Zinc mediated ring size tuned C=C reduction and C-C coupling of alpha,alpha '-(E,E)-bis(benzylidene)cycloalkanones

Reduction of substituted alpha,alpha'-(E,E)-bis(benzylidene)cycloalkanones bearing five- and six-membered rings using zinc-amalgam in glacial acetic acid yielded C=C bond reduced products and C-C coupled compounds with the carbonyl functions remaining unaffected. Ring conformation exerted pronounced influence on the extent of reduction. The diastereomerism around the coupled benzylic carbons and the relative orientations of the like groups varied with the central cycloalkanone ring types. DFT studies indicated conformational differences between the substrates of two cyclic systems and consequently the ease of electron transfer from metal to them would vary. Dimeric molecules exhibited their associative properties involving pi-pi interactions and intermolecular H-bond formation.