Lithium cyclohexyl isopropyl amid

Substituted sulfinyl esters (6) have also been prepared by this reaction using the same base or lithium cyclohexyl-(isopropyl)amide, which gives higher yields. 

This contrasts to thiomethylation of methyl 9-oxodecanoate with MeSSMe and lithium cyclohexyl(isopropyl)amide, as reported by Trost. In spite of various reaction conditions employed, Trost s procedure gives less than 30% yield of 2-methylthio-9-oxodecanoate, accompanied by bissulfenylation when the 9-oxo group is not protected. Moreover, toxic HMPA is required to obtain 86% of the sulfenylated ester even when the 9-oxo group is protected. The transformation described in eqs 1 and 2 works with PhSS02Ph as well. 

In 1989 Oppolzer reported that the enolates of A-acyl sultams derived from camphor afford highly diastereoselective alkylation products with a variety of electrophiles including those which are not allylically activated [88]. The sultam is deprotonated using either butyllithium with a catalytic amount of cyclohexyl isopropyl amine, or butyllithium alone, or sodium hexamethyldisilyl amide.As illustrated in Scheme 3.18, alkylation occurs selectively from the Re face of the Z(( )-enolate to give monoalkylated sultams which can be cleaved by LAH reduction or lithium hydroperoxide catalyzed hydrolysis. Representative examples are listed in Table 3.7. 

Lithium-diisopropylamid (LDA) in THF/Hexan ist das Reagenz der Wahl zur Erzeugung der Carbonsaure-enolate. In vielen Fallen wird HMPTA als Cosolvens zugesetzt515,516. Eine Kombination von Natriumhydrid und LDA ist ebenfalls wirksam516. Weiterhin wur-den andere Lithium-amide fur diesen Zweck eingesetzt, so z. B. Lithium-dimethyl-, -diethyl- und -dicyclohexyl-517, -bis-[trimethylsilyl]-5lS, -cyclohexyl-isopropyl-519 oder -di-tert.-butyl-amid520. 

Figure 3.3. LDA = lithium diisopropyl amide, LICA = lithium isopropyl cyclohexyl amide, LTMP = lithium tetramethylpiperidide, LHDS = lithium hexamethyldisilyl amide.

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