FACILE HYDRODEHALOGENATION WITH H-2 AND PD/C CATALYST UNDER MULTIPHASE CONDITIONS .3. SELECTIVE REMOVAL OF HALOGEN FROM FUNCTIONALIZED ARYL KETONES .4. ARYL HALIDE-PROMOTED REDUCTION OF BENZYL ALCOHOLS TO ALKANES
FACILE HYDRODEHALOGENATION WITH H-2 AND PD/C CATALYST UNDER MULTIPHASE CONDITIONS .3. SELECTIVE REMOVAL OF HALOGEN FROM FUNCTIONALIZED ARYL KETONES .4. ARYL HALIDE-PROMOTED REDUCTION OF BENZYL ALCOHOLS TO ALKANES
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DOI：
10.1021/jo00113a024
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发表时间：
1995-04-21
影响因子：
3.6
通讯作者：
TUNDO, P
中科院分区：
文献类型：
--
作者：
MARQUES, CA;SELVA, M;TUNDO, P
在两相系统[非极性有机溶剂和50% KOH(aq)]中在50℃下操作，在大气压下使用5% Pd/C和Hz，考虑了卤化芳香酮和苯甲醇的还原。对于酮，反应受到鎓盐存在的强烈影响，而对于醇，只有添加芳香族卤化物作为促进剂，才会发生还原反应。特别是，在 Aliquat 336（甲基三辛氯化铵）存在下，卤代酮被选择性脱卤：例如，在异辛烷溶剂中，4-氯苯丙酮、4-溴苯乙酮和 4,4'-二氯二苯甲酮生成相应的酮，选择性大于或等于 95%。没有观察到羰基的还原。如果不使用鎓盐，则烷基苯是在经典条件下在乙醇溶液中通过 Pd/C 进行还原时发生的唯一产物。同样，将伯、仲和叔苄醇还原为其相应的烃明确需要芳香族卤化物的存在；后者同时加氢脱卤生成相应的烃（例如，邻二氯苯生成苯）。在不存在卤化物促进剂的情况下，仅当醇的芳环中存在卤素时，即，如果卤代芳基醇是起始试剂，反应才会发生。在这种情况下，卤素很快就会从基材上去除，从而相应的芳香烃成为唯一的最终产品。
Operating in a two-phase system [apolar organic solvent and 50% KOH(aq)] at 50 degrees C, using 5% Pd/C and Hz at atmospheric pressure, the reduction of halogenated aromatic ketones and benzylic alcohols is considered. In the case of the ketones, the reaction is strongly influenced by the presence of an onium salt, while for the alcohols, the reduction occurs only if an aromatic halide is added as a promoter. In particular, in the presence of Aliquat 336 (methyltricaprylammonium chloride), halogenated ketones are selectively dehalogenated: for instance, in isooctane solvent, 4-chloropropiophenone, 4-bromoacetophenone, and 4,4'-dichlorobenzophenone give the corresponding ketones with selectivity greater than or equal to 95%. No reduction of the carbonyl group is observed. If no onium salt is used, alkylbenzenes are the sole products as occurs when the reduction is carried out over Pd/C in an ethanolic solution under classical conditions, Likewise, the reduction of primary, secondary, and tertiary benzylic alcohols to their corresponding hydrocarbons expressly requires the presence of aromatic halides; these latter undergo a simultaneous hydrodehalogenation to the respective hydrocarbon (for example, o-dichlorobenzene to benzene). In the absence of the halide promoter, the reaction takes place only if a halogen is present in the aromatic ring of the alcohol: that is, if haloaryl alcohols are the starting reagents. In this case the halogen is quickly removed from the substrate, so that the corresponding aromatic hydrocarbons are the sole final products.