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Kinetics regioselective directed lithiation

Directed lithiations of a,3- and -y.b-unsaturated amides " have been extensively studied. Illustrative examples are shown in Scheme 44. Prior complexation of the alkyllithium base with the amide carbonyl oxygen directs the base to the thermodynamically less acidic -position in a,3-unsaturated amide (31), which adds to benzophenone and subsequently lactonizes. Analysis of the NMR spectrum reveals that the organolithium added the benzophenone in the equatorial position. A Afferent kinetic deprotonation is seen in y,8-unsaturated amide (32), where -lithiation to form an allylic anion predominates over a-lithiadon to form an enolate. > Addition of the lithium anion to acetone affords poor regioselectivity, but transmetalation to magnesium before carbonyl addition yields a species which adds exclusively at the 8-position. ... [Pg.480]

See other pages where Kinetics regioselective directed lithiation is mentioned: [Pg.252]    [Pg.350]    [Pg.350]    [Pg.164]    [Pg.497]    [Pg.502]    [Pg.177]    [Pg.123]    [Pg.28]    [Pg.32]    [Pg.461]    [Pg.461]    [Pg.38]    [Pg.27]    [Pg.7]    [Pg.461]    [Pg.480]   
See also in sourсe #XX -- [ Pg.629 , Pg.630 , Pg.631 ]



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