Palladium(0)-catalyzed reaction of .alpha.,.beta.-epoxy ketones leading to .beta.-diketones

A Ratiometric Fluorescent Probe for Biological Signaling Molecule H2S: Fast Response and High Selectivity

“…Noyori and co‐workers reported that the isomerizations of α,β‐epoxy ketones in the presence of Pd(PPh 3 ) 4 are very sluggish even at 140 °C, but are strongly improved through the addition of bidentate phosphane ligands, especially dppe, leading to β‐diketones [Equations (32) and (33)] 56,57. The procedure has been used for the efficient isomerization of 2,6,6‐trimethyl‐1‐oxo‐2,3‐epoxycyclohexane58 and 4‐ tert ‐butyldimethylsilyloxy‐1‐oxo‐2,3‐epoxycyclopentane,59 but was ineffective with methyl 1‐ethyl‐2‐oxo‐3,4‐epoxycyclohexane‐1‐propanoate as the substrate 60.…”

Pd‐Mediated Reactions of Epoxides

“…[56,57] The procedure has been used for the efficient isomerization of 2,6,6-trimethyl-1-oxo-2,3-epoxycyclohexane [58] and 4-tert-butyldimethylsilyloxy-1-oxo-2,3-epoxycyclopentane, [59] but was ineffective with methyl 1-ethyl-2-oxo-3,4-epoxycyclohexane-1-propanoate as the substrate. [60] With a tridentate ligand such as Triphos, the isomerization is accompanied by some deoxygenation [Equation (34)].…”

Reactivity versus Stability of Oxiranes under Palladium‐Catalyzed Reductive Conditions

“…Noyori et al previously envisaged an intermediate similar to 11A for the rearrangement, catalyzed by soluble Pd 0 complexes, of α,β-epoxy ketones into β-diketones; these authors suggested that such an intermediate is formed by back-side displacement of the oxirane (Scheme 13, path a) (either in a classical nucleophilic manner or by an electron-transfer process) or from front-side oxidative addition leading to a palladaoxetane, followed by heterolytic rupture of the O-Pd bond (Scheme 13, path b). [119] As 11A could be in equilibrium with the corresponding O-palladium enolate and η 3 -oxoallyl palladium complexes, [120] the distinction between these two possible pathways is not straightforward, even from substrates with a quaternary C α or optical activity.…”