La Premiere etape de cycloaddition de la reaction croisee,quiest fortement selection vis-a-vis-a-vis de la形成 de monocycloadduits,est realisee par reactors d'un triene active avec des olenes cycliques ou celles de trienes avec des olenes acycliques Les secondes cycloadditions avec une variete de dienophiles conduisent a des bis-adduits de type croises
Sequential Acid/Base-Catalyzed Polycyclization of Tryptamine Derivatives. A Rapid Access to Büchi's Ketone
作者:Nicolas Heureux、Johan Wouters、István E. Markó
DOI:10.1021/ol0521127
日期:2005.11.1
[reaction: see text] The development of an efficient and diastereoselective methodology that allows the rapid construction of the tetracyclic core of the Aspidosperma and Strychnosalkaloid families is described. Our approach relies upon two key steps: a sequential silica gel/potassium tert-butoxide polycyclization of a tryptamine precursor and a tandem oxidative decarboxylation/ring-closing reaction
Schiff base-like ligand H2LTerPh featuring a para-terphenyl backbone was synthesized and converted in two steps to an octahedral iron(II) coordination polymer with 1,2-bis-(4-pyridyl)-ethylene as bridging ligand. Single crystal X-ray structure analysis was possible for the free ligand and the two octahedral iron(II) complexes. The Schiff base-like ligand features a [N2O2]2− coordination sphere for the
合成了具有对三联苯骨架的类席夫碱配体H 2 L TerPh并分两步将其转化为八面体铁 (II) 配位聚合物,其中 1,2-双-(4-吡啶基)-乙烯作为桥连配体。自由配体和两个八面体铁 (II) 配合物的单晶 X 射线结构分析是可能的。席夫碱样配体的金属中心具有 [ N 2 O 2 ] 2-配位球,对三联苯骨架引入了内在空间约束。用N 4 O 2表征配位聚合物通过磁性测量 (SQUID) 和室温穆斯堡尔光谱分析铁中心周围的配位球,揭示了研究的整个温度范围内的 H2S 特征。使用 DFT 计算的结构建模支持这些发现,但也支持解决方案中自旋交叉的可能性。
DIENE-TRANSMISSIVE DIELS–ALDER REACTION OF A NEW CROSS-CONJUGATED TRIENE: SELECTIVE FORMATION OF MONO- AND BIS-CYCLOADDUCT
A new activated cross-conjugated triene, 3-(methoxymethylene)-2,4-bis(trimethylsilyloxy)-1,4-pentadiene, was prepared. Its reactions with acetylenic dienophiles resulted in the exclusive formation of mono-cycloadducts, while in the reactions with cyclic olefinic dienophiles such as maleimides and maleic anhydride the mono- and bis-adducts were obtained depending upon the amounts of dienophiles.
The formal insertion of dimethoxycarbene (1a) into the acidic
C–H bond of pentane-2,4-dione (9a), methyl acetoacetate (9b),
3-methylpentane-2,4-dione (9c) and 1,3-diphenylpropane-1,3-dione (9d) is
reported as well as the insertion of 3-benzoyloxazolidin-2-ylidene (1b)
into 9c. The β-dicarbonyl compounds 9 are known to be
equilibrated with their corresponding enols in benzene solution and the
insertions appear to proceed by proton abstraction from the enol
tautomers of 9 to generate enolate anions and either a dimethoxymethyl
cation (from 1a) or a 3-benzoyloxazolidin-2-ium cation (from 1b).
Collapse of these ion pairs at the carbon atom of the enolate yields the
major product. Formal insertion of 1a into the O–H bond of the
enol tautomer of anthrone (12) is also reported.
A novel tandem transetherification—intramolecular hetero Diels–Alder reactions for construction of fused heterocycles
作者:Eiji Wada、Govindaraj Kumaran、Shuji Kanemasa
DOI:10.1016/s0040-4039(99)02003-1
日期:2000.1
β-Alkoxy-substituted α,β-unsaturated carbonyl compounds activated with an additional electron-withdrawing substituent undergo a facile tandem transetherification/intramolecular hetero Diels–Alder reactions when reacted with δ,ε-unsaturated alcohols under thermal conditions. These reactions are stereoselective producing the corresponding functionalized hydropyranopyran derivatives in good yields.