Properties of the [4]Annulene System. Induced Paramagnetic Ring Current Sir:Recent remarkable achievements in annulene1 chemistry are, undoubtedly, the spectral characterization of [4]annulene (cyclobutadiene) (1) detained in a matrix at low temperatures2-6 and the isolation of its derivail) This term is defined by F. Sondheimer and R. Wolovsky, J. Amer.
and 3,4,5,6-tetrahydro-7-methoxy-2H-azepine ( I b ) undergo a mild exothermic reaction with aziridines (Z), yielding 1 -iminomethyl-substituted aziridines (3) ( Table I).
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