Regio- and stereoselective (3 + 2)-cycloaddition reactions of nitrones with cyclic allenes

An effective approach to access functionalized 2H-cyclonona(deca)[d]isoxazoles and 15-oxo-3,10-methanobenzo[b][1]azacyclododecines has been developed by the reaction of N-aryl-C,C-bis(methoxycarbonyl)nitrones with cyclonona(deca)-1,2-dienes in a one-pot fashion. The reaction of N-aryl-C-(phenylcarbamoyl)nitrones with these allenes proceeds strictly regioselectively giving the mixtures of diastereomeric isoxazolidines containing a double bond at the C⁴-position of the isoxazolidine ring. The quantum chemical calculations show that the regioselectivity of these reactions is in good agreement with the reactivity indices of the considered compounds.

Investigating the regio-, stereo-, and enantio-selectivities of the 1,3-dipolar cycloaddition reaction of C-cyclopropyl-N-phenylnitrone derivatives and benzylidenecyclopropane derivatives: A DFT study

The biomedical importance of spirocyclopropane isoxazolidine derivatives is widely known. The 1,3-dipolar cycloaddition (1,3-DC) of C-cyclopropyl-N-phenylnitrone derivative and benzylidenecyclopropane derivatives leading to the formation of 5- and 4-spirocyclopropane isoxazolidines derivatives have been studied using density functional theory (DFT) at M06-2X/6-311G (d,p) level of theory. An extensive exploration of the potential energy surface shows that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism. While electron-donating groups (EDGs) on the benzylidenecyclopropane favor the formation of the 4-spirocyclopropane isomer, electron-withdrawing groups (EWGs) favor the reaction channels that furnish the 5-spirocyclopropane isoxazolidine isomer. Both EWDs and EDGs on the 1,3-dipole favor the formation of the 5-spirocyclopropane isoxazolidine isomer. Irrespective of the electronic nature of substituents on the C-cyclopropyl-N-phenylnitrone, the reaction channels that regioselectively lead to the formation of the 5-spirocyclopropane isoxazolidine isomer are favored. In all reactions considered, the channels that selectively lead to the formation of the cis-diastereoisomers proceed with lower activation barriers than the trans-diastereoisomers. In all cases, the observed selectivities in the title reaction are kinetically controlled.