Acyl Azides: Versatile Compounds in the Synthesis of Various Heterocycles

Carbon-nitrogen bond formation is one of the most important reactions in organic chemistry. Various synthetic strategies for the generation of C-N bonds are described in the literature. For example, primary amines can be easily synthesized by the thermal decomposition of an acyl azide to an isocyanate, i.e. the Curtis rearrangement, followed by hydrolysis; the Curtius rearrangement has been used extensively. Furthermore, the advantage of the Curtius rearrangement is the isolation of acyl azides as well as the corresponding isocyanates. The isocyanates can be converted into various nitrogen-containing compounds upon reaction with various nucleophiles that can be used as important synthons for cyclization, in other words, for the synthesis of heterocycles. Therefore, this review demonstrates the importance of acyl azides not only in the synthesis acyclic systems, but also in the synthesis of various nitrogen-containing heterocycles. 1 Introduction 2 Synthesis of Acyl Azides 2.1 Acyl Azides from Carboxylic Acid Derivatives 2.2 Acyl Azides by Direct Transformation of Carboxylic Acids 2.3 Acyl Azides from Aldehydes 2.4 Carbamoyl Azides from Haloarenes, Sodium Azide, and N -Formylsaccharin 3 Mechanism of Formation of Isocyanates 4 Synthesis of Diacyl Azides 5 Synthetic Applications 5.1 Synthesis of Pyrimidinone Derivatives 5.2 Dihydropyrimidinone and Isoquinolinone Derivatives 5.3 Synthesis of Tetrahydroisoquinoline Skeleton 5.4 Synthesis of Five-Membered Heterocycles 5.5 Heterocycles Synthesized Starting from Homophthalic acid 5.6 Heterocycles Synthesized from 2-(Ethoxycarbonyl)nicotinic Acid 5.7 Formation of Aza-spiro Compounds 5.8 Parham-Type Cyclization 5.9 Diazepinone Derivatives 5.10 Synthesis of Pyridine Derivatives 5.11 Synthesis of Indole Derivatives 6 Miscellaneous 7 Conclusion