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454 Organic Chemistry Solutions Manual Suggested solution Following the usual mechanism (pp. 1330-4), the palladium complexes to the face of the alkene opposite the bridge and the ester group leaves to give an allyl cation complex. This is attacked by the malonate anion from the opposite face to the palladium. So the overall result is retention, the starting material giving the cis product. 0 0 CO₂Me CO₂Me CO₂Me LnPd CO₂Me CO₂Me CO₂Me This investigation helped to The racemization comes from the structure of the allyl cation complex. It is, in fact, symmetric establish the mechanism of these reactions: B. M. Trost and with a plane of symmetry and attack occurs equally at the two ends of the allyl system giving the two N. R. Schmuff, Tetrahedron Lett., enantiomers of the product. 1981, 22, 2999. CO2H attack from left attack from right MeO₂C MeO₂C CO₂Me CO₂Me CO₂Me CO₂Me PdLₙ CO₂Me CO₂Me Problem 6 Revision of Chapter 47. The synthesis of a bridged tricyclic amine shown below starts with an enantiomerically pure allyl silane. Give mechanisms for the reactions, explaining how the stereochemistry is controlled in each step. N Br SiMe₂Ph Br H RHN Znl₂ CHO + NR Ph₃P N N RN Purpose of the problem Revision of allyl silane chemistry (pp. 1296-300) and the stereochemistry and mechanism of an intramolecular Heck reaction. Suggested solution The first reaction is a Lewis-acid-catalysed reaction between the amine and the aldehyde and addition of the allyl silane to the resulting iminium salt. Addition occurs at the other end of the allylic system and on the opposite face to the silicon. The most obvious way to put the reagents together looks excellent until we realize, from the Newman projection, that the two Hs in the product would then be anti whereas they are actually syn. Br Br Br H H PhMe₂Si PhMe₂Si H N H N R N NR R N N