The ring expansion and homologation of the biomass derivative Cyrene (6,8-dioxabicyclo[3.2.1] octan-4-one) has been developed by Lewis-acid promoted reactions with ethyl diazoacetate. Insertion into the C3–C4 bond gave a ring-expanded β-ketoester regioisomer as an equilibrating mixture of diastereomers, which was subjected to a one-pot hydrolysis and decarboxylation to give the 7,9-dioxabicyclo[4.2.1]nonan-5-one system (homocyrene). The reactivity of homocyrene was then investigated in a series of transformations known for the parent 6,8-dioxabicyclo[3.2.1] octan-4-one system, including the Baeyer–Villiger oxidation affording S-6-(hydroxymethyl)pyran2-one, which has been used for the synthesis of jasmine lactone, and another one-carbon ring expansion. The ring-expansion process for Cyrene could be used to prepare chiral C6 and C7 synthons on scale from biomass.