- Organosilicon compounds with functional groups proximate to silicon. XVII. Synthetic and mechanistic aspects of the lithiation of α,β-epoxyalkylsilanes and related α-heterosubstituted epoxides
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A series of α-heterosubstituted epoxides, , has been found to undergo lithiation in the temperature range of -75 to -115 deg C at the C-H bond of the epoxide.The substituent Z could be Me3Si, Ph3Si, n-Bu3Sn, Ph3Sn, PhSO2, (OEt)2PO and Ph; the groups R and R' were H, Ph and n-C6H13; and the lithiating reagents were n-butyllithium, t-butyllithium and lithium diisopropylamide in donor media of THF or TMEDA.The lithiation occurs with retention of configuration and the resulting lithio-epoxide is unstable above 0 deg C, decomposing in a carbenoid manner.The lithiation is facile except for compounds where Z and R (an alkyl or aryl) are cis-oriented; where Z = R3Sn, lithiation occurs by tin-lithium, rather than hydrogen-lithium, exchange.The lithio-epoxides thereby generated can be quenched with various reagents to yield epoxides where the epoxide H has been replaced by D, Me3Sn, R, RCO and COOH.The utility of this procedure in organic synthesis is emphasized.Finally, the possible explanations for the acidity of such α-heterosubstituted epoxides and for the relative stability of the derived lithio-epoxides are considered and assessed.
- Eisch, John J.,Galle, James E.
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- Reactions of (triphenylsilyl)ethylene oxide with Grignard reagents (and with MgBr2). A reinvestigation
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Reactions of (triphenylsilyl)ethylene oxide (1) with simple Grignard reagents such as EtMgBr and PhMgBr have been reported to yield crystalline hydroxysilanes assigned as the α-hydroxy silanes expected from β opening of the epoxide. Reinvestigation of these reactions showed that the hydroxysilanes were the β-hydroxy silanes 4 and 7 expected from a rearrangement-trapping sequence; a bromohydrin, assigned as the α-bromo-β-hydroxy silane 9 from α opening, and (triphenylsilyl)acetaldehyde (8) were also formed.
- Hudrlik, Paul F.,Ahmed, Mohamed E.,Roberts, Ralph R.,Hudrlik, Anne M.
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p. 4395 - 4399
(2007/10/03)
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