Tetronics

Chemoselective C-alkylation of the highly acidic and enolic triacetic acid lactone 104 (pAl, = 4.94) and tetronic acid (pA, = 3.76) is possible by use of DBU[68]. No 0-alkylation takes place. The same compound 105 is obtained by the regioslective allylation of copper-protected methyl 3,5-dioxohexano-ate[69]. It is known that base-catalyzed alkylation of nitro compounds affords 0-alkylation products, and the smooth Pd-catalyzed C-allylation of nitroalkanes[38.39], nitroacetate[70], and phenylstilfonylnitromethane[71] is possible. Chemoselective C-allylation of nitroethane (106) or the nitroacetate 107 has been applied to the synthesis of the skeleton of the ergoline alkaloid 108[70]. 

A number of these stmctures are offered commercially by BASE Corporation under the trade name Tetronic polyols. The products are similar to oxygen block polymers. Although not strongly surface active per se, they are useful as detergents, emulsifiers, demulsifiers, defoamers, corrosion inhibitors, and lime-soap dispersants. They are reported to confer antistatic properties to textiles and synthetic fibers. 

Table 1 Hsts the polyether antibiotics arranged by the number of carbons in the skeleton. Many of these compounds were isolated independendy in separate laboratories and thus have more than one designation. The groups are subdivided depending on the number of spiroketals. Two classes fall outside this scheme the pyrrole ether type containing a heterocycHc ring, and the acyltetronic acid type, that has an acyHdene tetronic acid instead of a carboxyHc acid. These compounds are ionophores and because of their common features are included as polyethers.

The purely chemical analogy involving nucleophilic attack and subsequent oxidation can be achieved by hydrogen peroxide, which converts pteridin-6-one into pteridine-6,7-dione (52JCS1620), and xanthopterin (4) into leucopterin (6) (39LA(539)179). Isoxanthopterin (5) reacts with nitrous acid to give pteridine-2,4,6,7-tetrone (44LA(555)146). 

Pyrimido[5,4-d]pyrimidine-2,4,6,8-tetrone X-ray, 3, 339 (66JCS(A)639> Pyrimido[4,5-d]pyrimidine-4-thione pK 3, 339 (58JOC1451) Pyrimido[4,5-d]pyrimidine-2,4,7-triamine,... 

Butenolide, 2-hydroxy — see Isotetronic acids Butenolide, 3-hydroxy — see Tetronic acids But-2-enolide, 4-alkylidene-synthesis, 4, 697 Butenolides H NMR, 4, 578 mass spectrometry, 4, 585 structure, 4, 551 synthesis, 1, 416 trimethylsilylation... 

Pteridine-2-sulfonic acid, 4-oxo-3,4-dihydro-synthesis, 3, 300 Pteridine-2,4,6,7-tetrone formation, 3, 308 reactions, 3, 296 synthesis, 3, 291... 

Pyrimido[ 1,2-a]pyrimidine-1,4,6,9-tetrones rearrangement, 3, 341 Pyrimido[4,5-d]pyrimidine-2,4,5,7-tetrones synthesis, 3, 364... 

Alloxan [2,4,5,6(l//,3//]pyrimidine, tetrone] [50-71-5] M 142.0, m 170 (dec), pK 6.64. Crystn from water gives the tetrahydrate. Anhydrous crystals are obtained by crystn from acetone, glacial acetic acid or by sublimation in vacuo. 

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing... 

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... 

Methoxyethoxymethyl, 365 Enamino Derivatives, 365 4-Methyl-1,3-dioxolanyl Enol Acetate, 365 Pyrrolidinyl Enamine, 365 Benzyl Enol Ether, 366 Butylthio Enol Ether, 366 Protection of Tetronic Acids, 366 Trimethylsilyl Enol Ether, 367... 

Calculated Energies for o-Tetronic Aqd (B3LYP/Basis)" (99UP1)... 

The synthesis of a selenonium ylide with a tetronic acid anion moiety was reported (83TL75 84CPB2666). 3-Enamino-tetronie aeids have also been investigated (82SC431). 

For 3-acetylthiotetronic acid the same type of tautomerization process (90 91, 92 93 as a result of prototropy between internal tautomers 90, 91 92, 93, rotation of the side-chain group, between external tautomers) was observed as for the corresponding 3-acetyl-tetronic acids ( H NMR, NMR) [76JHC533 78BCJ651 79JCS (P2)1605],... 

As has already been pointed out for 3-acyl-tetronic and -thiotetronic acids, the corresponding 3-acyl-tetramic acid can exist as internal tautomers (136 137,138 139) as a result of prototropy between the two oxygen atoms and as external tautomers (136,137 138,139) as a result of rotation of the side-chain acyl group. 

Tetronic acids exist predominantly in the dioxo form (32) in solvents of low polarity, while the existence of the monoenol form (33) has been established in other solvents by infrared " and ultraviolet spectral comparisons- and from dipole moment data. " Haynes and Pliramer " have recently reviewed the structure of these compounds [see also reference 28(a)], and the tautomerism of vitamin A (34), which has a related structure, has also been surveyed.- Analogous compounds carrying an amino group in the 3-position are also know n. ... 

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. 

Recently, the Michael addition of the optically active Q ,y-disubstituted tetronic acids 146c,e with a variety of Q ,/3-unsaturated aldehydes, ketones, esters, and nitriles was studied (Scheme 53) (99H1321). 

Dehydrobromination of 12 to -tetronic acid (13) in high yield could be achieved only under narrowly circumscribed conditions 62). The molar ratio of barium hydroxide to 12 needed to solubilize 12 and to neutralize the liberated hydrobromicacid must be at least two to one. Deionized water was the preferred solvent because of ease of workup. The yields were found to be concentration dependent. Concentrations of 12 in water of about 16% gave good yields of 13, whereas at 33% concentration the yield was much lower. One gram of 10% Pd-on-C per 33 g of 12 was required less catalyst gave incomplete reductions. 

Pluronic and Tetronic Surfactants, BASF Technical Literature (1989). 

Schemes 16-19 present the details of the enantioselective synthesis of key intermediate 9. The retrosynthetic analysis outlined in Scheme 5 identified aldoxime 32 as a potential synthetic intermediate the construction of this compound would mark the achievement of the first synthetic objective, for it would permit an evaluation of the crucial 1,3-dipolar cycloaddition reaction. As it turns out, an enantioselective synthesis of aldoxime 32 can be achieved in a straightforward manner by a route employing commercially available tetronic acid (36) and the MEM ether of allyl alcohol (74) as starting materials (see Scheme 16).

Ketal 73 can be formed in a yield of about 60 % by refluxing a solution of tetronic acid (36), ethylene glycol, and a catalytic amount of para-toluenesulfonic acid in benzene for approximately 12 hours. With only one electrophilic site, 73 reacts smoothly with Dibal-H to give lactol 35 in 84% yield. Compound 35, a participant in a ring-chain tautomeric equilibrium process,18 should be regarded as a latent aldehyde. This substance can, in fact, serve as... 

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