Hyperconjugative Effects of Allylic Substituents Are Not Important in Osmylations.
Hyperconjugative Effects of Allylic Substituents Are Not Important in Osmylations.
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烯丙基取代基的超共轭效应在锇基化中并不重要。
DOI：
10.1002/chin.198626133
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发表时间：
1986
期刊：
影响因子：
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通讯作者：
C. Mcclure
中科院分区：
文献类型：
--
作者：
E. Vedejs;C. Mcclure
然而，1应该在Z烯烃（R=烷基）中不稳定，并且对于E异构体（R= H），预期产物I的更高选择性。这与Kishi的研究结果相反。如果相互作用是重要的，则可以通过比较具有大体积供体（X= PhMe_2Si）和大体积受体（X= RS_（02））取代基的底物的锇化反应来检验。5 E和Z硅烷都应通过类似于3的几何结构反应，因为最佳供体也是最大的取代基。6对于Z硅烷（表I，条目1）观察到适当的I型面选择性，但是E硅烷反应具有产物II的选择性！7在砜的情况下，几何构型2应该是最好的，供体CH 3“反”和大体积受体（X= RS 02）在“外部”位置。对于E砜（条目4和6）观察到对II的适当选择性，但Z异构体再次显示I型选择性。很难相信高度拥挤的1应该有利于Z砜，而不管电子效应如何。因此，两种烯烃异构体之一（5）E硅烷的制备：PhSiMe 2Li+（E）烯丙基氯（THE），51%，9：1 E/Z。Z硅烷：CH 3C = CLi+ PhMe 2SiCHICH 3（HMPA/THF;产率，20%炔丙基硅烷）; H2/Pd-BaSO 4得到Z硅烷，95：5 Z：E。E硫化物：E-烯丙基氯+ PhSNa/EtOH，70%。Z-硫化物：（Z）-烯丙醇+Bu 3 P/PhSSPh/CH 3CN，20 ℃，86%（1：1 Z/E）。(6)类似物A值比较：Me 3Si，2.5 kcal/mol：Kitching，W.; Olszowy，HA; Drew，G. M. J. Org. Chem. 1982，47，5153。RS02，2.5 kcal/mol; RS，0.8 kcal/mol; Corey，E. J.道：Feiner，N. F. J.Org.Chem.1980，45，765和其中的参考文献。CH3S，1.0 kcal/mol：Eliel，E. L.的; Kandasamy，D.同上，1976，41，3899。
However, 1 should be destabilized in Z alkenes (R= alkyl) and higher selectivity for product I would be expected for the E isomers (R= H). This is contrary to Kishi’s findings. If—interactions are important, they can betested by com-paring the osmylation of substrates having bulky donor (X= PhMe2Si) vs. bulky acceptor (X= RS02) substituents. 5 Both the E and Z silanes should react via a geometry similar to 3 because the best-donor is also the largest substituent. 6 Appropriate type-I face selectivity is seen for the Z silane (Table I, entry 1) but the E silane reacts with selectivity for product II! 7 In the case of sulfones, geometry 2 should be best with donor CH3 “anti” and bulky acceptor (X= RS02) in the “outside” position. Appropriate selectivity for II is seen for E sulfones (entries 4 and 6), but again the Z isomers show type-I selectivity. It is hard to believe that highly congested 1 should be favored for Z sulfones regardless of electronic effects. Thus, one of the two olefin isomers (5) Preparation of E silane: PhSiMe2Li+(£> allylic chloride (THE), 51%, 9: 1 E/Z. Z silane: CH3C= CLi+ PhMe2SiCHICH3 (HMPA/THF; yield, 20% propargyl silane); H2/Pd-BaS04 gives Z silane, 95: 5 Z: E. E sulfide: E-allylic chloride+ PhSNa/EtOH, 70%. Z-sulfide:(Z)-allylic alcohol+ Bu3P/PhSSPh/CH3CN, 20 C, 86%(1: 1 Z/E).(6) Analogous A value comparisons: Me3Si, 2.5 kcal/mol: Kitching, W.; Olszowy, HA; Drew, G. M. J. Org. Chem. 1982, 47, 5153. RS02, 2.5 kcal/mol; RS, 0.8 kcal/mol; Corey, E. J.; Feiner, N. F. J. Org. Chem. 1980, 45, 765 and references therein. CH3S, 1.0 kcal/mol: Eliel, E. L.; Kandasamy, D. Ibid. 1976, 41, 3899.