Abstract:We have developed a practical crossed Claisen condensation between ketene silyl acetals and methyl esters using catalytic NaOH to obtain alpha-monoalkylated beta-keto esters and inaccessible alpha,alpha-dialkylated beta-keto esters.
“…This reaction is categorized into two types: (i) traditional base-mediated condensations using MOR (M = Na, K), LDA, MHMDS (M = Li, Na, K), and MH (M = Na, K) 2 and (ii) the Ti-Claisen condensation ). ,, 1 Traditional Claisen Condensation Using α-Mono- and α,α-Disubstituted Esters…”
[Structure: see text] A powerful Ti-crossed Claisen condensation between ketene silyl acetals (KSAs) and acid chlorides was successfully performed to give alpha-monoalkylated esters and thermodynamically unfavorable (less accessible) alpha,alpha-dialkylated beta-keto esters in good yield (46 examples; 41-98% yield). A closely related reaction between ketene silyl thioacetals (KSTAs) and acid chlorides also proceeded smoothly to give alpha-monoalkylated and alpha,alpha-dialkylated beta-keto thioesters (21 examples; 61-97% yield). The present protocol was extended to the direct condensation of KSAs with carboxylic acids (14 examples; 71-97% yield).
“…This reaction is categorized into two types: (i) traditional base-mediated condensations using MOR (M = Na, K), LDA, MHMDS (M = Li, Na, K), and MH (M = Na, K) 2 and (ii) the Ti-Claisen condensation ). ,, 1 Traditional Claisen Condensation Using α-Mono- and α,α-Disubstituted Esters…”
[Structure: see text] A powerful Ti-crossed Claisen condensation between ketene silyl acetals (KSAs) and acid chlorides was successfully performed to give alpha-monoalkylated esters and thermodynamically unfavorable (less accessible) alpha,alpha-dialkylated beta-keto esters in good yield (46 examples; 41-98% yield). A closely related reaction between ketene silyl thioacetals (KSTAs) and acid chlorides also proceeded smoothly to give alpha-monoalkylated and alpha,alpha-dialkylated beta-keto thioesters (21 examples; 61-97% yield). The present protocol was extended to the direct condensation of KSAs with carboxylic acids (14 examples; 71-97% yield).
“…3 As a synthetic application of these silyl enolates, methyl and tert-butyl ester-derived KSAs were utilized for the first base-catalyzed crossed-Claisen condensation with simple methyl esters (Scheme 3). 4 In connection with these topics, we present herein three subjects: (i) a new practical preparation of relevant (Z)-ketene silyl thioacetals (KSTAs), (ii) that of alkyl (1Z)-or (1Z,3E)-1,3-bis(TMS)-dienol ethers, (iii) full details of NaOH-catalyzed crossed-Claisen condensation, 4 and (iv) titanium-mediated Claisen-aldol tandem reactions of the obtained b-ketoester analogues. KSTAs 1 are relevant isosteres of KSAs.…”
“…In this chemistry, it is also known that silicon enolates, such as ketene silyl acetals (KSAs), are applicable to obtain the desired 1,3-dicarbonyl products (Scheme 1, formation of I). [1] In similar reactions, silyl acetals, which are simple adducts of the silicon enolates of the starting esters, are often isolated (Scheme 1, formation of II).…”
By choosing the organic acid catalysts, the reaction of lactones with ketene silyl acetals results in selective formation of simple Mukaiyama aldol adducts or olefination products, which are formed by the subsequent elimination of a silanol from the adducts. That is, in the presence of acidic zwitterions, the reaction of lactones with ketene silyl acetals gives simple Mukaiyama aldol adducts in excellent yields. In contrast, the same reaction in the presence of a carbon acid catalyst brings about the formation of olefination products in a Z‐selective manner.
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