Vinyl Acetals and Related Compounds in Organic Synthesis

This review deals with typical reactions of vinyl acetals (or 1-alkenyl acetals) with a vinyl ether subunit as part of an acetal moiety, involving carboxonium ions and enol ethers as intermediates. Related N- and S- containing compounds are also considered. Rearrangements, fragmentations, addition reactions and cycloadditions are most common among these compounds. The vinyl acetal structure may be incorporated in a ring system or may be part of an acyclic chain. Common reactions as well as differences in reactivity are discussed, emphasizing the application of vinyl acetals in synthetic organic chemistry and natural product synthesis. 1. Introduction 2. Cyclic Vinyl Acetals and Related Compounds 2.1. Reactions of 1,3-Dioxoles, 4-Methylene-1,3-dioxolanes and Analogues 2.1.1. Rearrangements and Fragmentations 2.1.2. Isomerizations, Cycloadditions and Addition Reactions 2.1.3. Miscellaneous 2.2. Reactions of 4H-1,3-Dioxins and 4-Methylene-1,3-dioxanes 2.2.1. Isomerizations and Fragmentations 2.2.2. Addition Reactions 2.2.3. Miscellaneous 2.3. Reactions of 4,5-Dihydro-1,3-dioxepins 2.3.1. Rearrangements 2.3.2. Addition Reactions, Cycloadditions and Substitutions 2.3.3. Miscellaneous 3. Acyclic Vinyl Acetals 3.1. Rearrangements 3.2. Miscellaneous 4. Concluding Remarks