Unexpected one-pot formation of 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and  EPR study

The unexpected formation of a highly strained polycyclic amine was found in a one-pot synthesis from cyclopentanone, dimethylfumarate and ammonium acetate. This multistep reaction includes 1,3-dipolar cycloaddition of dimethyl fumarate to the cyclic azomethine ylide formed in situ from cyclopentanone and ammonia. The polycyclic amine product was easily converted into a sterically-shielded polycyclic nitroxide. The EPR spectra and spin relaxation behavior of the nitroxide was studied in solution.  The spin relaxation seems well suited for use as a biological spin label and are comparable with those of cyclic nitroxides with two spirocyclic moieties adjacent to N-O• group.