Acetoacetic 2,2-dimethyl-, decarboxylation

To complete the section on the synthesis of 4,4 -bipyridines, we summarize the methods reported for the preparation of some substituted 4,4 -bi-pyridines and 4,4 -bipyridinones. These methods are closely analogous to syntheses already discussed for some of the isomeric bipyridines. Thus the Hantzsch reaction using pyridine-4-aldehyde, ethyl acetoacetate, and ammonia gives 3,5-di(ethoxycarbonyl)-1,4-dihydro-2,6-dimethyl-4,4 -bipyridine, which after oxidation, followed by hydrolysis and decarboxylation, afforded 2,6-dimethyl-4,4 -bipyridine. Several related condensations have been reported. Similarly, pyridine-4-aldehyde and excess acetophenone gave l,5-diphenyl-3-(4-pyridyl)pentane-l,5-dione, which with ammonium acetate afforded 2,6-diphenyl-4,4 -bipyridine. Alternatively, 1-phenyl-3-(4-pyridyl)prop-2-enone, A-phenacylpyridinium bromide, and ammonium acetate gave the same diphenyl-4,4 -bipyridine, and extensions of this synthesis have been discribed. Condensation of pyridine-4-aldehyde with malononitrile in the presence of an alcohol and alkaline catalyst produced compounds such as whereas condensations of... 

The self-condensation of /3-keto esters and related compounds occurs under the influence of either acidic or basic catalysts and constitutes one of the earliest syntheses of pyran-2-ones (l883LA(222)l). It exemplifies a synthesis of type (ii) (Scheme 85). Ethyl acetoacetate, for instance, gives a mixture of 4,6-dimethyl-2-oxopyran-5-carboxylic acid and its ethyl ester other esters behave similarly (59RTC364). Decarboxylation of the pyrancarboxylic acid occurs at 160 °C in sulfuric acid. The formation of the pyranone proceeds through a 5-keto ester which is considered to result from attack of the enolic form of the ester on protonated ethyl acetoacetate (51JA3531). A detailed synthesis of the pyran-5-carboxylic acid is available <630SC(4)549). 

Dimethyl-4-carbethoxy-2-cyclohexen-l-one and 3,5-di-methyl-2-cyclohexen-l-one have always been prepared from acetaldehyde and acetoacetic ester through the Knoevenagel condensation.2 The keto ester has previously been obtained by selective saponification and decarboxylation methods which have involved heating the crude condensation product with water at 140° 2 3 or with sodium ethoxide in alcohol.3 The ketone has been obtained from the same condensation product by prolonged refluxing in 20% sulfuric acid.2-4 6... 

Two new alkaloids have been isolated from Burley tobacco Nicotiana tabacum L.) condensate, and their structures elucidated mainly on mass and n.m.r. spectral evidence. Structure (38) has been assigned to one and confirmed by two syntheses, one of which involves the exhaustive aeetylation of isophorone (39) with aeetie anhydride-perchlorie acid to the pyrylium salt (40). Ammonolysis of the salt yielded the alkaloid (38). The second alkaloid, formulated as (41), was synthesized from 5,5-dimethyl-2-cyclopenten-l-one (42) via Michael addition of ethyl acetoacetate to give, after hydrolysis and decarboxylation, (43). Regioselective acetalization then... 

Reaction of [2- " C]acetone with vinylmagnesium bromide (Figure 6.75, Procedure A) provided 2-methyl-3-[2- " C]buten-2-ol (257), which upon treatment with PBra rearranged to give 3,3-dimethyl[3- " C]allyl bromide (258). The latter was used for the alkylation of ethyl acetoacetate, thereby extending the carbon skeleton of the /3-keto ester by a labeled five-carbon (isoprenyl) unit. The initially formed alkylated intermediate 259 was not isolated but immediately saponified and decarboxylated to give ketone 260. Subsequent Homer-Wadsworth-Emmons olefination and reduction of the separated trans-ester 261 converted 260 into [T- Clgeraniol 12621. 

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