نتایج جستجو برای: cycloadditions
تعداد نتایج: 1035 فیلتر نتایج به سال:
Highly efficient catalytic asymmetric [3 + 2] cycloadditions using a chiral copper amide are reported. Compared with the chiral CuOTf/Et3N system, the CuHMDS system showed higher reactivity, and the desired reactions proceeded in high yields and high selectivities with catalyst loadings as low as 0.01 mol %.
A number of non-canonical amino acids (NCAAs) with unstrained olefins are genetically encoded using mutant pyrrolysyl-tRNA synthetase-tRNA(Pyl)(CUA) pairs. These NCAAs readily undergo inverse electron-demand Diels-Alder cycloadditions with tetrazine dyes, leading to selective labeling of proteins bearing these NCAAs in live cells.
Activation of bis-o-phenylene tetrasulfide to render it a practical benzodithiete equivalent for [4+2] cycloadditions with alkenes has been achieved with catalytic amounts of Mo(tfd)(2)(bdt) (tfd = S(2)C(2)(CF(3))(2); bdt = S(2)C(6)H(4)). Substituted 2,3-dihydro-1,4-benzodithiins are produced.
A metal-free domino [3 + 2] cycloaddition is reported to construct naphtho[2,3-d][1,2,3]triazole-4,9-dione derivatives and provide an alternative approach to the azide-alkyne cycloadditions. The key features are easily available starting materials, mild reaction conditions, a good atom economy, eco-friendly characteristics and a broad substrate scope with high yields.
A series of fused tetracycles with a benzene or cyclohexadiene core (2a-h) is satisfactorily prepared by intramolecular [2 + 2 + 2] cycloadditions of triynic and enediynic macrocycles (1a-h) under RhCl(PPh3)3 catalysis; the enantioselective cycloaddition of macrocycles 1b and 1e and gives chiral tetracycles with moderate enantiomeric excess.
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