Tetronate synthesis

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... 

Scheme 7.43 Tetronate synthesis by domino addition/Wittig olefination.

This is an example of a tetronate synthesis from an a-hydroxy ester and ylide 11. Equipment... 

A more recent report discussed a microwave-assisted tetronate synthesis entailing domino addition/Wittig olefinations of polymer-bound a-hydroxy esters with the cumulated phosphorus ylide Ph3P=C=C=0 [59]. The desired immobilized a-hydroxy esters can be obtained by microwave-mediated ring opening of the corresponding glycidyl esters by OH-, NH-, or SH-terminal polystyrenes of the Merri-... 

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]. 

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... 

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). 

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).

Effenberger and coworkers have utilized the tolerance of methyl ketones by the recombinant enzyme to develop an alternative synthesis of tetronic acids and their amino derivatives, as shown in Figure 5.18. Treatment of O-acyl cyanohydrins with lithium disilazide resulted in base-induced ring closure to amino tetronic acid derivatives. Alternatively, the cyanohydrins could be converted to a-hydroxy esters prior to acylation, and the same base-induced cyclization then led to tetronic acid derivatives [89]. 

Duffield, J.J. and Regan, A.C. (1996) Asymmetric synthesis of tetronic acids by Blaise reaction of protected optically active cyanohydrins. Tetrahedron Asymmetry, 7, 663-666. 

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. 

An intramolecular photocyclization approach has been developed for the synthesis of strained tetrahydrofuran and tetrahydropyrrole derivatives from tetronates (Table 1) <2004EJO4582, 2005JOC9798>. The cycloaddition reaction is not sensitive toward the degree of substitution on either reactive center and produces a single diastereoisomer in all cases (Equation 42). 

Diels-Alder reactions.1 A key step in a synthesis of 4-demethoxydaunomy-cinone (5) involves a regioselective Diels-Alder reaction of anthracene-1,4,9,10-tetrone (2) with (1) to give the desired adduct (3) in 79% yield. A similar reaction with 2-acetoxy-1,3-butadiene affords only a 58% yield of the corresponding adduct. The product (rather unstable) is aromatized and hydrolyzed to give 4 in high yield. 

Pyrimido[5,4-d]pyrimidine-2,4,6,8-tetrones X-ray crystal structure, 3, 339 Pyrimido[4,5-d]pyrimidine-4-thiones P 3, 339 synthesis, 3, 349... 

Clemo, N. G. Pattenden, G. Vinylic carbanions in synthesis. Novel synthesis of iso-gregatin B, iso-aspertetronin A and related O-methyl tetronic acids. Tetrahedron Lett. 1982, 23, 585-588. 

So, if the ester is enolisable, use the Me3SiCl method. If it isn t enolisable you don t need to. The a-diketones 57 were needed for the synthesis of tetronic acids. Changing the oxidation level of one ketone reveals a symmetrical acyloin 58 derived from the esters 59. 

The Claisen ester enolate reaction has proved to be extremely useful in the synthesis of a large number of natural products.3 In addition, the rearrangement has been extended to allow the preparation of useful intermediates such as a-alkoxy esters,88 329 33 336 343 a-phenylthio esters,339344-345 a- and [3-amino acids,340 346-350 a-fluoro esters,351 cycloalkenes,352353 tetronic acids,354 and dihydro-pyrans.355-357... 

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