2.4- Dihydroxy-2, 5-dimethyl-3

Figure 9 presents routes leading to major products in the cysteine/glucose experiments at pH values of 5 - 7. Thiofuraneol and 2,4-dihydroxy-2,5-dimethyl-3(2H)-thio-phenone were formed as major components at a ratio of 10 1. All other thiophenes were minor constituents. 

Recently, 2,4-dihydroxy-2,5-dimethyl-3(2ff)-thiophenone (DHDMT) was identified in soy sauce as a low-molecular-weight pigment formed by the MaiUard reaction (11BBB1240). Murata et al. (13FF1076) discovered that DHDMT contributed color, aroma, and functional properties to food, and was formed more from cystine than cysteine. It was detected in various brown foods (roasted brown rice) and beverages (beer, but not coffee).The authors su ested that the various kinds of reductants formed during the MaiUand reaction (98FSTIT258) reduced cysteine to cystine, which subsequently leads to DHDMT formation. 

R)-Pantothenic acid (1) contains two subunits, (R)-pantoic acid and P-alanine. The chemical abstract name is A/-(2,4-dihydroxy-3,3-dimethyl-l-oxobutyl)-P-alanine (11). Only (R)-pantothenic acid is biologically active. Pantothenic acid is unstable under alkaline or acidic conditions, but is stable under neutral conditions. Pantothenic acid is extremely hygroscopic, and there are stabiUty problems associated with the sodium salt of pantothenic acid. The major commercial source of this vitamin is thus the stable calcium salt (3) (calcium pantothenate). 

Benzo[b]furan, 2,3-dihydro-2-phenyl-synthesis, 4, 697 Benzo[b]furan, 2,3-dihydroxy-tautomerism, 4, 37 Benzo[6]furan, 4,6-dimethoxy-acylation, 4, 606 Benzo[6]furan, 2,3-dimethyl-acetylation, 4, 606 bromination, 4, 605 photooxygenation, 4, 642 Benzo[b]furan, 5,6-dimethyl-2,3-diphenyl-applications, 4, 709 Benzo[b]furan, 1,3-diphenyl-vertical ionization potential, 4, 587 Benzo[b]furan, 2-ethoxy-5-hydroxy-synthesis, 4, 127... 

Pyrazine, 2,5-dichloro-3,6-difluoro-synthesis, 3, 190-191 Pyrazine, dihydro-, 3, 177 Pyrazine, 1,2-dihydro-oxidation, 3, 178 reduction, 3, 177 Pyrazine, 1,4-dihydro-antiaromaticity, 3, 177-178 synthesis, 3, 177 Pyrazine, 2,3-dihydro-oxidation, 3, 178 Pyrazine, 2,5-dihydro-synthesis, 3, 178 Pyrazine, 3,6-dihydro-synthesis, 3, 184 Pyrazine, 2,5-dihydroxy-oxidation, 3, 175 Pyrazine, 2,3-dimethyl-1,4-dioxide... 

Dichloroquinazolines have been prepared from the corresponding 2,4-dihydroxy compounds by heating for a few hours with phosphorus oxychloride in the presence of dimethyl aniline or phosphorus penta-chloride. These are more stable than the monochloro compounds and can be distilled in vacuum without appreciable decomposition. 

Demethylation of trequinsin (3) with a 65 35 mixture of AcOH and 48% HBr at 115 °C for 3 h gave mainly 10-hydroxyl derivatives 148 (R = r = H), which was accompanied by traces of its 9-hydroxyl and 9,10-dihydroxy derivatives. In boiling 48% HBr for 2 h its 9,10-dihydroxy derivative formed in 63% yield (98IJC(B)1). 9-Methoxy group of 3 and that of its 2-[(2,6-dimethyl-4-carboxyphenyl)imino] derivative 178 (R = COOH) was selectively demethylated by the treatment with 60% NaOH and EtSH in HMPA. Treatment of 3 with pyridine HCl in boiling pyridine for 20 min afforded its 9,10-dihydroxy-3-desmethyl derivative in 65% yield. 4 -Hydroxymethyl... 

Chamical Nama 7-(2,3-Dihydroxypropyl)-3,7-dihydro-1,3-dimethyl-l H-purine-2,6-dione Common Nama (1,2-Dihydroxy-3-propyl)theophylline diprophylline... 

Dimethyl l, 5-dimethoxy-3-methyl-3//-3-bcnzazepinc-2,4-dicarboxylate (mp 108-110 C) can be obtained in 31 % yield by the methylation of dimethyl l,5-dihydroxy-3-methyl-3A/-3-ben-zazepine-2,4-dicarboxylate (see Section 3.2.1.1.1.) with diazomethane.14... 

Cyclocondensation of 3,4-dihydroxy-2,5-furandicarboxylate dimethyl ester 205 with acetohydrazidehydrazone hydrochloride 206 gave 207 (89LA105) (Scheme 44). 

Figure 1 shows the structure of pantothenic acid ((R)-(+)-N-(2,4-dihydroxy-3,3 -dimethyl-1 -oxobuty 1-13-alanine). Only D(+)-pantothenic acid occurs naturally and is biologically active. The alcohol (R)-pantothenol (= (D)-panthenol) shows biological activity as well. 

The rigid and soft blocks used in polyesteredier diermoplastic elastomers (polyesteretlier TPEs) are typically PBT and poly(oxyteti amethylene) (PTMO), respectively, witii block number-average molar mass varying between 1000 and 3000. They are obtained by the melt reaction between dimethyl terephthalate, butanediol, and dihydroxy-terminated PTMO in the conditions typical of a PBT syndiesis. 

Polyester-Polyether Thermoplastic Elastomers Dimethyl Terephthalate/l,4-Butanediol/Dihydroxy-Poly(oxytetramethylene)... 

Alkin-ole werden ebenfalls selektiv zu Alken-olen reduziert (s. a. Bd. V/lc, S. 467). So erhalt man z. B. aus 5-Hydroxy-5-methyl-hexin-(l)-en-(3) an einer Kupfer/Silber-Ka-thode in Athanol/Natriumcarbonat 80-90% d.Th. 5-Hydroxy-5-methyl-hexadien-(l,3)2. Dagegen tritt beim 2,7-Dihydroxy-2,7-dimethyl-octadiin-(3,5) an einer Kupfer-Kathode in Athanol/Natronlauge gleichzeitig Wasser-Abspaltung und Isomerisierung ein und man gewinnt 7-Hydroxy-2,7-dimethyl-octadien-(2,4) (39% d.Th. Kp2 70-720)3 ... 

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