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 α,β‐enones. A kinetic resolution of secondary propargylic alcohols proceeded with moderate selectivity with [Rh(( R )‐BINAP)]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 α,β‐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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)