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Nicolaou classics in total synthesis 1996 3 free

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Unformatted text preview:   Radical ­radical couplings –  Hydrogen ­atom transfers •  Actual reacFon pathway taken by a transient free radical intermediate is determined by a subtle balance of reacFon rates. Nicolaou, Classics in Total Synthesis, 1996 3 Free Radical Reactions Intramolecular radical addi*on Intermolecular radical addi*on R –  Could have rate problems •  Prefer intramolecular –  AcFvaFon entropies less negaFve than intermolecular –  Especially good for •  Construc*ng highly hindered C ­C bonds •  Construc*on of quarternary stereogenic centers Nicolaou, Classics in Total Synthesis, 1996 4 Free Radical Reactions •  OH and CN funcFonal groups do not need to be protected –  Rate of carbon radicals reacFng with carbonyl groups very slow due to the C ­O π bond strength •  C ­O bond and C ­N bond very resistant to homolyFc cleavage •  β ­posiFon trialkylaFon groups , halogens, thiols, sulfoxides readily eliminated –  In contrast to polar processes •  Carbanions do not tolerate oxygenated funcFonal groups at the β ­posiFon •  High levels of...
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