3, 5-dialkoxy

Acidic conditions are more favorable than thermal ring-closure for the formation of 5-substituted isomers. The isomeric ratio of 5- and 7-substi-tuted quinolines is less sensitive to conditions of ring closure in the case of A/r-(3-alkoxy- or 3,4-dialkoxy- or 3,4-alkylenedioxophenyl)aminomethy-lenemalonates (see Table V and following discussion). 

In the intense search for inhibitors of gastric acid secretion a new class of potent histamine H2-receptor antagonist was discovered. These 1,2,5-thiadiazole-l-oxides (27) were prepared by nucleophilic addition of primary amines to 3,4-dialkoxy-l,2,5-thiadiazole 1-oxide (25). Sequential addition of two different amines to positions C(3) and C(4), respectively, could be achieved via the 3-alkoxy-4-amino adduct (26) (Scheme 5) <82JMC207,82JMC210>. 

Mit wiiBrigem Ammoniak erha.lt man aus 3,4-Dialkoxy-furazan-2-oxiden das 3,4-Bis-[amino-carbonyl -furazan-2-oxidi0S A1° (mit gasformigem Ammoniak bzw. Piperidin in Diethylether tritt Ringumwandlung ein409). 

Dimethoxyfuran is readily available from the enolic dimethyl 3,4-dihydroxyfuran-2,5-dicarboxylate. This intermediate, like a phenol, can be readily O-methylated or O-benzy-lated. Hydrolysis and decarboxylation then furnishes the 3,4-dialkoxy compounds (78HCA430). The dimethoxy compound readily enters into Diels-Alder reactions, the Man-nich reaction, and may be lithiated. On mild acid hydrolysis it supplies, in poor yield, 4-methoxyfuran-3(2/f)-one and not tetrahydrofuran-3,4-dione, which is not produced by attempted hydrogenolysis of 3,4-dibenzyloxyfuran either. The dione, however, is known, and surprisingly exists in the diketo form (60JA3219). 

Yoshizawa et al. synthesized new types of taper shaped molecules by attaching two or three rod-like aromatic cores to the end of the alkyl chains of 3,4-dialkoxy benzoates and 3,4,5-trialkoxy benzoates, respectively, and having a perfluorinated chain at the apex examples of such molecules are shown in Fig. 69. 

Shulgin, A.T. Psychotomimetic amphetamines Methoxy 3,4-Dialkoxy-amphetamines. Experientia, 20 366-369, 1964. 

Deltic esters, i.e. 2,3-di-rerr-butoxycycloprop-2-enone (6a) and 2,3-diisopropoxy cycloprop-2-enone (6b) were also prepared by photodecarbonylation of the corresponding 3,4-dialkoxy-cyclobut-3-ene-l, 2-diones in 10-13% yield. The 2-alkoxy-3-alkylcycloprop-2-enones 5 were... 

The two geminal methyl groups attached to C-2 in dihydropyranocoumarins allow stereochemical assignments. In the angular 3, 4 -diols (N3 4 -l and N3"4 -26) the difference of the 13C chemical shifts of these methyl groups is larger than 3 ppm in the cis- and smaller than 2 ppm in the nrnr-isomer. This seems to be a rule which holds also for 3, 4 -dialkoxy substituents (87). 

Shulgin, A.T. 19648. Psychotomimetic [jfe] amphetamines Methoxy-3, 4-dialkoxy-amphetamines Experientia 20 3 66-367. 

Dialkoxy-phenyl Indole Phospho diesterase inhibitors Biased et alP... 

Hegde PK, Adhikari AV, Manjunatha MG, Sandeep CSS, Philip R. Nonlinear optical studies on new conjugated poly2,2 -(3,4-dialkoxy-thiophene-2,5-diyl) bis[5-(2-thienyl)-1,3,4-ox-adiazolejs. J Appl Polym Sci 2010 222 2641-50. 

Cheng, H. and R.L. Elsenbaumer. 1995. New precursors and polymerization route for the preparation of high molecular mass poly(3,4-dialkoxy-2,5-thienylenevinylene)s Low band gap conductive polymers. / Chem Soc Chem Commun 1451. 

J. S. Lomas, A. Adenier, K. Gao, F. Maurel and J. Vaissermann, Hydrogen bonding and steric effects on rotamerization in 3,4-aUcylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyldi(tert-butyl)-methanols an NMR, IR and X-ray crystallographic study, /. Chem. Soc., Perkin Trans. 2 (2), 216-224 (2002). 

The Mannich reaction of 3,4-dialkoxy-thiophenes was investigated [153] several Mannich bases and bis-Mannich bases were obtained under standard conditions secondary amine and aqueous formaldehyde (37%) in glacial acetic acid (Scheme 98) [153]. 

Highly soluble conjugated polymers poly(2,6-(dithieno[3,2-Z> 2, 3 -J] thiophenyl)-alt-2,5-(3,4-dialkoxy)thiophenyl) (288a,b) were produced by Stille cross-coupling of 282 with 2,5-bis(trimethyltm)-3,4-dialkoxythiophenes (287a,b) in moderate yields (Scheme 72) [111]. 

An interesting example of the influence of the number and positions of substituents on the thermodynamic polymerizability was provided by studies of cationic polymerization of 3,4-dialkoxy-THF. When two substituents were in cis-position, polymers with DP up to 35 could be obtained while trans-monomer essentially did not polymerize. As shown in Scheme 34, if substituents in cyclic monomer are in ds-position, there is a considerable additional strain due to their steric repulsion this strain is partly released when a rigid cyclic monomer is converted to a polymer chain in which, due to free rotation around carbon-carbon and carbon-oxygen bonds, the strain can be minimized. In trans-monomers, steric repulsion is considerably lower thus the gain in enthalpy is less significant. 

Some of the most promising alternative candidates were oxygen substituted, for example, for the polymers from monoalkoxy- and 3,4-dialkoxy-substituted thiophenes (see Chapter 3). The oxygen-bearing substituent is able to stabilize free radical and positive charge carrying forms by further delocalization, as depicted in Figures 4.1 and 4.2. 

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