Esters, dienoic thermal rearrangement

Lewis acid-catalysed reactions between aldehydes and trimethylsilylketen lead to /3-lactones (29), which surprisingly resist decarboxylation or rearrangement when heated to 150 °C. In contrast, the corresponding lactones derived from a,/3-unsaturated aldehydes do undergo thermal rearrangement leading to dienoic esters. 

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