Synthesis, structure of 7-oxa-1-azabicyclo[2.2.1]heptane derivative obtained from sugar nitrone and analysis of its conformational variety

Abstract

Dispiro derivative of 7-oxa-1-azabicyclo [2.2.1]heptane 5 was synthesized as a single stereoisomer from N-(5-allyl-spiro [1,3-dioxan-2,1′-cyclohexane]-5-yl)hydroxylamine 2 and protected d-mannose 3, through intramolecular 1,3-dipolar cycloaddition of in situ formed N-(but-3-en-1-yl)nitrone 4. Structure of product 5 was attributed on the basis of NMR and X-ray analyses. In the solid state, three crystallographically independent molecules of 5 were detected, every exhibiting a different orientation of spiro connected rings. Conformational analysis performed by DFT calculations in the gas phase was performed and revealed that the conformations observed in the crystal correspond to the most stable molecular geometries. Two of them were also found to be dominant in solution.