Synthesis of 1,4-Dicarbonyl Compounds and Cyclopentenones from Furans

Furans have proven to be useful precursors for a wide variety of cyclopentenones which are present in numerous natural products as the major structural feature. The ready availability of the starting materials and the simplicity of the procedures make them attractive candidates for the synthesis of cyclopentenones. This has given rise to a steady increase in the preparation of both 1,4-dicarbonyl compounds and of cyclopentenones from furans. In this review, we discuss the best known methods for the preparation of 1,4-dicarbonyl compounds by ring cleavage of furans, and their conversion into cyclopentenones. Then, we illustrate the exceptionally high capability of some furan derivatives, such as 2-furylcarbinols, to be directly converted into cyclopentenones by molecular rearrangement. 1. Introduction 2. Preparation of 1,4-Dicarbonyl Compounds from Furans 2.1. Acid Catalyzed Ring Opening 2.2. 1,4-Dicarbonyl Compounds via 2,5-Dialkoxy-2,5-dihydrofurans 2.3. 1,4-Dicarbonyl Compounds via Oxidative Ring Fission 2.4. 1,4-Dicarbonyl Compounds via the Marckwald Reaction 3. Cyclopentenones from Alkylfurans 3.1. Via 1,4-Dicarbonyl Compounds 3.2. Via Oxidation 3.2.1. Oxidation with Bromine and by Electrochemical Means 3.2.2. Oxidation with Hydrogen Peroxide 3.2.3. Oxidation with Chromium(VI) Reagents 4. Cyclopentenones from Furylidene Ketones 5. Cyclopentenones from Furylcarbinols 5.1. Reagents 5.2. Substrates 5.3. Byproducts 5.4. Synthesis of Isomeric Cyclopentenones 6. Other Reactions 6.1. Cyclopentenones via Carbenes 6.2. Cyclopentenones from Stenhouse Salts 7. Conclusion