Synthesis of Spirofluorenyl-1,2,4-oxadiazinan-5-ones through Metal-Free [3+3] Cycloaddition of N-Vinyl Fluorenone Nitrones with Aza-oxyallyl Cations

Abstract

Spirofluorenyl-1,2,4-oxadiazinan-5-ones are prepared in good to excellent yields through metal-free [3+3] cycloaddition of N-vinyl fluorenone nitrones and aza-oxyallyl cations under mild reaction conditions. Detailed studies reveal that N-vinyl fluorenone nitrones show greater reactivity in [3+3] cycloadditions with aza-oxyallyl cations compared to N-alkyl/aryl fluorenone nitrones. The spirofluorenyl-1,2,4-oxadiazinan-5-ones are easily prepared on gram scale. The present method features mild reaction conditions, broad substrate scope, good functional group tolerance and efficient [3+3] cycloadditions of 9-fluorenone nitrones.

Aza‐oxyallyl Cations and Their Applications in (3+m) Cycloaddition Reactions

“…The [3+3]‐cycloaddition reaction of aza‐oxyallyl cations with N‐vinyl fluorenone nitrones 79 led to formation of biological active spiro‐1,2,4‐oxadiazinan‐5‐one 80 with excellent yields at optimal conditions i. e., K 2 CO 3 as the base in CH 3 CN at room temperature(Scheme 22). [42a] The well‐established solvent (HFIP) for aza‐oxyallyl cations stabilization afforded trace amount of desired product. The reaction showed broad substrate scope and variety of functional group tolerance such as linear, di‐or monosubstituted 80 a – b and cyclic vinyl groups 80 c at N‐atom of fluorenone nitrones, α‐monoalkyl/aryl substituted halohydroxamates 80 d – e , different alkoxy, allyloxy, alkynyloxy groups at N‐atom of α‐haloamides, furnishing moderate to excellent yields.…”

Non-catalytic regioselective synthesis of trans bis-pyrrolo isoxazole cycloadducts in water

“…29,30 Aside from a vast range of ve membered heterocycles created using nitrone cycloaddition, there are fewer reports on the synthesis of polymeric compounds utilizing nitrones via this approach. [31][32][33] Furthermore, only a few studies report the synthesis of bis-nitrones and their usage as a dipole substrate to synthesize macro sized molecules. The use of nitrones in polymer synthesis dates back to 1971, when Manecke et al 34 for the rst time reported the synthesis of a-(p-maleinimidophenyl)-N-(phenylnitrone) that was subjected to dipolar cycloaddition with the maleinimido group in the same molecule and this upon repeated addition led to the formation of macromolecules.…”

A Role for Isatin Azomethine Imines as a Dipolarophile in Cycloaddition Reactions

“…The reason why the reaction between 1 and 2 did not undergo a [3 + 3] cycloaddition process like other 1,3-dipoles and azaoxyallyl cation , may be due to steric effects or the electronic nature of substrate 1 . Initially, we reasoned that the steric repulsion between the carbonyl groups of oxindole moiety and N-substituents of 2 disables the formation of [3 + 3] cyclcoadduct as shown in Scheme .…”