33856-70-1Relevant academic research and scientific papers
Phosphabarrelenes as ligands in rhodium-catalyzed hydroformylation of internal alkenes essentially free of alkene isomerization
Fuchs, Evelyn,Keller, Manfred,Breit, Bernhard
, p. 6930 - 6939 (2007/10/03)
Despite significant research efforts in the past, one of the remaining problems to be solved in industrially important hydroformylation is the chemoselective low-pressure hydroformylation of internal alkenes. We report here on a new class of phosphabarrelene/rhodium catalysts 2 that display very high activity towards hydroformylation of internal alkenes with an unusually low tendency towards alkene isomerization. Preparation of new phosphabarrelene ligands, studies of their coordination properties, as well as results obtained in the rhodium-catalyzed hydroformylation of cyclic and acyclic internal alkenes are reported.
Investigation on the regioselectivities of intramolecular oxidation of unactivated C-H bonds by dioxiranes generated in Situ
Wong, Man-Kin,Chung, Nga-Wai,He, Lan,Wang, Xue-Chao,Yan, Zheng,Tang, Yeung-Chiu,Yang, Dan
, p. 6321 - 6328 (2007/10/03)
We found that dioxiranes generated in situ from ketones 1-6 and Oxone underwent intramolecular oxidation of unactivated C-H bonds at δ sites of ketones to yield tetrahydropyrans. From the trans/cis ratio of oxidation products 1a and 2a as well as the retention of the configuration at the δ site of ketone 5, we proposed that the oxidation reaction proceeds through a concerted pathway under a spiro transition state. The intramolecular oxidation of ketone 6 showed the preference for a tertiary δ C-H bond over a secondary one. This intramolecular oxidation method can be extended to the oxidation of the tertiary γ′ C-H bond of ketones 9 and 10. For ketone 11 with two δ C-H bonds and one γ′ C-H bond linked respectively by a sp3 hydrocarbon tether and a sp2 ester tether, the oxidation took place exclusively at the δ C-H bonds. Finally, by introducing proper tethers, regioselective hydroxylation of steroid ketones 12-14 have been achieved at the C-17, C-16, C-3, and C-5 positions.
