4-Azahomoadamant-3-ene: Spectroscopic Characterization and Photoresolution of a Highly Reactive Strained Bridgehead Imine

Article abstract of DOI:10.1021/ja00289a011

Low-temperature irradiation of 1-azidoadamantane in argon, nitrogen, 3-methylpentane, or polyethylene matrices or as neat solid produced (i) the diamagnetic highly reactive strained bridgehead imine, 4-azahomoadamant-3-ene, characterized by its vibrational (Raman, IR) and electronic (UV absorption, CD) spectra, (ii) traces of 1-adamantylnitrene, detected by EPR spectroscopy and by photochemical trapping with CO, and (iii) molecular nitrogen, detected by Raman spectroscopy.A warm-up in any of the matrices produced the known dimer of the imine.In an argon matrix or in the neat solid, dimerization was observed to proceed rapidly already at about 60 K.Optical resolution of the bridgehead imine to 2percent optical purity was achieved by irradiation with circularly polarized 308-nm laser light, preferably in polyethylene between 160 and 200 K where rotational diffusion of the imine is fast and translational diffusion still slow.The activation energy for thermal racemization is believed to be at least 17 kcal/mol since no racemization was detected up to 220 K, at which temperature dimerization in the polyethylene matrix begins to be significant.Interpretation of the results is based on calculations by MNDO and INDO/S methods and suggests that the torsion angle of the severely distorted C=N moiety is 50 +/- 10 deg.