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首页> 外文期刊>Journal of Physical Organic Chemistry >Reactions of nitrogen nucleophiles with enantiopure cyclohexenyl electrophiles: a stereo- and regio- selective study
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Reactions of nitrogen nucleophiles with enantiopure cyclohexenyl electrophiles: a stereo- and regio- selective study

机译：氮亲核试剂与对映体纯环己烯基亲电试剂的反应：立体和区域选择性研究

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The reactions of enantiopure cyclohexene epoxides and trans-1,2-bromoacetates, derived from the corresponding substituted benzene cis-dihydrodiol metabolites, with nitrogen nucleophiles, were examined and possible mechanisms proposed. An initial objective was the synthesis of new 1,2-aminoalcohol enantiomers as potential chiral ligands and synthetic scaffolds for library generation. These apparently simple substitution reactions proved to be more complex than initially anticipated and were found to involve a combination of different reaction mechanisms. Allylic trans-1,2-azidohydrins were prepared by Lewis acid-catalysed ring-opening of cyclic vinyl epoxides with sodium azide via an S_N2 mechanism. On heating, these trans-1,2-azidohydrins isomerized to the corresponding trans-1,4-azidohydrins via a suprafacial allyl azide [3,3]-sigmatropic rearrangement mechanism. Conversion of a 1,2-azidohydrin to a 1,2-azidoacetate moved the equilibrium position in favour of the 1,4-substitution product. Allylic trans-1,2-bromoacetates reacted with sodium azide at room temperature to give C-2 and C-4 substituted products. A clean inversion of configuration at C-2 was found, as expected, from a concerted S_N2-pathway. However, substitution at C-4 was not stereoselective and resulted in mixtures of 1,4-cis and 1,4-trans products. This observation can be rationalized in terms of competitive S_N2 and S_N2′ reactions allied to a [3,3]-sigmatropic rearrangement. cis-1,2-Azidohydrins and cis-1,2-azidoacetates were much more prone to rearrange than the corresponding trans-isomers. Reaction of the softer tosamide nucleophile with trans-1,2-bromoacetates resulted, predominantly, in C-4 substitution via a syn-S_N2′ mechanism. One application of the reaction of secondary amines with allylic cyclohexene epoxides, to give trans-1,2-aminoalcohols, is in the synthesis of the anticholinergic drug vesamicol, via an S_N2 mechanism.
机译：考察了对映体纯的环己烯环氧化物和由相应的取代苯顺式-二氢二醇代谢物衍生的反式1,2-溴乙酸酯与氮亲核试剂的反应，并提出了可能的机理。最初的目标是合成新的1,2-氨基醇对映异构体，作为潜在的手性配体和合成支架，以产生文库。这些看似简单的取代反应比最初预期的要复杂得多，并且发现它们涉及不同反应机理的组合。烯丙基反式1,2-叠氮基醇是通过路易斯酸通过叠氮化钠通过环S_N2机理催化环状乙烯基环氧化物的开环制备的。在加热时，这些反式1,2-叠氮基醇经由表面烯丙基叠氮化物[3,3]-σ重排机制异构化为相应的反式1,4-叠氮基醇。 1，2-叠氮醇向1，2-叠氮乙酸酯的转化使平衡位置有利于1，4-取代产物。在室温下，烯丙基反式1,2-溴乙酸酯与叠氮化钠反应，得到C-2和C-4取代的产物。正如预期的那样，从协调一致的S_N2-路径中发现C-2处的配置完全反转。然而，在C-4处的取代不是立体选择性的，并且导致1，4-顺式和1，4-反式产物的混合物。可以根据与[3,3]-σ重排相关的竞争性S_N2和S_N2'反应来合理化此观察结果。顺式1,2-叠氮基醇和顺式1,2-叠氮基乙酸酯比相应的反式异构体更容易重排。较软的甲苯磺酰胺亲核试剂与反式1,2-溴乙酸酯的反应主要通过syn-S_N2'机制引起C-4取代。仲胺与烯丙基环己烯环氧化合物反应生成反式1,2-氨基醇的一种应用是通过S_N2机理合成抗胆碱能药物vesamicol。

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