Electronically Neutral 2-Aza-1,3-dienes: Are They Useful Intermediates in Organic Synthesis?

The reactivity and synthetic utility of electronically neutral 2-Aza-1,3-dienes, i.e. those not containing electron-withdrawing or electron-donating substituents, are shown in cycloaddition reactions for the first time. Other types of processes leading to the regioselective synthesis of several heterocyclic systems such as pyridines, azaphosphorines and diazasemibullvalene derivatives is also indicated. 1. Introduction 2. [4+2] Cycloaddition Reactions 2.1. Diels-Alder Reactions with Azodienophiles and Tetracyanoethylene 2.2. [4+2] Cycloaddition Reactions with Heterocumulenes 2.3. [4+2] Cycloaddition Reactions with Carbonyl Compounds. Synthesis of 1,3 Amino Alcohols 3. C-H_α Reactivity 3.1. Heterocyclization Reactions. Synthesis of Pyridines 3.2. Halogenation Reactions. Synthesis and Reactivity of α-Halogenated 2-aza-1,3-dienes 4. Nitrogen Atom Reactivity 4.1. Silylation Reactions 4.2. Heterocyclization Reactions. Synthesis of 1,4-Dihydro-1,4-azaphosphorine 4-Oxides 5. Conclusions