Abstract
This review summarizes results of literature reports concerning tandem in situ generation and 1,5-electrocyclization of N-hetaryl nitrilimines reported by us and other research groups from 1960 to mid 2009. It outlines the utility of such reactions as facile synthetic strategy for synthesis of annulated triazoles and their acyclo C-nucleosides.
Highlights
A nitrilimine 1 is a flexible system of three atoms over which four pi-electrons are distributed
One can write seven possible resonance structures for such a system, the 1,3-dipolar sextet structure 1A with its complementary nucleophilic and electrophilic centers will be used throughout this article, theoretical calculations have indicated that all the octet zwitterionic structure 1B is the most stable contributor to the resonance hybrid
The product is formed via in situ 1,5-electrocyclization of the initially formed nitrilimines, whereas the product resulted from thermally induced Dimroth like rearrangement of 41.91 Treatment of each of 41 and 42 with sodium methoxide in methanol resulted in deprotection of the sugar residue and the formation of C-nucleoside 41b and 42b respectively
Summary
A nitrilimine 1 is a flexible system of three atoms over which four pi-electrons are distributed. 4. Base induced elimination of hydrogen halide from hydrazonoyl halides.. Base induced elimination of hydrogen halide from hydrazonoyl halides.23-28 The mechanism of this 1,3-elimination reaction has been studied.. Nitrilimines having a double bond at the N-terminus are prone towards the 1,5electrocyclization as depicted in equation 1. If the double bond is a part of the heterocyclic moiety, such 1,5-electrocyclization will lead to fused ring system as shown in equation 2. Nitrilimines having both α,β- and γ,δ-double bonds are susceptible to 1,7-electrocyclization of the 8-pi electron system to give the respective triazepine, oxadiazepine or thiadiazepine derivatives according to the nature of Z as shown in equation 3
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