Synthesis and structure of edulans I and II

Abstract

Eculans I and II have been shown by synthesis to be the epimeric 3,5,6,8a-tetrahydro-2,5,5,8a-tetramethyl-2H-1-benzopyrans (11) and (10). Diels–Alder addition of penta-1,3-diene to bromomesityl oxide, elimination of hydrogen bromide, and aldol condensation with acetaldehyde produced the hydroxy-ketone (1) already used in the synthesis of β-damascenone, reduction of which gave 1-(2,6,6-trimethylcyclohexa-1,3-dienyl)butane-1,3-diol (3). Cyclisation of this diol (3) with acid led to (±)-edulan II, isomerised to (±)-edulan I by further treatment with acid. N.m.r. spectrometry at 100 MHz, including use of double irradiation, INDOR, and lanthanide shifts, confirmed the structures of the edulans.