Recent Advances in β-Lactone Chemistry

After a brief historical survey, the structure, main methods of preparation and reactivity of β-lactones are examined with emphasis on developments since 1980. The structure of β-lactones is examined through theoretical methods and molecular spectroscopy (IR and NMR). The methods of preparation are rationalized around the main reactions leading to β-lactones; [2+2] cycloaddition (between ketenes and carbonyl compounds) and lactonization via oxygen-acyl bond formation (of β-hydroxy carboxylic acids or derivatives) being the two most important ones. Finally, the reactivity of β-lactones, which has developed significantly over the last years with the better understanding of stereochemical problems, is studied. Decarboxylation (leading to olefins), Lewis acid promoted rearrangement (leading to γ-lactones), nucleophilic attack (inducing oxygen-acyl or oxygen-alkyl cleavage of the β-lactone depending on the reagents and the conditions) and reaction of β-lactone enolates towards electrophiles are more particularly studied. Information on the mechanism (when available) and the implementation in synthesis of all these methods (preparation and reactivity) are given. Thus, several natural β-lactone syntheses and many examples of the use of β-lactones as intermediates are quoted from the literature. 1. Introduction 2. History 3. Structure 3.1. Theoretical Methods 3.2. Molecular Spectroscopy 4. Preparation 4.1. Lactonization via Oxygen-Alkyl Bond Formation 4.1.1. From β-Halocarboxylic Acid Salts 4.1.2. From β,γ-Unsaturated Carboxylic Acids 4.1.3. From β-Hydroxy Carboxylic Acids 4.1.4. From Other Substrates 4.2. Lactonization via Oxygen-Acyl Bond Formation 4.2.1. From β-Hydroxy Carboxylic Acids 4.2.2. From β-Hydroxy Acid Derivatives Including Transition-Metal Complexes 4.2.3. From β-Hydroxy Lithiated Ketenes 4.3. [2+2] Cycloaddition 4.4. Miscellaneous 4.4.1. Transition-Metal Promoted Reactions 4.4.2. Deoxygenation of β-Peroxylactone 4.4.3. Others 5. Reactivity 5.1. Decarboxylation 5.2. Lewis Acid Promoted Rearrangement 5.3. Reactions with Nucleophiles 5.3.1. Grignard, Organolithium and Organocuprate Reagents 5.3.2. Group IV Organometallic Compounds 5.3.3. Group V and Group VI Nucleophiles 5.3.4. Ylides 5.4. Enolate Formation and Reaction Towards Electrophiles 5.5. Miscellaneous 5.6. The Reactivity of α-Methylene-β-lactones and β-Methylene-β-lactones 5.6.1. α-Methylene-β-lactones 5.6.2. β-Methylene-β-lactones 6. Conclusion