ABSTRACT
(DiMeIHeptCl)Pd, a hyper-branched N-aryl Pd NHC catalyst, has been shown to be efficient at performing amine arylation reactions in solvent-free ("melt") conditions. The highly lipophilic environment of the alkyl chains flanking the Pd center serves as lubricant to allow the complex to navigate through the paste-like environment of these mixtures. The protocol can be used on a multi-gram scale to make a variety of aniline derivatives, including substrates containing alcohol moieties.
ABSTRACT
NaBHT (sodium 2,6-di-tert-butyl-4-methylphenolate), a strong, but hindered and lipophilic base, has been effectively paired with similarly lipophilic, high-reactivity Pd-NHC (N-heterocyclic carbene) catalysts to produce an ideal combination for performing solvent-free (melt) cross-coupling amination. The mild nucleophilicity of NaBHT, coupled with the anti-oxidant properties of its conjugate acid byproduct, BHT means the process seems to have no functional group incompatibilities. Highly effective coupling of base-sensitive and redox-active functional groups was observed in all cases with only 0.1-0.2â mol percent catalyst. Comparisons using the standard base for this reaction, KOtBu, led to poor couplings or complete degradation in most applications - only NaBHT works.
Subject(s)
Butylated Hydroxytoluene , Sodium , Amination , Catalysis , SolventsABSTRACT
The [(iPr3 P)Ni]5 H6 cluster (1) and H2 C=CHOtBu react at room temperature to form the new pentanuclear NiH carbide [(iPr3 P)Ni]5 H4 (C)(CO) (3), along with an equivalent of isobutylene. This transformation requires the activation of multiple unreactive bonds, including C-H, C-C, and C(sp3 )-O bond cleavage. Analysis of the reaction mixture by 1 Hâ NMR revealed the production of two additional paramagnetic species, assigned as [(iPr3 P)Ni]4 H4 (C-CH3 )NiOtBu (4 a) and [(iPr3 P)Ni]4 H4 (C-CH2 OtBu)NiOtBu (5 a), which arise from C(sp2 )-O bond cleavage and CH bond rearrangements. The reaction of 1 with H2 C=CHOSiMe2 CH2 Ph produced the isolableâ 4 a analogue [(iPr3 P)4 Ni5 ]H4 (CCH3 )(OSiMe2 CH2 Ph) (4 c). An isolable analogue of 5 a was obtained from the reaction of 1 with H2 C=CHOAd (Ad=1-admantyl), which produced [(iPr3 P)4 Ni5 ]H4 (CCH2 OAd)(OAd) (5 d). The utilization of both cluster faces and vertices for bonding substrate fragments in these transformations demonstrates the remarkable flexibility of the robust Ni5 H4 core in the cooperative activation of multiple C-O, C-C and C-H bonds.
ABSTRACT
The cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[7.3.1.0(2,7)]trideca-2(7),11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicarbonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product.
