ZWITTERIONS AS INTERMEDIATES OF THE 1,3-DIPOLAR CYCLOADDITION OF ELECTROPHILIC AZIDES TO 5-ALKYLIDENEDIHYDROTETRAZOLES - THE OTHER NON-CONCERTED LIMITING CASE

The isolable zwitterions 2 and the tetrahydrotetrazines 3 are formed in the 1,3 ‐dipolar cycloadditions of R3N3 to 1. It has been established X‐ray crystallo‐graphically that a strong steric hindrance is responsible for ring closure between the very close centers of opposite charge being difficult in 2 (R1 = H, R2 = tBu = Mes). A detailed investigation of the reactions clearly confirms that the zwitterions 2 are actually the intermediates of a non‐concerted cycloaddition (R1 = H. Me; R2 = Me, tBu; R3 = (NO2)3C6H2, p‐Tos, Mes). (Figure Presented.) Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany