Tetronic acid, reaction with

Few reports concern complexes of the hydrazones of furantriones. Thus, reaction of 3-phenylhydrazones-5-methyltetronic acid 54 and 3,4-bis(phenylhydrazones)-5-methyl tetronic acid 65b with rrflns-[Pd(NH3)2] gave complexes whose analytical results were consistent with the formulae [Pd(54)2] and [Pd(65b)2(N 113)2], respectively (83MI6). 

To a solution of alkyl aryllacetate (1 2.0 mmol) and alkyl hydroxyacetate (2 2.2 mmol) in DMF (10 mL) was added a 1 M solution of KOt-Bu in THF (4.4 mL, 4.4 mmol). The mixture was then stirred under argon at room temperature for 2-16 h. On completion of the reaction, the reaction mixture was poured into cooled 1 N HCl (15 mL). The aqueous phase was extracted with ethyl acetate (3 x 10 mL), and the combined organic layers was washed with brine, dried over Na2S04. After filtration and concentration in vacuo, the residue was purified by column chromatography to furnish tetronic acid 3 with 39-96% yield. All the products were characterized from spectral analyses. 

The Reforrnatsku reaction of a-halogenated carboxylic esters with silylated cyanohydrins combined with an intramolecular acylation reaction gives fluorinated derivatives of tetronic acid [28] (equation 17) It is noteworthy to mention that this particular reaction sequence only proceeds with ultrasonic irradiation A very... 

The allylation reaction of the optically active tetronic acid derivatives 146 was shown to give a variety of isomers depending on the reaction conditions (temperature and reaction time) (Scheme 44 and Table I) (99H1321). The reaction is carried out by treating 146 with allyl bromide in DMF and in the presence of K2CO3. 

The reaction of a nitrile with a Reformatsky reagent is known as the Blaise reaction and when applied to (9-trimethylsilyl cyanohydrins leads to the formation of tetronic acids with high ee [79]. By working-up the Blaise reaction with ammonium chloride it is possible to isolate... 

This review of furan chemistry is meant to continue the earlier survey by Bosshard and Eugster1 and concentrates upon the period 1968 to the end of 1979. Like the earlier review, this one is limited to the chemistry of the monocyclic furan nucleus and does not deal, except incidentally, with fused rings such as benzofuran or its quinones. Nor does it deal in detail with dihydro- or tetrahydrofurans, nor with compounds like furylpyridine that contain some other heterocyclic nucleus as well. Some butenolides and tetronic acids are admitted to consideration since they are the carbonyl equivalents of hydroxyfurans regarded as enols, but side-chain reactions are wholly excluded unless the furan nucleus clearly affects them in some important way. 

Me2S04 or Et,S04 (17.3 mmol) is added with vigorous stirring to the TBA-tetronate (16.5 mmol) prepared by the addition of aqueous TBA-OH (0.5 M, 3.5 ml) to the appropriate tetronic acid (16.5 mmol) and evaporation to dryness under reduced pressure, in CH2C12 (70 ml). The mixture is stirred until the reaction is complete and the solvent is then evaporated. H,0 (50 ml) is added to the residue and the aqueous solution is continuously extracted with Et20 for ca. 3 h. The ethereal extract is washed with aqueous NaHCO, dried (MgS04), and evaporated to give the 4-alkoxy-5H-furan-2-one (R = H,... 

Partially hydrogenated quinoline cores are also present in some important bioactive compounds. For example, the 4-aza-analogs of Podophyllotoxin, a plant lignan that inhibits microtubule assembly, revealed to be more potent and less toxic anticancer agents. In 2006, Ji s group reported a green multicomponent approach to a new series of these derivatives, consisting of the reaction of either tetronic acid or 1,3-indanedione with various aldehydes and substituted anilines in water under microwave irradiation conditions (Scheme 26) [107]. For this efficient and eco-friendly transformation, the authors proposed a mechanism quite similar to the one that was postulated for the synthesis of tetrahydroquinolines in the precedent section. 

As mentioned above, cyclic / -diketones such as cyclohexane-1,3-dione and other cyclic / -dicarbonyl compounds are known to function well in Biginelli condensations (see Figure 4.3). However, for tetronic acid the reaction takes an entirely different course, following a pseudo-four-component pathway to furnish spiro het-erobicydic products in good yields (Scheme 4.11) [158], The reaction proceeds by a regiospecific condensation of two molecules of aldehyde with the other reagents... 

The synthesis of medicinally relevant 4-substituted 2(5//)-furanones has been achieved by a coupling reaction of the triflate derived from p-tetronic acid with alkyl-and cyclopropylboronic acids (Scheme 10.8).22 This reaction was mediated by bis(acetonitrile)dichloropalladium and silver oxide. Interestingly, optically active cyclopropyl boronic acids were not racemized during this coupling reaction. 

Acid derivatives including esters, amides, halides and nitriles are readily accessible. Dicyanofuroxan (72) shows in its reactions some similarities to phthalonitrile (75LA1029) it also provides a source of fused pyridazino- and oxazino-furoxans (73) and (74) via addition with hydrazine and hydroxylamine, respectively (82H(19)1063). The tetronic acid compound (75) yields a hydroxyamide (76) on aminolysis (79S977). 

The lithium enolates from tetronic acid-derived vinylogous urethanes have been generated and their reactivity investigated with a variety of electrophiles (eq 5). The reactions proceed with excellent regio- and diastereoselectivity and a variety of alkylating agents can be utilized. 

Tetronic acids and P-keto-y-butyrolactones are easily prepared by reaction of an 0-trimethylsilylated cyanohydrin with a-bromo esters in the presence of a Zn- u couple in a Reformatsky-type reaction (Scheme 12). ... 

Keto-y-butyrolactones teironic acids Zinc, activated with Cu(OAc)2, promotes a Reformatsky-type reaction of a-bromo esters with O-silylated cyanohydrins to provide p-keto-y-butyrolactones or tetronic acids. 

O-Alkyltetronic acids.- Preparation of these compounds from the parent tetronic acids under mild conditions relies on the exchange reaction with isoureas derived from DCC. 

The lithium enolate derived from angelica lactone (LDA, THF, - 78 °C) reacts as a Michael acceptor exclusively at the y-position thus the butenolide (65) is obtained from ethyl acrylate. Surprisingly, in view of this finding, reaction with methyl iodide results in mixtures of the a-methyl and aa-dimethyl derivatives. Similar results have been obtained with the enolates of 2- and 3-methylbut-2-enolides which undergo prenylation by dimethylallyl bromide at both the a- and y-positions. By contrast the tetronic acid derivative 3-methoxy-2-methylbut-2-enolide is alkylated only at the y-position to give (66) in high yields. 

Tetronic acid has been prepared in three steps from enamines derived from 4-chIoroacetoacetate, and 2,4-dialkyltetronic acids are produced in good yield by ozonolysis of 2,6-dialkyl-3,5-dihydroxy-l,4-benzoquinones. ° The vinyl-lithium (72) can be obtained from the parent enamine by reaction with Bu Li. ° Subsequent condensation with alkaryl ketones and cyclization leads to the tetronic acid derivatives (73) in 20—50% yield. 

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