Novel diastereoisomers of C21H20O3 obtained from the cathodic reduction of methyl (2E)-3-[2-(2-{2-[(1E)-3-methoxy-3-oxoprop-1-en-1-yl]phenyl}ethyl)phenyl]prop-2-enoate

The diastereoisomeric title compounds, 5 and 6, were obtained as a result of intramolecular electrohydrocyclisation of methyl (2E)-3-[2- (2-{2-[(1E)-3-methoxy-3-oxoprop-1-en-1-yl]phenyl}ethyl)phenyl]prop-2-enoate. The common feature of the molecular structures is the presence of a central, eight-membered, –C(H)–C(H)–C C–(CH2)2–C C, ring appended to a cyclopentenyl and two phenyl rings. This study represents an unprecedented structural characterisation of such an atomic/bonding arrangement. The distinctive feature of the structures relates to the conformation of the central rings, i.e. approximating a boat in 5 and a chair in 6. This difference in molecular conformations arises from the different configurations at the methine-C atoms of the cyclopentenyl ring, i.e. R- and S-(or S- and R-) in 5 as opposed to R- and R- (or S- and S-) in 6. In each case, the hydroxyl-OH forms an intramolecular hydrogen-bond to the adjacent carbonyl-O atom so the molecular packing in each of 5 and 6 is sustained by non-conventional interactions. A three-dimensional architecture in 5 arises from a combination of phenyl-C–H…O(carbonyl) and methyl- and methylene-C–H…p contacts. In the crystal of 6, supramolecular chains with a zig-zag topology along the c-axis are formed via methyl-C–H…O(hydroxyl); the chains pack with no directional interactions between them.