SELECTIVE HALOGENATION OF STEROIDS USING ATTACHED ARYL IODIDE TEMPLATES
SELECTIVE HALOGENATION OF STEROIDS USING ATTACHED ARYL IODIDE TEMPLATES
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DOI：
10.1021/ja00445a038
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发表时间：
1977-01-01
影响因子：
15
通讯作者：
KALEYA, R
中科院分区：
文献类型：
--
作者：
BRESLOW, R;CORCORAN, RJ;KALEYA, R
在芳香族溶剂中二氯化苯碘对类固醇的自由基氯化可以是相当有选择性的，导致在未活化的叔位上官能化。该过程涉及C原子的溶剂络合物并且可以通过底物中的取代基来引导。当二氯化芳基碘试剂直接附着在底物上时，可以通过不同的机制实现更高的选择性。因此，3-胆甾烷基间碘苯甲酸酯二氯化物在自由基链过程中经历内部H提取，得到9-氯类固醇。该过程由底物和试剂之间的几何关系指导，并且其他几何形状可用于指导 C-14 或 C-17 的官能化。一种变体是自由基中继过程，其中中间氯代芳基自由基是通过 C 原子转移到附着在底物上的模板分子而产生的。在这里，也可以调整几何关系来指导反应。该过程通过可的松合成、谷甾醇和胆固醇向雄甾酮的转化以及卡烯内酯中间体的合成来说明。在一种情况下，即使在未受保护的烯酮系统存在的情况下，未活化的 C 也会发生模板定向卤化。
The free radical chlorination of steroids by phenyliodine dichloride in aromatic solvents can be rather selective, leading to functionalization at unactivated tertiary positions. This process involves solvent complex of the C. atom and can be directed by substituents in the substrate. More selectivity is achieved by a different mechanism when the aryliodine dichloride reagent is directly attached to the substrate. Thus 3 -cholestanyl m-iodobenzoate dichloride undergoes internal H abstraction in a free radical chain process to afford a 9 -chlorosteroid. The process is directed by the geometric relationship between substrate and reagent, and other geometries can be used to direct functionalization at C-14 or at C-17. A variant is the radical relay process, in which the intermediate chloroidoaryl radical is generated by C atom transfer to a template molecule attached to the substrate. Here too, geometric relationships can be adjusted to direct the reactions. The processes are illustrated by a cortisone synthesis, by the conversions of sitosterol and cholesterol to androsterone and by synthesis of a cardenolide intermediate. In 1 case the template directed halogenation of an unactivated C took place even in the presence of an unprotected enone system.