A C20 2:3 formaldehyde-cyclohexanone adduct

The structure of the base-catalyzed condensation product of cyclohexanone and formaldehyde, (±)-(4aα,6β,9aβ,10aβ,14aβ,15aR * ,17S * )-hexadecahydro-14a,6,9a-(epoxymetheno)benzo[b]benzo[2,3]cycloocta[1,2-e]pyran-17-ol, C 20 H 30 O 3 , reported by Plesek & Munk [Collect. Czech. Chem. Commun. (1957), 22, 1596-1602; Chem. Listy (1957), 51, 633-638], is confirmed to be a 2:3 adduct of formaldehyde to cyclo-hexanone, being formed by a sequence of aldol and Michael reactions followed by intramolecular ketal and hemi-ketal formation