[5+1]-Annulation Strategy Based on Alkenoyl Ketene Dithioacetals and Analogues

Functionalized ketene dithioacetals are versatile intermediates in organic synthesis. The important multiple roles of the dialkylthio group make these substrates particularly useful for the synthesis of a number of important classes of substituted carbo-and heterocyclic systems, such as thiophenes, lactones, pyrroles, furans, pyridines, substituted cyclohexanones, and benzene derivatives. This account focuses on the utility of alkenoyl ketene dithioacetals, which have been found useful in the synthesis of six-membered carbo- and heterocyclic systems relying upon utilization of alkenoyl ketene dithioacetals, as the 1,5-bielectrophilic component in the [5+1] annulation with carbon, nitrogen, sulfur, and other nucleophiles. 1 Introduction 2 Synthesis of Alkenoyl Ketene Dithioacetals 2.1 Synthesis of a-Acetyl Ketene Dithioacetals 2.2 Synthesis of Alkenoyl Ketene Dithioacetals 3 [5C+1C] Annulation 3.1 Synthesis of Substituted Phenols, Cyclohexenones, and Hindered Benzophenones 3.2 Synthesis of Unsymmetrical Biaryls and p-Terphenyls 4 [5C+1N] Annulation 4.1 Synthesis of Functionalized 2,3-Dihydro-4-pyridones and Bipyridines 4.2 Synthesis of Substituted Pyridines 5 [5C+1S/Se] Annulation 6 Future Directions 7 Conclusions