Synthesis of Seven-Membered Heterocycles via Pericyclic Reactions and Cyclic Intermediates

The synthesis of seven-membered heterocycles with up to three nitrogen, oxygen, and/or sulfur heteroatoms is described. Only monocyclic (non-annulated) rings have been considered. Pericyclic reactions play a role at one or more stages of the synthetic sequence. 1. Introduction 2. The 4 + 3 Combination 2.1. Diels-Alder Reactions 2.2. 1,3-Dipolar Cycloadditions 2.3. Miscellaneous 3. The 5 + 2 Combination 3.1. [2 + 2] Cycloadditions 3.2. [4 + 2] Cycloadditions 3.3. Miscellaneous 4. The 6 + 1 Combination 4.1. Reactions Involving the Bicyclo[2.2.0]hexene System 4.2. Insertion into Monocyclic Six-Membered Rings 4.3. Miscellaneous 5. The 7 ???? 7 Conversion 5.1. Rearrangements of Three-Membered Ring Systems 5.2. Ring Expansion via Intermediate Nitrenes and Azirines 5.3. Rearrangement of Ylides 5.4. Bicyclic Intermediates via Ionic Reactions 5.5. Ring Expansions via [1,2] Shifts 5.6. 1,7-Electrocyclization 6. Miscellaneous