3.6- dimethyl-4-hydroxy-2-pyrone

A product of tbe tropolone-producing mold PenidUium stipitatum was identified as 3,6-dimethyl-4-hydroxy-2-pyrone by its conversion to 3,6-dimethyl-4-hydioxy-2-pyridone (W-257) with ammonia in a sealed tube at 120 and to tbeiV-methyl-2-pyridone with aqueous methylamine. ... 

Dimethyl-4-hydroxy-2-pyri-done, from 3,6-dimethyl-4-hydroxy-2-pyrone, 659... 

Carboxy-, 5-dimethyl nitrobenzene, AP11 Carboxyferrocene, ATl6 2-Carboxy-3-hydroxy- -pyrone,... 

Fig. 9. Normalized solubilities of l,2-dimethyl-3-hydroxy-4-pyridinone, dmppH, of its aluminum(III) and iron(III) complexes AKdmppla and Fe(dmpp)s, and of the 3-hydroxy-4-pyronate complexes Ga(malt)3 and In(etmalt)3 in methanol-water mixtures at 298.2 K (data from Refs. (114) and (234)).

Pyrone, 3-hydroxy-2-methyl Sd (roasted) Pyrrole, 1-5-dimethyl Sd (roasted) Pyrrole, 1-ethyl Sd (roasted) ... 

As shown in Scheme 15, 4-substituted 4-hydroxy-2,6-dimethyl-4//-pyrans 324 and 325 were obtained by reaction of 4-pyrone 322 with BuLi320 or substituted furyllithium reagents,321 respectively. 4,4-Disubstituted 2,6-dimethyl-4//-pyrans 326 were prepared by the reaction of a threefold excess of the corresponding Grignard reagents RMgX with 4-pyrone 322.3 1,316... 

Industrially, a selectivity to DAA of between 90—95% can be achieved (64). The principal by-products are mesityl oxide and acetone trimers. j W-Triacetone dialcohol [3682-91-5] can form by condensation of acetone with diacetone alcohol (116). Dehydration of ry/ -triacetone dialcohol can yield semiphorone [5857-71-6] (6-hydroxy-2,6-dimethyl-2-hepten-4-one), which may in turn ring close to form 2,2,6,6-tetramethyl-y-pyrone [1197-66-6/, or ultimately dehydrate to phorone [504-20-1] (2,6-dimethyl-2,5-heptadien-4-one) (146). Similarly, an unsymmetrical acetone trimer can also be formed which dehydrates to 2,4-dimethyl-2,4-heptadiene-6-one. These impurities complicate the high purity recovery of DAA, and are thought to be responsible for a yellow discoloration of DAA. The addition of dibasic acid (147) or nitrogen containing carboxylic or phosphonic acids (148) has been patented as refined product stabilizing agents. 

Dimethyl-4-hydroxy-tetrahydro-IV/lc, 351 (4H-Pyron-Hydrier ) VI/4, 41, 65 (Hydrier.)... 

In another approach, the a-pyrone ring was made by Michael addition of dimethyl malonate to 3j -hydroxy-21-oxo-20-methylenepregn-5-ene (506),... 

The allylalkohol 6 turns out to be the obvious precursor of the protected diol 5, and 6 reasonably arises from a Shapiro coupling of cyclohexadienyllithium 7 with the cyclohexene-4-aldehyde 8 which is the product of oxidation and subsequent diol protection of the bicyclic hydroxylactone 9 the latter emerges from rearrangement of the Diels-Alder cycloadduct 13 of 3-hydroxy-2-pyrone 14 as the diene and 4-hydroxy-2-methyl-2-butenoate 15 as the electron-deficient dienophile. The cyclohexadienyllithium 7 originates from the sulfonylhydrazone of the ketone 10 which is, once again, a Diels-Alder cycloadduct of the protected 3-hydroxymethyl-2,4-dimethyl-l,3-pentadiene 12 and ketene 11 as the dienophile. 

In order to prepare the cyclohexenaldehyde 8, 3-hydroxy-2-pyrone 14 and ethyl 4-hydroxy-2-methyl-2-butenoate 15 are subjected to a Diels-Alder reaction in the presence of phenylboronic acid which arranges both reactants to the mixed boro-nate ester 19 as a template to enable a more efficient intramolecular Diels-Alder reaction with optimal control of the regiochemical course of the reaction. Refluxing in benzene affords the tricyclic boronate 20 as primary product. This liberates the intermediate cycloadduct 21 upon transesterification with 2,2-dimethylpropane-l,3-diol which, on its part, relaxes to the lactone 22. Excessive i-butyldimethyl-silyltriflate (TBSTf) in dichloromethane with 2,6-lutidine and 4-7V,A-dimethyl-aminopyridine (DMAP) as acylation catalysts protects both OH goups so that the primary alcohol 23 is obtained by subsequent reduction with lithiumaluminum-hydride in ether. 

Amidines from amide acetals. N-Dimethyl-acetamide diethyl acetal added to a stirred suspension of 2-amino-6-carbethoxy-3-hy-droxy-4-pyrone in abs. acetone, and the product isolated after 3-4 hrs. N-(6-carbethoxy -3- hydroxy -4- pyron-2- yl)-N, N -dimethylacetamidine. 

Dehydroacetic acid oxime rearrangesinpolyphosphoricacidto 3-acetamid04 hydroxy-6-methyl-(2ff)-2-pyrone and 2,6-dimethyl-(4 0 Pyrano[3,4-d] oxazol-4-one (W-242). Treatment of W-242 with ammonia gives 2,6-dimethyl-(5//)-oxazolo[4,5-c]-4-pyridone, which, in turn, gives 3-acetamido4-hydroxy-6-methyl-2-pyridone with hydrochloric acid at room temperature and 3-amino-4-hydroxy-6-methyl-2-pyridone on heating. ... 

Acetylacetone and malonyl chloride give 5-acetyl-4-hydroxyd-methyl-2-pyrone (XII-253), a positional isomer of dehydroacetic acid, which reacts with aqueous ammonia or aqueous methylamine to form XII-254 (R = H, CHs), which can also be prepared from the enamine of acetylacetone and carbon suboxide (see Section I.3.E., p. 635). The //-methylpyridone XII-2S4 (R = CH3) is deacetylated to 4-hydroxy-l,6-dimethyl-2-pyridone with sulfuric acid however, W-254 (R = H) was not deacetylated under these conditions. Acetylacetone and carbon suboxide give 8-acetyl-4-hydroxy-7-methylpyrano-[4,3-6] pyiane-2,5-dione (XI-255) with catalytic amounts of sulfuric acid. This is also formed from acetylacetone and malonyl chloride or from carbon suboxide and the intermediate 5-acetyl-4-hydroxy-6-methyl-2-pyrone (XU-253). 3,5-Diacetyl-4-hydroxy-6-methyl-2-pyrone (XI-256) can be formed by acetylation of XII-253 with acetic acid and phosphorus oxychloride or by degradation of XII-255. 3,5-Diacetyl-4-hydroxy-6-methyl-2-pyridone can... 

C14H14O3, DL-4-Methoxy-6-styryl-5,6-dihydro-a-pyrone, 38B, 335 Cl4H14O3, 1,2,3,4,4a,5,8,8a-Octahydro-1,4,5,8-exo,exo-dimethanonaph-thalene-4a,8a-dicarboxylic anhydride, 46B, 320 C1ftH1flOa, cis-2-Hydroxy-2,4-dimethyl-3,4-dihydro-2H,5H-pyrano[3.2-c][1]benzopyran-5-one, 45B, 332... 

Hydroxy-5-oximino-7-methyl-5i/-pyrano[2,3-6]pyridine 8-oxide, formed by the action of dimethylformamide dimethyl acetal on 3-acetyl-4-hydroxy-6-methyl-a-pyrone, has been shown by C n.m.r. to exist as structure (153), one of... 

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