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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Cycloaddition of nitrones to free and coordinated (E)-cinnamonitrile: effect of metal coordination and microwave irradiation on the selectivity of the reaction
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Cycloaddition of nitrones to free and coordinated (E)-cinnamonitrile: effect of metal coordination and microwave irradiation on the selectivity of the reaction

机译：硝酮的环加成反应生成游离和配位的（E）-肉桂腈：金属配位和微波辐射对反应选择性的影响

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摘要

[2+3] Cyloaddition of N-methylnitrone to transition metal coordinated (E)-cinnamonitrile occurs exclusively at the nitrile C ident to N bond, leading to DELTA~4-1,2,4-oxadiazoline complexes, from which the heterocyclic ligand can be released an isolated in high yield. In contrast, the reaction of the nitrone with free cinnamonitrile involves the C = C bond only, yielding a diastereomeric mixture of isoxazolidine-4-carbonitriles. Microwave irradiation enhance the reaction rates of both transformations considerably, without changing their regioselectivity with respect to the thermal reactions. The two nitrile ligands in complexes of the type [MCl_2 (cinnamonitrile)_2] (M = Pt or Pd) are significantly different in reactivity. Thus, short-time microwave irradiation allows for the selective synthesis of the mono-cycloaddition product [PtCl_2 (cinnamonitrile) (oxadiazoline)], even in the presence of an excess of nitrone. Using longer irratiation times, this complex can be further tranformed into the bis-cycloaddion product [PtCl_2(oxadiazoline)_2]. The latter compound is also produced when thermal heating is applied, however, the formation of the mono-cycloaddition product fails to be selective under thermal conditions.
机译：[2 + 3] N-甲基硝基到过渡金属配位的（E）-肉桂腈的缩合仅发生在与N键相同的腈C上，从而导致DELTA〜4-1,2,4-恶二唑啉配合物，杂环配体由此形成可以高产分离地释放。相反，硝酮与游离肉桂腈的反应仅涉及C = C键，生成异恶唑烷-4-腈的非对映异构体混合物。微波辐射可显着提高两个转化的反应速率，而不会改变它们相对于热反应的区域选择性。 [MC1_2（肉桂腈）_2]型（M = Pt或Pd）的复合物中的两个腈配体的反应性显着不同。因此，即使在过量的硝酮存在下，短时间的微波照射也允许选择性合成单环加成产物[PtCl_2（肉桂腈）（恶二唑啉）]。使用更长的照射时间，该复合物可以进一步转化为双环加成产物[PtCl_2（恶二唑啉）_2]。当施加热加热时，也会产生后一种化合物，但是，单环加成产物的形成在热条件下不能选择性地进行。

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