Cationic Rhodium(I)/H8-binap Complex Catalyzed [2+2+2] Cycloadditions of 1,6-and 1,7-Diynes with Carbonyl Compounds

We have established that a cationic rhodium(I)/H-8-binap complex catalyzes [2+2+2] cycloadditions of a variety of 1,6- and 1,7-diynes with both electron-deficient and electron-rich carbonyl compounds, leading to dienones in high yield under mild reaction conditions. In the reactions with acyl phosphonates, the reactivity of 1,6- and 1,7-diynes was highly dependent on their own structures. The addition of chelating diethyl oxalate effectively promoted the [2+2+2] cycloadditions involving acyl phosphonates, presumably due to the equilibrium formation of the desired 1: 1 rhodium complex of the diyne and the acyl phosphonate by facile ligand exchange between the diyne and weakly coordinated diethyl oxalate. In the reactions involving bifunctional carbonyl compounds or unsymmetrical 1,6-diynes, high chemo- or regioselectivities were observed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)