Methyl 2//-pyran-5-carboxylate

The C-mcthylation of methyl pyran-2-one-5-carboxylate (96) to methyl 6-methylpyran-2-one-5-carboxylate (97) can be in-... 

Elenolide. 4-(l-Formyt-l-propenyl)-3,4-dihydro-2-oxo-2H-pyran- -carboxylic acid methyl ester. 

Thieno[3,4-d]oxazole-3a(4H)-carboxylic acid, dihydro-2-methyl-synthesis, 6, 1020 Thieno[2,3-d Joxazoles synthesis, 6, 990 Thieno[3,2-g]pteridine structure, 3, 284 lH-Thieno[3,4-c]pyran-2-ones synthesis, 4, 1032 Thienopyrazines synthesis, 4, 1022-1024 Thieno[2,3-6]pyrazines, 4, 1023 electrophilic substitution, 4, 1024 Thieno[3,4-6]pyrazines, 4, 1024 Thieno[3,4-c]pyrazole, 4,6-dihydro-3-hydroxy-carbamates... 

Attempts to effect cycloaddition of 1/7-azepines with 2//-pyran-2-one have failed however, the more electron-deficient inethyl 2-oxo-2/7-pyran-5-carboxylate undergoes slow addition with ethyl 1//-azepine-1-carboxylate to give a mixture of the [2 + 4] 32 and [6 + 4] 33 7t-cycload-ducts.260 In contrast, prolonged reaction of methyl 1 //-azepine-1 -carboxylate with the isomeric... 

C24H25NO3S) see Saquinavir 2,2, 2",2 "-[(l,2,3,4-tetrabydro-8-piperidinopyrimido [5,4-(7]pyrimidine-2,6-diyl)dinitrilo]tetraetbanol (C19H35N7O4 13665-89-9) see Mopidamol tetrahydropyran-4-carbonyl chloride (CfjH9C102 40191-32-0) see Risperidone tetrahydropyran-4-carboxylic acid (C(jHio03 5337-03-1) see Risperidone [2-[(tetrahydro-2H-pyran-2-yl)oxy]ethyl]carbamodithioic acid methyl ester... 

Elaboration of triol 88b to bryostatin 7 requires chemoselective hydrolysis of the Cl methyl ester in the presence of the C7 and C20 acetates, macrolide formation, installation of the C13 and C21 methyl enoates, and, finally, global deprotection. The sequencing of these transformations is critical, as attempts to introduce the C21 methyl enoate to form the fully functionalized C-ring pyran in advance of macrolide formation resulted in lactonization onto the C23 hydroxyl. In the event, trimethyltin hydroxide promoted hydrolysis [73] of the Cl carboxylate of triol 88b, and subsequent trie thy lsilylation of the C3 and C26 hydroxyls each occurs in a selective fashion, thus providing the seco-acid 89. Yamaguchi macrolacto-nization [39] proceeds uneventfully to provide the macrolide 67 in 66 % yield (Scheme 5.14). 

Ring transformation involving the intramolecular reaction of a hydrazone or in situ formed hydrazone also appeared. The transformation of 6-methyl-2//-pyran-2,3,4-trione 3-arylhydrazones 332 into l-aryl-6-methyl-4-oxo-l,4-dihydropyridazine-3-carboxylic acids 333 is an example of the former (Scheme 82). Compound 332 are formed via reaction of 4-hydroxy-6-methyl-27/-pyran-2-one 331 with substituted benzenediazonium chlorides. These are normally not isolated and immediately used further <2005EJM1325>. An example where a hydrazone is formed in situ is the reaction of 2-amino-5-aryldiazenyl-4-oxo-6-phenyl-4//-pyran-3-carbonitriles 334 with H2SO4 in glacial acetic acid, yielding 2-aryl-6-benzoyl-3-hydroxy-5-oxo-2,5-dihydropyridazine -carbonitriles 335 (Scheme 83) <2001T6787>. 

Methyl-(lS,5S,7S,8R,9R)-l-(P-D-glucopyranosyloxy)-l, 5,6,7,8,9-hexahydro-7-hydroxy-8-methylcylopenta(c)pyran-4-carboxylate... 

Relatively stable 2,2,4,6-tetramethyl-2//-pyran (176) exhibited a high regiospecificity toward methyl propargylate to afford [47t + 27t] adduct 561, which spontaneously decomposed to methyl 2,4-dimethylbenzoate (562) in 73% yield.405 Similarly, labile 3-acetyl-2,6-dimethyl-2//-pyran (564) gave with acetylenic methyl carboxylates benzenoid derivatives 565. On the other... 

Methyl 2-methoxy-5,6-dihydro-2H-pyran-6-carboxylate (2 R = Me) can be obtained in optically active form by condensation of diene 1 with methyl glyoxylate in the presence of dichlorotitanium (R)-binaphthol catalyst (3) [45]. 

The nucleophilic carbon of diazomethane attacks the ring of pyran-2-ones, especially when electron-withdrawing substituents are present for example, methyl 2-oxo-pyran-5-carboxylate (methyl coumalate, 269) is methylated successively at C-6 and C-4... 

The second variant is the reaction of a pyran-2-one (methyl coumalate, 313) as dienophile with a cyclopentadiene (314). The balance between the dienic and dienophilic capabilities of pyran-2-one is tipped in favour of the latter by the electron-withdrawing properties of the carboxylic ester group and this fine balance enhances the potential of these compounds as synthons (72CC388). 

The pyran-4-one ring (whether annulated to benzene or not) exerts an effect on some attached groups, for example, on the ease with which protons are detached from methyl groups and on the pKa of some carboxylic acids. Annulation of a benzene ring to the pyran-4-one increases the latter s stability to electrophiles and the effect is even more marked when two benzene rings are fused to the pyran, as in xanthone. 

In a detailed study of the reaction of methylene ketones with carboxylic acids in the presence of polyphosphoric acid, pyran-4-ones were obtained from l,3-diphenylpropan-2-one, phenylpropan-2-one and pentan-3-one (61JA193). In the first case, formation of 2,6-dimethylpyran-4-one ( 14 R = H) rather than the 2-benzyl-6-methyl-3-phenyI isomer... 

H-Pyran-3-carboxylic acid, 2-oxo-, methyl ester 13C NMR, 3, 588 <800MR(13)244) 2H-Pyran-6-carboxylic acid, 2-oxo-, methyl ester 13C NMR, 3, 588 <800MR(13)244)... 

A mixture of potassium fluoride (33.83 g, 0.582 mol), 2,4 -dibromoacetophenone (80.93 g, 0.291 mol), and DMF (350 ml) was stirred at room temperature for 5 min. A solution of 4 1 mixture of (cis trans) acids (45.0 g, 0.265 mol) in DMF (50 ml) was then added to the reaction mixture and the whole stirred at room temperature for 3 h, then at 100°C for 30 min. The reaction mixture was cooled to room temperature and diluted with H20 (200 ml). The aqueous solution was extracted with Et20 (4x400 ml). The combined ethereal extracts were washed with H20 (3x400 ml) and dried over sodium sulfate. After the solvent was partially removed in vacuo, a precipitate was formed. The slurry was the filtered to give 51.0 g (53%) of p-bromophenacyl ester of 6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acids as a white solid material, melting point 137°-138°C. 

To a solution of the p-bromophenacyl ester of 6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acids (46.0 g, 0.125 mol) in glacial AcOH (650 ml) was slowly added zinc (dust, 49.31 g, 0.754 mol) in a 60 min-period at room temperature. The reaction mixture was stirred at room temperature for 8 h, then filtered on Celite, and the zinc residue washed with AcOH (200 ml), then THF (200 ml). Most of the solvent was evaporated and the crude reaction mixture diluted with Et20 and washed with H20 (2x150 ml). The organic layer was treated with a diluted NaOH solution to pH 10. The aqueous phase was washed with Et20 several times, then acidified with a 1.0 N HCI solution to pH 4, and extracted with Et20. The combined organic extracts were... 

To a stirred solution of the (+)-6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acid (3.0 g, 17.65 mmol) in CH2CI2 (60 ml), and DMF (0.12 ml) at 0°C was added oxalyl chloride (1.82 ml, 21.18 mmol) over a 30 min-period. The reaction mixture was stirred at 0°C for 1 h, then at room temperature for 2 h. The solvent was evaporated in vacuum, and the residue was used directly in the next reaction without further purification. In a 50 ml, two-necked, round-bottomed flask equipped with a Teflon-covered magnetic stirring bar, a drierite filled trap, and a thermometer was placed the crude acid chloride in HMPA (16 ml). Freshly prepared trans-propenyltrimethyltin (4.34 g, 21.18 mmol) was then added followed by the addition of... 

Pravastatin was isolated as products of enzymatic hydroxylation by some kinds of microorganisms of [lS-[l-a(R ),7p,8P(2S, 4S )8a 3]]-2-methylbutanoic acid l,2,3,7,8,8a-hexahydro-7-methyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2))-pyran-2-yl)ethyl]-l-naphthalenic lactone (campactin) or their carboxylic acid or their salts (products of animal metabolism of microorganisms from the genera Nocardia, Streptomyces et cetera). 

Methyl 6-oxo-5-phenyl-6/M,3,4-oxadiazine-2-carboxylate 657 reacts with alkenes to yield 2//-pyran-2-ones. The reaction proceeds via cycloaddition of 657 to the alkene to form the y-oxoketene intermediate 658 addition of bromine and bis-elimination of HBr then affords 2//-pyran-2-ones (Scheme 154 and 155) <1998J(P1)2031>. 

Carbomethoxypivaloylketene 733 can undergo a hetero-Diels-Alder reaction with ethoxyalkyne to yield methyl 2-fer/-butyl-6-ethoxyM-oxoM//-pyran-3-carboxylate (Equation 292). Likewise, carbomethoxypivaloylketene 733 undergoes a hetero-Diels-Alder reaction with ethoxyethene to afford the intermediate dihydropyran-4-one, which upon elimination of ethanol affords methyl 2- v/-butylM-oxo-4//-pyran-3-carboxylate (Scheme 185) <2001T6757>. 

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