Keto esters condensation with

P-Keto esters condense with pyridines in the presence of FeCL. 

Keto esters condense with conjugated oximes at 150°-160° to afford substituted pyridines in the presence of FeCIa- ... 

Kirsch has reported the conversion of propargyl vinyl ethers to form pyrroles via a multi-step transformation involving the silver-catalyzed propargyl Claisen rearrangement to form the a-allenyl P-keto ester, condensation with a primary aryl amine. 

A piridazine ring forms the nucleus for a rather unusual nontricyclic antidepre.ssant. Condensation of the keto ester 136 with hydrazine leads to the cyclic hydrazide 137. Oxidation, for example with bromine, gives the corresponding pyridazone 138. The oxygen is then replaced by chlorine by reaction with phosphorus oxychloride. Displacement of the halogen in 139 with N-ethylami-nomorpholine affords minaprine 140 [30]. 

In the course of a synthesis of ( )-nootkatone the keto-ester (148) with ethylidenetriphenylphosphorane gave the cyclohexanone (149), a Dieckmann condensation having occurred under the basic conditions. Among other natural products synthesized using Wittig reagents are... 

Three-cmbon ring expansionThe cyclic p-keto esters 1 with a 4-oxopentyl group at the a-position do not undergo the expected aldol condensation on treatment with KOC(CH3)3 in DMSO, but undergo ring expansion to medium-size ketones (2). The reaction may involve aldol and retro-aldol condensation. A similar... 

Treatment of the /3-keto ester 220 with sodium ethoxide at elevated temperature triggered off an epoxide ring opening by / -elimination that was followed by the desired Knoevenagel condensation to afford the tricyclic product 206 (Scheme 34). The enone moiety in the intermediate 221 did not show a propensity for deprotonation and, therefore, the ketone carbonyl function of the enone moiety was available for a Knoevenagel condensation. The reduction of the p-keto ester (206) to the corresponding diol was the next objective. Treatment of the TES-protected -keto ester (TES-206) with DIBAH afforded the diastereomeric diols 222 and 223 in a moderate diastereoselec-tivity in favour of the undesired diastereomer 222. The diastereomers were separated and the undesired diastereomer 222 was epimerized to 223 by a sequence that consists of Mitsunobu inversion and benzoate ester reduction [98, 99]. 

Condensation of 3-nosyloxy-2-keto esters 305 with methyl carbamate in refluxing toluene in the presence of p-toluenesulfonic acid provides 2(3/7)-oxazolone -carboxylates 306 in good yields (41-80%). Alternatively, condensation of 3-bromo-2-keto esters 307, derived from the bromination of a-keto esters with CuBr2, with methyl carbamate in the presence of AgOTf and p-toluenesulfonic acid under similar conditions provides the 2(3//)-oxazolone-4-carboxylates 306 in comparable yields (30-79%) (Fig. 5.78 Table 5.15, Fig. 5.79). ... 

The versatile Knorr pyrrole synthesis is an important route to pyrroles 169 it involves the condensation of a -keto ester 167 with an -amino ketone 168 (Scheme 95). The -keto ester can be replaced by a -diketone simple ketones give poor yields. The amino ketone is frequently prepared in situ by nitrosation and reduction (e.g., with Zn—AcOH) of a second molecule of the -keto ester. 

Acetoacetic ester condenses with aldehydes at S-IO in the presence of piperidine, piperidine acetate, or acetamide. Several olefinic -keto esters have been made in this way for example, ethyl butylideneaceto-acetate (81%). ... 

We wondered if this reaction might be exploited to construct the angularly condensed benzo[a]anthracenes. A problem was the aromatization of the initially formed hydroaromatic ring A under the relatively drastic basic reaction conditions. The starting material 12 was synthesized in a stepwise manner from l-hydroxy-5-methoxy-9,10-anthraquinone [23]. The crucial cyclization can mechanistically be regarded as an intramolecular nucleophilic displacement of the methoxy group to afford a keto ester 13 with about 55% yield (Scheme 5). Only a few nucleophilic additions to electron-deficient anthraquinones are known [20,24,25] and intramolecular reactions of this type are more facile [21, 26-30]. The subsequent ethoxydecarbonylation under acidic conditions to yield ketone 14 presented no problem. 

Derivatives of 8-phenyl-2,3-dihydroimidazo[l,2-a]pyridin-7-one (322) were prepared by the condensation of a series of /S-keto esters (320) with 2-benzylimidazoline (321) <78JHC1021). 

An interesting condensation has been reported in which a 2-pyridyl-l,3-butanedione (53a) reacts with /3-aminoacrylonitrile (54) to provide 3-cyano-4-(trifluoromethyl)tpy (55) in 30% yield (Scheme 10).57 The reaction has been used employing a wide variety of partners besides those involving 2-pyridyl. The Hantzsch approach has been used in the reaction of keto-ester (53b) with enone (56) to provide (57), where the 2-furfuryl group may be oxidized under mild conditions to provide the 3, 4 -tpy dicarboxylic acid.58... 

Stream of nitrogen. The initial product, the jS-keto sulfoxide II, undergoes intramolecular ester condensation with formation of the 1,3-indanedione system. Ill, which in the presence of hydrochloric acid undergoes Pummerer rearrangement to 2-chloro-2-methylmercapto-l,3-indanedione (IV). This crystalline product (m.p. 63°) is obtained in yield of 80% and is hydrolyzed in boiling water nearly quantitively to ninhydrin (V). 

With keto-ester condensations the procedure of first converting the ketone to be acylated to its sodio derivative and then adding the acylating ester, employed previously with sodium amide (1) has generally not been satisfactory with sodium hydride, as considerable self-condensation occurs. The general method adopted for mixed condensations by sodium hydride consists in slowly adding the com-... 

The Davidson oxazole synthesis describes the preparation of substituted oxazoles 2 from the condensation of / -keto-esters 1 with ammonia or ammonium acetate. A general reaction scheme is depicted below. 

In the late nineteenth century, Ludwig Claisen (Germany 1851-1930) treated an ester with a base the isolated product was a P-keto ester. This product results from the enolate anion of one molecule of the ester condensing with a second molecule via an acyl substitution reaction (Chapter 16, Section 16.8). In a typical experiment, ethyl 2-methyl propionate (60) is treated with a specialized base (sodium triphenylmethide, 19) in diethyl ether and stirred at room temperature for 60 hours. This reaction mixture is then acidified with glacial acetic acid (i.e., 100% acetic acid) the final isolated product is ethyl 2,2,4-tri-methyl-3-oxopentanone (61) in 74% yield. It is clear that when an ester enolate reacts with another ester, the product is a -keto ester and the reaction is now called the Claisen condensation. 

Keto-ester 61 results from self-condensation of the ester 60, but the reaction of two different esters under these conditions gives a different result. Condensation between two different esters is called a mixed Claisen condensation and it occurs when the enolate anion of one ester condenses with the second ester. Under thermodynamic conditions, however, the ester is always present along with the ester enolate because it is an equilibrium process. At equilibrium, there are two esters in the medium as well as two different ester enolates, and each enolate anion wiU react with both esters to give a different product. 

Condensations of keto-esters (177) with o-phenylene-bis-methylamine afford the pyrido- and pyrrolo-benzodiazepines (178a) and (178b), although entry into... 

D-Glucose condenses with ethyl acetoacetate and other /8-keto esters and with jS-diketones, in the presence of anhydrous zinc chloride, to give derivatives of furan 184), The constitution of some of the compounds has been verified by oxidation with lead tetraacetate 18S) and with periodate ion 186). The aldose would appear to react in the form of its 1,2-enediol. 

Ethyl benzoylacetate allowed to react with NaH in tetrahydrofuran, the resulting soln. added to a soln. of 2 equivalents dilithiobenzoylacetone prepared from benzoylacetone and 2 moles Li-diisopropylamide in tetrahydrofuran, and stirred 2 days at room temp. tetraketone. Y 51%. - The enolate salt of the y -keto ester condenses as electrophylic anion with strong nucleophiles such as the dianion of benzoylacetone. F. e. s. T. P. Murray and T. M. Harris, Am. Soc. 94, 8253 (1972) 95, 6865 (1973). 

A new synthesis of aldehydes with 2-methyl-2-thiazoline has the advantage of releasing the aldehydes from the thiazolidine intermediate under neutral conditions . Acetylene derivatives can be obtained from aldehydes via dibromomethylene compounds Novel reactions of alkynes with cationoid electrophiles have been published. -Diketones and 2-ketoalkoximes can be obtained by this reaction from acid chlorides and aliphatic nitro compounds respectively Addition of aldehydes to activated carbon-carbon double bonds occurs smoothly in the presence of cyanide ions as catalysts . Poly- -carbonyl compounds have been prepared by condensation of two anions, whereby the enolate salt of a y8-keto ester condenses as an electrophilic anion with strong nucleophiles such as the dianion of benzoylacetone. ... 

Mojtahedi and coworkers [76] performed a mild condensation of hydrazine derivatives with various p-keto esters under solvent-free conditions using ultrasound irradiation to S5mthesize pyrazolone derivatives within short reaction times and good yields. Pyrazolones are conventionally S5mthesized by the treatment of p-keto esters (76) with hydrazine substrates (77) under acidic conditions at elevated temperature [77,78] however, these authors reported a novel and environmentally safe procedure for rapid preparation of various pyrazolone derivatives (78) using ultrasound irradiation (Scheme 19). 

This reaction consists of the condensation of two molecular equivalents of a 1,3 diketone (or a J3-keto-ester) with one equivalent of an aldehyde and one of ammonia. Thus the interaction of ethyl acetoacetate and acetaldehyde and ammonia affords the 1,4-dihy dro-pyridine derivative (1), which when boiled with dilute nitric acid readily undergoes dehydrogenation and aromatisation" to gb e the diethyl ester of collidine (or 2,4,6-trimethyl-pyridine-3,5 dicarboxylic acid (II)). For the initial condensation the solid aldehyde-ammonia can conveniently be used in place of the separate reagents. 

The formation of ethyl acetoacetate is an example of a general reaction knowu as the acetoacetlc ester condensation in which an ester having hydrogen on the a-carbon atom condenses with a second molecule of the same ester or with another ester (which may or may not have hydrogen on the a-carbon atom) in the presence of a basic catalyst (sodium, sodium ethoxide, sodamide, sodium triphenylmethide) to form a p-keto-ester. The mechanism of the reaction may be illustrated by the condensation of ethyl acetate with another molecule of ethyl acetate by means of sodium ethoxide. ... 

The decarboxylation of allyl /3-keto carboxylates generates 7r-allylpalladium enolates. Aldol condensation and Michael addition are typical reactions for metal enolates. Actually Pd enolates undergo intramolecular aldol condensation and Michael addition. When an aldehyde group is present in the allyl fi-keto ester 738, intramolecular aldol condensation takes place yielding the cyclic aldol 739 as a main product[463]. At the same time, the diketone 740 is formed as a minor product by /3-eIimination. This is Pd-catalyzed aldol condensation under neutral conditions. The reaction proceeds even in the presence of water, showing that the Pd enolate is not decomposed with water. The spiro-aldol 742 is obtained from 741. Allyl acetates with other EWGs such as allyl malonate, cyanoacetate 743, and sulfonylacetate undergo similar aldol-type cycliza-tions[464]. 

Condensation of 2-hydrazinoseIenazoles with /3-keto esters (R,-CO-CHn-COOR) yields l- selenazol-2-yl)-3-alkylpyrazol-5-ones (Scheme 20) (34). 

The most widely used method for the preparation of carboxylic acids is ester hydrolysis. The esters are generally prepared by heterocyclization (cf. Chapter II), the most useful and versatile of which is the Hantzsch s synthesis, that is the condensation of an halogenated a- or /3 keto ester with a thioamide (1-20). For example ethyl 4-thiazole carboxylate (3) was prepared by Jones et al. from ethyl a-bromoacetoacetate (1) and thioformamide (2) (1). Hydrolysis of the ester with potassium hydroxide gave the corresponding acid (4) after acidification (Scheme 1). 

In a reaction related to the mixed Claisen condensation nonenolizable esters are used as acylatmg agents for ketone enolates Ketones (via their enolates) are converted to p keto esters by reaction with diethyl carbonate... 

The sequence begins with a Claisen condensation of ethyl pentanoate to give a p keto ester The ester is hydrolyzed and the resulting p keto acid decarboxylates to yield the desired ketone... 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

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