Syntheses and Reactions of 2-Alkyl-1,3-cyclopentanediones (2-Alkyl-3-hydroxy-2-cyclopenten-1-ones)

Methods for the preparation of 2-alkyl-1,3-cyclopentanediones as well as synthetically useful reactions of this class of ß-dicarbonyl compounds are reviewed. Initially, these compounds were only used as important intermediates in the total synthesis of estrone and related 19-norsteroids, but during the last two decades they have become versatile intermediates for a constantly growing number of other cyclopentanoid natural products as well. 1. Introduction 2 Syntheses of 2-Alkyl-1,3-cyclopentanediones 2.1. Condensations with Succinic Acid or Succinic Acid Derivatives 2.2. Condensation of Dialkyl Oxalates with Methyl ketones and Reduction of 2-Alkyl-1,3,4-cyclopentanetriones 2.3. Cyclization of 4-Oxoalkanoic Acids and Their Derivatives 2.4. Monoalkylation of 1,3-Cyclopentanedione 2.5. Ring Enlargement of 1,2-Bis(trimethylsiloxy)-1-cyclobutenes 2.6. Other Methods 3. Reactions of 2-Alkyl-3-hydroxy-2-cyclopenten-1-ones (2-Alkyl-1, 3-cyclopentanediones) 3.1. Reactions of Nucleophiles with the 1-Oxo Group 3.2. Reactions of Electrophiles with the 3-Hydroxy Group 3.3. Reactions of Non-carbon Electrophiles at Carbon Atom 2 3.4. Reactions of Electrophiles at Carbon Atom 4 and/or 5