Spontaneous generation of chirality and chiroptical spectra of N-nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes

The crystal structures of several bicyclic N-nitrosamines indicate that they crystallize in the chiral (Sohncke) space group P212121 as conglomerates. This allows the resolution of these compounds by manual picking of the enantiomorphous crystals. The optical activity of the single crystals was confirmed by their CD spectra taken in KBr disks. The absolute configurations of the title nitrosamines were assigned by crystallographic measurements and by a comparison of their CD spectra with those of a reference compound resolved by classical methods. The observed Cotton effect signs, corresponding to the n–π∗ transition, were correlated with the helicity of the inherently chiral nitrosamine chromophore.

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(1R)-1-Methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonaneC21H25NEe 93%[α]D22=+26.2 (c 4, C6H6)Source of chirality: (+)-mandelic acidAbsolute configuration: (2S)

(1R)-N-Nitroso-1-methyl-2,4-diphenyl-3-azabicyclo-[3.3.1]nonaneC21H24N2O[α]D22=+36.5 (c 2.3, C6H6)Source of chirality: (1R)-1-methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonaneAbsolute configuration: (2S)

(1R)-N-Nitro-1-methyl-2,4-diphenyl-3-azabicyclo-[3.3.1]nonaneC21H24N2O2[α]D22=+68.6 (c 3, C6H6)Source of chirality: (1R)-N-nitroso-1-methyl-2,4-diphenyl-3-azabicyclo-[3.3.1]nonaneAbsolute configuration: (2S)