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190 Organic Chemistry Solutions Manual Suggested solution The product was used at the US The very strong base BuLi will first remove the OH proton and then the alkyne proton. The alk Department of Agriculture to make anion is more reactive (last formed, first to react) and is alkylated. Hydrogenation goes for the pheromone of the Douglas Fir tussock moth (G. D. Daves and alkyne first and adds a molecule of hydrogen to the same side of the triple bond to give a cis alke: group, J. Org. Chem., 1978, 43, 2361). OH BuLi OLi BuLi OLI Li Problem 8 These two Wittig reactions (Chapter 14) give very different results. The first gives a single alkene in high yield (which?). The second gives a mixture from which one alkene can be separated with difficulty and in low yield. Why are they so different? D 0 + Ph₃P CHO Ph₃P + 0 part of mixture o Purpose of the problem A demonstration of good and bad selectivity for you to unravel. The question of alkene geometry Suggested solution from the Wittig reaction is discussed Both Wittig reagents have carbanions that are further stabilized by carbonyl groups and should in Chapter 31. E-alkenes selectively. The first example reacts with the aldehyde rather than with the ester to give This product was used to make a trans enal in good yield. human leukotriene at Smith, Kline, and French in Philadelphia (J. G. Gleason et al., Tetrahedron MeO₂C CHO Lett., 1980, 21, 1129). + Ph₃P CHO MeO₂C CHO The problem was solved by a 3 group in Adelaide who made the natural product freelingyne in this In the second example, the electrophile is an anhydride with two reactive carbonyl groups that way (C. F. Ingham et al., Aust. J. nearly but not quite the same. This is a recipe for bad selectivity - reaction will occur at Chem., 1974, 27, 1477). carbonyls. In addition, stereoselectivity will not be so good as the alkenes are trisubstituted there is not as much difference in stability between cis and trans as there was in the enal. Problem 9 Why is this particular amine formed by reductive amination? OMe OMe Na(CN)BH₃ MeO N H pH 5.5 CHO OMe Purpose of the problem Extending the concept of reductive amination by combining it with deprotection and