2002 multi-membered N-heterocycles

multi-membered N-heterocyclesR 0690

37 - 167Amino Acid Derived Intramolecular 1,3-Dipolar Cycloadditionsthat Form Bridged Medium Ring Systems with DiastereoselectiveControl. — Intramolecular cycloaddition of alkenyl-substituted nitrones, insitu generated from aldehydes (I) and (VIII) with N-substituted hydroxylamines(II), provides access to [4.3.0]bicyclic and [4.2.1]tricyclic adducts. The productratio depends not only on the substitution pattern but also on the presence orabsence of ZnCl2 during cyclization. Reductive cleavage of the isoxazolidinering with Zn/AcOH affords medium-sized N-heterocycles bearing variousfunctional groups. The o-nitrobenzenesulfonyl protecting group is optimal forthe presented reaction, but it has to be cleaved off prior to reductive cleavageof the N–O bond, since the nitro group is reduced, too, under the action ofZn/AcOH. The method is successfully extended to a proline-derived aldehyde[from (XI)]. — (LIU, YANBIN; MADEN, AMY; MURRAY, WILLIAM V.;Tetrahedron 58 (2002) 16, 3159-3170; Chem. Dev., R. W. Johnson Pharm. Res.Inst., Raritan, NJ 08869, USA; EN)

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2002 multi-membered N-heterocycles

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