Asymmetric oxidative α-fluorination of 2-alkylphenylacetaldehydes with AgHF2 and ruthenium/PNNP catalysts
Asymmetric oxidative α-fluorination of 2-alkylphenylacetaldehydes with AgHF2 and ruthenium/PNNP catalysts
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DOI：
10.1016/j.jfluchem.2009.05.008
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发表时间：
2009-08-01
影响因子：
1.9
通讯作者：
Mezzetti, Antonio
中科院分区：
文献类型：
--
作者：
Althaus, Martin;Togni, Antonio;Mezzetti, Antonio
在用不同HF源进行环氧开环的尝试中，我们发现刘易斯酸性[RuCl（PNNP）]（+）（1）或[Ru（OEt 2）（2）（PNNP）]（2+）（2）催化剂促进[1，2]-苯基位移在苯基取代的环氧化物中进行Meinwald重排，得到相应的2-烷基苯乙醛，其在二氟化银（AgHF 2）（PNNP是（1 S，2S）-N，N ′-双[邻-（二苯基膦基）亚苄基]环己烷-1，2-二胺）存在下在α-位氟化。以PhCH（R）CHO（R = Me，Et，Pr-i，Bu-t）为底物的醛缩合反应的优化结果表明，催化剂[1] SbF_6具有中等程度的对映选择性（最高可达27%ee）和35%的产率。底物范围限于苯甲醛。该反应对于过渡金属催化剂来说是前所未有的。间接证据表明，该机制涉及化学氧化，然后与F-的对映选择性取代。(C)2009 Elsevier B. V.保留所有权利。
During attempts directed at epoxide ring opening with different HF sources, we discovered that the Lewis acidic [RuCl(PNNP)](+) (1) or [Ru(OEt2)(2)(PNNP)](2+) (2) catalysts promote the [1,2]-phenyl shift (Meinwald rearrangement) in phenyl-substituted epoxides to give the corresponding 2-alkylphenylacetaldehydes, which are fluorinated at the alpha-position in the presence of silver bifluoride (AgHF2) (PNNP is (1S,2S)-N,N'-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine). The optimization of aldehyde fluorination with PhCH(R)CHO (R = Me, Et, Pr-i, Bu-t) as substrates showed that catalyst [1]SbF6 gives a moderate degree of enantioselectivity (up to 27% ee) and 35% yield. The substrate scope is limited to benzylic aldehydes. The reaction is unprecedented for transition metal catalysts. Circumstantial evidence suggests that the mechanism involves chemical oxidation followed by enantioselective fluorination with F-. (C) 2009 Elsevier B.V. All rights reserved.