Diisopropylamine steric hindrance

Camphorsulfonyl chlorides 45 readily form amides by reaction with amines. On reduction of the carbonyl group, alcohols, e.g., 46 and 47, are obtained which are extremely useful auxiliaries for many purposes. Thus, esters are formed with carboxylic acids which may then undergo enolate reactions (SectionsD.1.1.1.3.2., D.l.5.2.1., D.3. and D.7.1.) or act as dienophiles and dipolar-ophiles (Sections D.l.6.1.1.1.2.2.1. and D.l.6.1.2.1.). Enol ethers of these auxiliaries give [2 + 2] cycloadditions with dichloroketene (Section D.l.6.1.3.), while carbamate derivatives have been used in acyliminium reactions (Section D.l.4.5.). Generally, steric hindrance in the sulfonamide group improves the stereoselectivity of the reactions and, therefore, the amides with diisopropylamine and dicyclohexylamine are used as auxiliaries both enantiomers of the dicyclohexyl derivative are commercially available. 

By comparison, the acid-base reaction of 30 and 2 path b ) proceeds smoothly to give enolate anion 27 (the conjugate base) and diisopropylamine (the conjugate acid). There is little steric hindrance to the approach of the proton on the a-carbon, and 30 is a strong base. In other words, the acid-base reaction of 30 and 2 proceeds readily to form the enolate anion, but acyl addition to form 31 is so slow that virtually no 31 is formed. Since lithium diisopropylamide is a good base hut a poor nucleophile, it is termed a non-nucleophilic ha.se. Non-nucleophilic amide bases such as 30 are used when the acid is very weak, as with simple ketones and aldehydes, and acyl addition is a competitive reaction to deprotonation. When the pKj, of the aldehyde or ketone falls below 10, weaker bases can be used, but those reactions will be introduced when it is appropriate. 

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