Rhodium-Catalyzed Asymmetric Aqueous Pauson-Khand-Type Reaction

• Published in: Chemistry : a European journal Vol. 11; no. 13; pp. 3872 - 3880
• Main Authors: Kwong, Fuk Yee, Li, Yue Ming, Lam, Wai Har, Qiu, Liqin, Lee, Hang Wai, Yeung, Chi Hung, Chan, Kin Shing, Chan, Albert S. C.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 20-06-2005; WILEY‐VCH Verlag
• Subjects: Alkynes - chemistry; asymmetric catalysis; Catalysis; Cyclization; Heterocyclic Compounds - chemical synthesis; Models, Chemical; Molecular Structure; Pauson-Khand reactions; phosphane ligands; rhodium; Rhodium - chemistry; Water - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200401237

An interesting rhodium‐catalyzed asymmetric aqueous Pauson–Khand‐type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions. Various enynes were transformed to the corresponding bicyclic cyclopentenones in good yield and enantiomeric excess (up to 95 % ee). A study of the electronic effects of the enyne substrates revealed a correlation between the electronic properties of the substrates and the ee value obtained in the product of the Pauson–Khand‐type reaction. A linear free‐energy relationship was observed from a Hammett study.
Making rings in water: Asymmetric Pauson–Khand‐type cyclizations were accomplished with a chiral rhodium–P‐Phos complex at 100 °C in aqueous conditions (see scheme; cod=cycloocta‐1,5‐diene, Ts=toluene‐4‐sulfonyl). An interesting electronic effect was observed between the electronic properties of the substrates and the enantiomeric excess of the products in a Hammett study.