STEREOCHEMISTRY OF NUCLEOPHILIC DISPLACEMENT ON 2 PHOSPHORIC MONOESTERS AND A PHOSPHOGUANIDINE - THE ROLE OF META-PHOSPHATE
STEREOCHEMISTRY OF NUCLEOPHILIC DISPLACEMENT ON 2 PHOSPHORIC MONOESTERS AND A PHOSPHOGUANIDINE - THE ROLE OF META-PHOSPHATE
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DOI：
10.1021/ja00329a047
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发表时间：
1984-01-01
影响因子：
15
通讯作者：
KNOWLES, JR
中科院分区：
文献类型：
--
作者：
BUCHWALD, SL;FRIEDMAN, JM;KNOWLES, JR
为了研究单体偏磷酸盐的作用和磷酸单酯醇解中过渡态的性质，苯基[（J？）160，170，180]磷酸酯和2，4-二硝基苯基[（。R）-160，170，180]磷酸酯的合成，并对磷酸苯酯一价阴离子和磷酸二硝基苯酯二价阴离子甲醇解的立体化学过程进行了评价。[(J?)- 160，170，180]还合成了磷酸肌酸，并测定了其甲醇分解的立体化学过程。在每种情况下，完全反转的配置在磷观察。很明显，偏磷酸盐，如果它在质子溶剂中作为这些反应中的真正中间体存在，不会离开它生成的溶剂笼。事实上，产物的形成比假定的偏磷酸盐中间体的旋转发生得更快。因此，这些位移必须通过前缔合机制发生，其中可能有一些来自引入的亲核试剂的帮助。目前的结果不允许区分“preassociative一致”路径（即，通过一个非常松散的过渡态的SN 2-样位移）和“preassociative逐步”路径通过一个偏磷酸盐中间的非常短的寿命。
For the role of monomeric metaphosphate and the nature of the transition states in the alcoholysis of phosphoric monoesters to be examined, phenyl [(J?)-160,170,180] phosphate and 2, 4-dinitrophenyl [(. R)-160,170, l80] phosphate have been synthesized and the stereochemical course of the methanolysis of phenyl phosphate monoanion and of dinitrophenyl phosphate dianion has been evaluated.[(J?)-160,170,180] Phosphocreatine has also been synthesized and thestereochemical course of the methanolysis of this molecule determined. In eachcase, complete inversion of configuration at phosphorus is observed. It is clear that metaphosphate, if it exists as a true intermediate in these reactions in protic solvent, does not leave the solvent cage in which it is generated. Indeed, product formation occurs more rapidly than rotation of the putative metaphosphate intermediate. These displacements must therefore occur by preassociative mechanisms in which there may be some assistance from the incoming nucleophile. Thepresent results do not allow a distinction to be made between a “preassociative concerted” path (that is, an SN2-like displacement via a very loose transition state) and a “preassociative stepwise” path via a metaphosphate intermediate of very short lifetime.