No abstract

The mechanism of the Rh-catalysed [2+2+2] cycloaddition reaction of diynes with monoynes has been examined using ESI-MS and ESI-CID-MS analysis. The catalytic system used consisted of the combination of a cationic rhodium(I) complex with bisphosphine ligands, which generates highly active complexes that can be detected by ESI(+) experiments. ESI-MS on-line monitoring has allowed the detection for the first time of all of the intermediates in the catalytic cycle, supporting the mechanistic proposal based mainly on theoretical calculations. For all ESI-MS experiments, the structural assignments of ions are supported by tandem mass spectrometry analyses. Computer model studies based on density functional theory (DFT) support the structural proposal made for the monoyne insertion intermediate. The collective studies provide new insight into the reactivity of cationic rhodacyclopentadienes, which should facilitate the design of related rhodium-catalysed C-C couplings.

Have a good SIP: P-stereogenic secondary iminophosphorane (SIP) ligands with a sulfonyl group attached to nitrogen have been prepared. In the presence of rhodium, the tautomeric equilibrium is shifted from the favored PH tautomer towards the P(III) tautomer, thereby allowing coordination of the SIP ligand through the P and O atoms. The resulting Rh complexes are effective in the [2+2+2] cycloaddition of enediynes with terminal alkynes.

P‐stereogene sekundäre Iminophosphorane (SIPs) mit einer Sulfonylgruppe am Stickstoffatom wurden entwickelt. In Gegenwart einer Rhodiumquelle wird das Gleichgewicht vom ansonsten bevorzugten PH‐Tautomer hin zum PIII‐Tautomer verschoben, sodass der SIP‐Ligand über das P‐ und ein O‐Atom koordinieren kann. Die resultierenden Rh‐Komplexe vermitteln die [2+2+2]‐Cycloaddition von Endiinen mit endständigen Alkinen.

A rhodium-catalyzed asymmetric synthesis of 5,5-disubstituted cyclohexa-1,3-dienes has been achieved by [2+2+2] cycloaddition reactions between diynes and Morita-Baylis-Hillman (M-B-H) adducts as unsaturated substrates. Products containing two adjacent chiral centres (quaternary and tertiary, respectively) were obtained with complete diastereoselectivity and high enantioselectivity (84-97%) through a kinetic resolution of the M-B-H adduct. Furthermore, these highly substituted cyclohexadienes reacted with dienophiles to afford the corresponding Diels-Alder cycloadducts in good yieldsFinancial support from the Spanish Ministry of Education and Science (MINECO) (Projects No.: CTQ2014-54306-P, CTQ2012-32436 and a RyC contract to A. L.) and the DIUE of the Generalitat de Catalunya (Project No.: 2014SGR931) are acknowledge