lecture 16.3

lecture 16.3 - 16-16-1Organic Organic...

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Unformatted text preview: 16-16-1Organic Organic ChemistryChemistryWilliam H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson16-16-2Aldehydes Aldehydes & & KetonesKetonesChapter 16Chapter 1616-16-3Acetals as Protecting GrpsAcetals as Protecting GrpsSuppose you wish to bring about a Grignard reaction between these compounds5-Hydroxy-5-phenylpentanal(racemic)4-BromobutanalBenzaldehyde??+HOHOHOHOBr16-16-4Acetals as Protecting GroupsAcetals as Protecting Groupsa Grignard reagent prepared from 4-bromobutanal will self-destruct!first protect the -CHO group as an acetalthen do the Grignard reactionhydrolysis (not shown) gives the target moleculeHOBrA cyclic acetal+H+H2OHOOH+BrOOBrOO1. Mg, ether2. C6H5CHOOOO-MgBr+A chiral magnesium alkoxide(produced as a racemic mixture)16-16-5Acetals as Protecting GroupsAcetals as Protecting GroupsTetrahydropyranyl (THP) protecting groupthe THP group is an acetal and, therefore, stable to neutral and basic solutions, and to most oxidizing and reducting agentsit is removed by acid-catalyzed hydrolysisRCH2OH+OORCH2ODihydropyranA tetrahydropyranyletherH+THP group16-16-6Addition of Nitrogen NucleophilesAddition of Nitrogen NucleophilesAmmonia, 1 aliphatic amines, and 1 aromatic amines react with the C=O group of aldehydes and ketones to give imines (Schiff bases)...
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This note was uploaded on 03/30/2008 for the course CHEM 262 taught by Professor Forbes during the Spring '08 term at UNC.

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lecture 16.3 - 16-16-1Organic Organic...

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