A simple oxime–nitrone isomerisation and intramolecular nitrone-cycloaddition reaction of 3-(alk-2-enylamino)propionaldehyde oximes

Intramolecular approach to some new D-ring-fused steroidal isoxazolidines by 1,3-dipolar cycloaddition: synthesis, theoretical and in vitro pharmacological studies

“…16 The larger size of the isopropyl group relative to the methyl group can preclude the solvent-induced side-reaction leading to the acetal 6. The 1 H NMR spectra of the crude product 5 revealed a 3 : 4 mixture of two geometric isomers, 17 which did not undergo interconversion in solution 18 and could therefore be separated by column chromatography. Theoretically, the existence of two kinds of (E) and (Z) stereostructures must be considered for 5, the computed energies of which are given in Scheme 1.…”

Intramolecular Hydro‐N‐alkylation of Hydrazones and Oxime Ethers: Synthesis of Novel D‐Secoestrone Isoquinuclidines via Domino 1,5‐Hydride Shift/Cyclization

“…Although the isomerization of intermediate 29a to nitrone 1,3-dipole 30a through an O,N-hydrogen shift is conceivable, [19] the nitrone structure is presumed to be the less stable tautomer in the equilibrium. [20] The oxyiminium ion 29a, however, did not seem to have enough electrophilic force to induce a hydride shift. Interestingly, when the oxime ethers 28b-d of 8 were subjected to similar Lewis acid treatment, formation of the corresponding 9,13-bridged products 32b-d was observed (Table 1, entries 9-11).…”

High diastereoselectivity induced by intermolecular hydrogen bonding in [3 + 2] cycloaddition reaction: experimental and computational mechanistic approaches

“…The secondary orbital interactions , noncovalent attractive interactions between the N ‐bonded aromatic rings belonging to the E‐ nitrone and the maleimide can cause the reaction to proceed via this transition state . There are large numbers of studies that support cycloaddition reactions via E ‐nitrones . However, their sandwich interaction is largely unfavorable and computational calculations reveal that exo‐Z is the more favorable transition state.…”