Cationic rhodium(I)/bisphosphane complex-catalyzed isomerization of secondary propargylic alcohols to α,β-enones

We have determined that hydrogenated cationic Rh(I)/bisphosphane complexes are highly active catalysts for the isomerization of secondary propargylic alcohols to alpha,beta-enones. A kinetic resolution of secondary propargylic alcohols proceeded with moderate selectivity with [Rh((R)-BINA-P)]OTf as a catalyst. Mechanistic studies revealed that the isomerization proceeds through intramolecular 1,3- and 1,2-hydrogen migration pathways. The isomerization of propargylic diol derivatives was also investigated, which revealed that 1,4-diketones, furans, and alpha,beta-enones were obtained from 2-butyn-1,4-diol, 1-methoxy-2-butyn-4-ol, and 1-acetoxy-2-butyn-4-ol derivatives, respectively. Furthermore, chemoselectivity of the isomerization of an acetylenic diol was investigated, and preferential oxidation of a propargylic hydroxy group was observed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinhemi, Germany, 2007).