Theoretical analysis of competitive directions of electrocyclization of 3,4,6-triazaocta-1,3,5,7-tetraene. Investigation of the structure and electrocyclization of 1,2,4-triazahexa-1,3,5-triene

摘要

Theoretical analysis of competing directions of electrocyclization of triazatetraene H2C=CH-N=N-CH=N-CH=CH2, triazatrienes H2C=CH-N=N-CH=NH and HN=N-CH=N-CH=CH2, and 1,4-diphenyl-1,2,4-triazabuta-1,3-diene Ph-N=N-C(R)=N-Ph was carried out. Specific features of cyclization of these compounds were explained by differences in the energies of π-orbitals of C=C, C=N, and N=N bonds and in bond orders of atoms forming a new bond in the reaction. The activation barrier and the structure of the transition state of the electrocyclization of 1,2,4-triazahexa-1,3,5-triene were studied by AMI, MNDO, and MINDO/3 methods. The electrocyclization of triazatriene is an asymmetric disrotatory process. The rotation angle of the terminal CH2group around the C=C bonds is twice as large as that of the NH group around the N=N bond. The 1,3-prototropic shift in dihydro-1,2,4-triazines is discussed