12097-36-8Relevant articles and documents
Rh(I)-bisphosphine-catalyzed asymmetric, intermolecular hydroheteroarylation of α-substituted acrylate derivatives
Filloux, Claire M.,Rovis, Tomislav
supporting information, p. 508 - 517 (2015/01/30)
Asymmetric hydroheteroarylation of alkenes represents a convenient entry to elaborated heterocyclic motifs. While chiral acids are known to mediate asymmetric addition of electron-rich heteroarenes to Michael acceptors, very few methods exploit transition metals to catalyze alkylation of heterocycles with olefins via a C-H activation, migratory insertion sequence. Herein, we describe the development of an asymmetric, intermolecular hydroheteroarylation reaction of α-substituted acrylates with benzoxazoles. The reaction provides 2-substitued benzoxazoles in moderate to excellent yields and good to excellent enantioselectivities. Notably, a series of mechanistic studies appears to contradict a pathway involving enantioselective protonation of a Rh(I)-enolate, despite the fact that such a mechanism is invoked almost unanimously in the related addition of aryl boronic acids to methacrylate derivatives. Evidence suggests instead that migratory insertion or beta-hydride elimination is enantiodetermining and that isomerization of a Rh(I)-enolate to a Rh(I)-heterobenzyl species insulates the resultant α-stereocenter from epimerization. A bulky ligand, CTH-(R)-Xylyl-P-Phos, is crucial for reactivity and enantioselectivity, as it likely discourages undesired ligation of benzoxazole substrates or intermediates to on- or off-cycle rhodium complexes and attenuates coordination-promoted product epimerization.
Ortho-chelated arylrhodium(I) complexes. X-ray structure of RhI[C6H3(CH2NMe2) 2-o,o′-C,N ](COD)
Van Der Zeijden, Adolphus A. H.,Van Koten, Gerard,Nordemann, Richard A.,Koji?-Prodi?, Biserka,Spek, Anthony L.
, p. 1957 - 1966 (2008/10/08)
The reaction of Lin[C6H3(CH2NMe 2)-o-R-o′]n with [RhCl(diene)]2 yields the ortho-chelated arylrhodium(I) complexes Rh[C6H3(CH2NMe 2)-o-R-o′](diene) (R = CH2NMe2, diene = COD (1a) or NBD (1b); diene = COD, R = Me (2) or H (3)). The solid-state structure of 1a was determined by a single-crystal X-ray diffraction study. C20H31N2Rh: triclinic, space group P1, with lattice parameters a = 10.169 (1) ?, b = 13.036 (1) ?, c = 14.688 (2) ?, α = 79.54 (1)°, β = 77.04 (1)°, γ = 79.53°; V = 1845.6 (4) ?3, Z = 4; D(calcd) = 1.448 g cm-3. Refinement with 4696 observed reflections converged at R = 0.0395. The structure of 1a consists of a rhodium(I) center that has a square-planar coordination comprising the two double bonds of COD and a C atom and one of the N atoms of the monoanionic aryl ligand. In solution compounds 1 and 2 exhibit dynamic behavior which involves a reversible dissociation of the Rh-N bond and rotation of the aryl moiety around Rh-C. This process, which generates a highly unsaturated T-shaped 14 electron species, is accompanied by the relief of steric repulsions within the complex. Complex 1 reacts with a range of electrophilic reagents leading to Rh-C bond breakage (HX, X = acac, Cl, Br, OAc, OH, OMe, L-alanyl; MXnLm, SnMe2Br2, NiBr2(PBu3)2, ZrCl4, PdCl2(NCPh)2, HgCl2, PtBr2(COD), and [IrCl(COD)]2). A redox reaction of 1 with AgX (X = OAc, NO3) leads to the formation of RhIIIX2[C6H3(CH2NMe 2)2-o,o′](H2O).
