The Base-Induced Fragmentation of N,N-Dibenzyl-N′-aryltriazenes

Abstract

Deprotonation of N,N-dibenzyl-N"-aryltriazenes, either in liquid phase or on solid support, by a strong base (n-BuLi or LDA) leads to fragmentation of the N-N single bond to give an imine and a diazenyl anion, which decomposes by loss of nitrogen to the parent aryl anion. The imine is deprotonated to give a 2-aza allyl anion, which is subsequently trapped by electrophiles. As an overall result, this fragmentation of the T1 triazene anchoring group represents a new traceless cleavage mode of this linker. The same mode of fragmentation was observed for the T2 linker leading to 2-aza allyl anions in liquid phase. The dibenzylamino moiety is apparently crucial since pyrrolidinodiazenylarenes can be metallated at the heterocycle without cleavage.

Key words

triazenes - diazenyl anions - azaallyl anions - umpolung - solid phase synthesis

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  The ‘Umpolung’ was referenced to the change of a a²-synthon to a d²-synthon similar to the use of N-nitrosoamines.

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7

Since the diethyl derivative is cleavable also (see below), the stability of the piperazine triazenes might be due to kinetic reasons.

9

This reaction is similar to the aza-1,2-Wittig rearrangement reaction with concurrent loss of nitrogen.

22

Bräse, S. unpublished results.

24

All new non-polymeric compounds were characterized by means of NMR, MS, IR, and elemental analysis.