The Ground State and Excited State Reactions of Enamides

The preparation and properties of enamides and dienamides are described, and their synthetically useful ground state (thermal) and excited state reactions illustrated. Photochemically, simple enamides undergo a [1,3]acyl radical shift. The dienamides undergo a 6π electron photocyclization to form heterocycles. This photocyclization reaction has been used to prepare heterocycles and natural products. Methods have been developed for the reduction of transient intermediates in the photocyclization which has led to enantioselectivity. Examples are given, especially in the formation of phenanthrenes and analogs from stilbene enamides, where other photochemical reactions can occur. The thermal chemistry of enamides and dienamides is largely due to their ability to undergo Diels-Alder [4+2]cycloaddition reactions. Intra- and intermolecular cycloadditions are described and their application to natural product synthesis illustrated. Enamides and dienamides can undergo synthetically useful oxidation, reduction, and metallation; however, these reactions have not been extensively investigated. The nucleophilic character of enamides is indicated by a number of intra- and intermolecular transformations leading to the formation of interesting heterocyclic compounds. 1. Preparation of Enamides and Dienamides 1.1. Preparation of Enamides 1.2. Preparation of Dienamides 2. Conversion of Stilbene Enamides to 5,6-Dilrydro-4H-dibenzo-[de,g]quinolines (Phenanthrene Analogs) 3.The Photochemistry of Enamides 4. Photocyclization Reactions of Dienamides 4.1. Heterocyclic Synthesis Using Dienamides 4.2. Reductive Photocyclizations of Dienamides 4.3. Thioenamide Photochemistry 4.4. Alkaloid Synthesis Using Dienamide Photocyclizations 4.4.1 Isoquinoline Derived Alkaloids 4.4.2. Indole Alkaloids 5. The Thermal Chemistry of Enamides and Dienamides 5.1. lntramolecular Cycloaddition of Dienamides 5.2. Intermolecular Cycloaddition of Enamides 5.3. Intermolecular [4+2]Cycloaddition of Dienamides 5.4. Oxidation of Enamides and Dienamides 5.5. Reduction of Enamides 5.6. Metallation of Enamides and Dienamides 5.7. Miscellaneous Reactions of Enamides and Dienamides 6. Addendum