (+) enantiomer of IDHP 5 proved to be 2 orders of magnitude more effective in the displacement of ³H-labeled 1,4-dihydropyridine from Ca²⁺ channels in cardiac membranes.