rel-(2R,4R,6S)-2-(1'-hexynyl)-4,6-dimethyl-1,3-dioxane | 137626-23-4

• 分子结构分类: 有机化合物 - 有机杂环化合物 - 二恶烷
• 英文名称: rel-(2R,4R,6S)-2-(1'-hexynyl)-4,6-dimethyl-1,3-dioxane
• CAS: 137626-23-4
• 化学式: C₁₂H₂₀O₂
• 分子量: 196.29
• InChiKey: QJJKSCNCZBVNDU-GDNZZTSVSA-N

计算性质

• 辛醇/水分配系数(LogP)：
  2.72
• 重原子数：
  14.0
• 可旋转键数：
  2.0
• 环数：
  1.0
• sp3杂化的碳原子比例：
  0.83
• 拓扑面积：
  18.46
• 氢给体数：
  0.0
• 氢受体数：
  2.0

反应信息

• 作为反应物：
  描述：

  rel-(2R,4R,6S)-2-(1'-hexynyl)-4,6-dimethyl-1,3-dioxane 在 palladium on activated charcoal 氢气 作用下， 以 正己烷 为溶剂， 反应 0.25h， 以97%的产率得到rel-(2R,4R,6S)-2-n-hexyl-4,6-dimethyl-1,3-dioxane
  参考文献：
  名称：

  Studies on the mechanism and origin of stereoselective opening of chiral dioxane acetals

  摘要：

  A systematic examination of the mechanism and origin of stereoselection in the reaction of dioxane acetals with allyltrimethylsilane was undertaken. Experimental tests for two limiting mechanisms, synchronous (S(N)2-like) and dissociative (S(N)1-like) substitution processes, were investigated. The meso 2,4,6-trisubstituted 1,3-dioxane acetals cis- and trans-1 provided an interesting opportunity to test the timing of bond breaking and making in the substitution reaction. The modest and C(2)-substituent-dependent selectivity excluded the possibility of a direct S(N)2-type attack on a complexed acetal. Further, the enol ethers 3 and 5 and acyclic acetal 7 were studied as precursors of the putative oxocarbenium ion intermediate in the dissociative limit. The weak and inverted selectivity observed with these substrates ruled out the intermediacy of the extended, separated ion in reactions of the cyclic acetals under similar conditions. A unified mechanistic scheme involving three distinct ion pairs is proposed to explain the dependence of allylation selectivity on structural and experimental variables. The three species are analogous to those proposed in the classic Winstein scheme: (1) an intimate ion pair, (2) an external ion pair, and (3) a separated ion. Each of these proposed intermediates has a different stereochemical profile and the ultimate outcome is a composite of those factors that balance the contribution of the different intermediates. The influence of C(2) substituent, acetal configuration, Lewis acid type and stoichiometry, allylsilane stoichiometry, concentration, solvent, and temperature were investigated and integrated in the proposed mechanistic scheme.

  DOI：

  10.1021/ja00021a040
• 作为产物：
  描述：

  (2s*,4R*,6S*)-4,6-dimethyl-2-phenyl-1,3-dioxane 在 palladium on activated charcoal 硫酸 、 氢气 、 对甲苯磺酸 作用下， 以 甲醇 、 苯 为溶剂， 反应 10.5h， 生成 rel-(2R,4R,6S)-2-(1'-hexynyl)-4,6-dimethyl-1,3-dioxane
  参考文献：
  名称：

  Studies on the mechanism and origin of stereoselective opening of chiral dioxane acetals

  摘要：

  A systematic examination of the mechanism and origin of stereoselection in the reaction of dioxane acetals with allyltrimethylsilane was undertaken. Experimental tests for two limiting mechanisms, synchronous (S(N)2-like) and dissociative (S(N)1-like) substitution processes, were investigated. The meso 2,4,6-trisubstituted 1,3-dioxane acetals cis- and trans-1 provided an interesting opportunity to test the timing of bond breaking and making in the substitution reaction. The modest and C(2)-substituent-dependent selectivity excluded the possibility of a direct S(N)2-type attack on a complexed acetal. Further, the enol ethers 3 and 5 and acyclic acetal 7 were studied as precursors of the putative oxocarbenium ion intermediate in the dissociative limit. The weak and inverted selectivity observed with these substrates ruled out the intermediacy of the extended, separated ion in reactions of the cyclic acetals under similar conditions. A unified mechanistic scheme involving three distinct ion pairs is proposed to explain the dependence of allylation selectivity on structural and experimental variables. The three species are analogous to those proposed in the classic Winstein scheme: (1) an intimate ion pair, (2) an external ion pair, and (3) a separated ion. Each of these proposed intermediates has a different stereochemical profile and the ultimate outcome is a composite of those factors that balance the contribution of the different intermediates. The influence of C(2) substituent, acetal configuration, Lewis acid type and stoichiometry, allylsilane stoichiometry, concentration, solvent, and temperature were investigated and integrated in the proposed mechanistic scheme.

  DOI：

  10.1021/ja00021a040

文献信息

• Studies on the mechanism and origin of stereoselective opening of chiral dioxane acetals
  作者：Scott E. Denmark、Neil G. Almstead

  DOI：10.1021/ja00021a040

  日期：1991.10

  A systematic examination of the mechanism and origin of stereoselection in the reaction of dioxane acetals with allyltrimethylsilane was undertaken. Experimental tests for two limiting mechanisms, synchronous (S(N)2-like) and dissociative (S(N)1-like) substitution processes, were investigated. The meso 2,4,6-trisubstituted 1,3-dioxane acetals cis- and trans-1 provided an interesting opportunity to test the timing of bond breaking and making in the substitution reaction. The modest and C(2)-substituent-dependent selectivity excluded the possibility of a direct S(N)2-type attack on a complexed acetal. Further, the enol ethers 3 and 5 and acyclic acetal 7 were studied as precursors of the putative oxocarbenium ion intermediate in the dissociative limit. The weak and inverted selectivity observed with these substrates ruled out the intermediacy of the extended, separated ion in reactions of the cyclic acetals under similar conditions. A unified mechanistic scheme involving three distinct ion pairs is proposed to explain the dependence of allylation selectivity on structural and experimental variables. The three species are analogous to those proposed in the classic Winstein scheme: (1) an intimate ion pair, (2) an external ion pair, and (3) a separated ion. Each of these proposed intermediates has a different stereochemical profile and the ultimate outcome is a composite of those factors that balance the contribution of the different intermediates. The influence of C(2) substituent, acetal configuration, Lewis acid type and stoichiometry, allylsilane stoichiometry, concentration, solvent, and temperature were investigated and integrated in the proposed mechanistic scheme.