Aldol condensation Stobbe reaction

Stobbe reaction org chem A type of aldol condensation reaction represented by the reaction of benzophenone with dimethyl succinate and sodium methoxide to form monoesters of an a-alkylidene (or arylidene) succinic add. shtob-3 re.ak shan ) stoichiometry phys chem The numerical relationship of elements and compounds as reactants and products in chemical reactions., st6i ke am-3 tre )... 

Two consecutive aldol condensations between a 1,2-dicarbonyl compound and diethyl thiodiacetate give thiophenes. The immediate product is an ester-acid, produced " by a Stobbe-type mechanism, but the reactions are often worked up via hydrolysis to afford an isolated diacid. 

The entire manifold of aldol-type condensation reactions. The aldol condensation itself (Equation 9.45, el seq) and all of those in Table 9.5 (viz. the Claisen, Stobbe, Perkin, and Knovenagel condensation reactions and the Robinson annulation). 

The first step of the Stobbe condensation is the deprotonation of the succinate at the a-carbon to afford an ester enolate that in situ undergoes an aldol reaction with the carbonyl compound to form a 3-alkoxy ester intermediate. The following intramolecular acyl substitution gives rise to a y-lactone intermediate which undergoes ring-opening and concomittant double bond formation upon deprotonation by the alkoxide ion. Under certain conditions the lactone intermediate can be isolated. 

The venerable Hinsberg synthesis (e.g. Scheme 42) [71] involves two consecutive aldol cmidensations between a 1,2-dicarbonyl compound and diethyl 2,2 -thiobisacetate and produces thiophenes carrying ester and carboxylic acid groups at the 2- and 5-positi(Mis, respectively, via a Stobbe-type mechanism [72]. Reactions are often worked up via hydrolysis to afford a diacid as the isolated product. Scheme 43 indicates a reasonable sequence for the condensation and explains the formation of an acid-ester product. 

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