α- and β-oxygenated aldehydes derived from Diels–Alder reactions as substrates for hydroxynitrile lyases

3,4-Dihydro-2H-pyran-2-carbaldehyde (1) and 2-methoxycyclohex-3-encarbaldehyde (2) obtained by thermal or chemocatalytic Diels–Alder reactions were converted into the corresponding cyanohydrins by hydroxynitrile lyase catalysis. Modelling investigations give a clear interpretation for the steric course of the biocatalytic cyanohydrin reaction of these α- and β-oxygenated aldehydes.