Decarboxylation Stobbe product

The. synthesis starts with the Stobbe condensation of diethylsuccinate and 3,4-dichloroben-zophenone (13). The product (14) is hydrolyzed and decarboxylated to a cis-trans mixture of olefins (15). This last is reduced using a Pd/C catalyst and then undergoes unidirectional Friedel-Crafts intramolecular acylation into the more reactive ring to produce substituted tetralone 16. 

The dicarboxyic acid 66 (alkylidenesuccinic acid), obtained by hydrolysis and decarboxylation of the triester 65, resembles the product (half-ester) 73 of the Stobbe condensation (Scheme 11-21) [21]. In order to prepare the half-ester, carbonylation in benzyl alcohol to prepare the monomethyl ester and dibenzyl ester 75, followed by hydrogenolysis of the dibenzyl ester, was attempted, expecting the formation of the halfester. However, /S-keto ester 76 was obtained, an entirely different product (Scheme 11-22) [22]. The mechanism of this unexpected reaction is unknown. 

The formation of a side chain at C14 of the ketone (53) has the object of synthesizing the acid (67), which has been obtained by several methods (Scheme 7). In the first of these, a three-carbon side chain is introduced in two stages, the Reformatskii reaction and Arndt—Eistert lengthening of the chain, via the intermediate (66) [143, 195]. The Reformatskii reaction of ketone (53) with p -bromopr op ionic ester enables the acid (67) to be obtained in one stage [195-198]. Finally, the third method of synthesizing (67) comprises the Stobbe reaction and decarboxylation of the reaction product (70) accompanied by a shift of the double bond into the A -position [199]. 

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