Intramolecular [2+2+2] cycloaddition reactions of Yne-ene-yne and Yne-yne-ene enediynes catalysed by Rh I: Experimental and theoretical mechanistic studies

N-Tosyl-linked open-chain yne-ene-yne enediynes 1 and 2 and yne-yne-ene enediynes 3 and 4 have been satisfactorily synthesised. The [2+2+2] cycloaddition process catalysed by the Wilkinson catalyst [RhCl(PPh 3) 3] was tested with the above-mentioned substrates resulting in the production of high yields of the cycloadducts. Enediynes 1 and 2 gave standard [2+2+2] cycloaddition reactions whereas enediynes 3 and 4 suffered β-hydride elimination followed by reductive elimination of the Wilkinson catalyst to give cycloadducts, which are isomers of those that would be obtained by standard [2+2+2] cycloaddition reactions. The different reactivities of these two types of enediyne have been rationalised by density functional theory calculationsFinancial support from the Spanish MICINN (CTQ2008-05409-C02-02, CTQ2008-03077, CTQ2011-23156, CTQ2011-23121 and CTQ2009-08328) and the Catalan DIUE of the Generalitat de Catalunya (2009SGR637) is acknowledged. A. D. thanks the Spanish MEC for a doctoral fellowship. Support for the research of M. S. was received through the ICREA Academia 2009 prize for excellence in research funded by the DIU