Tetrahydrofurans 2.5- dimethoxy

In MeOH, l,4-dimethoxy-2-cyclohexene (379) is obtainejl from 1,3-cydo-hexadiene[315]. Acetoxylation and the intramolecular alkoxylation took place in the synthesis of the naturally occurring tetrahydrofuran derivative 380 and is another example of the selective introduction of different nucleo-philes[316]. In intramolecular 1,4-oxyacetoxylation to form the fused tetrahy-drofurans and tetrahydropyrans 381, cis addition takes place in the presence of a catalytic amount of LiCI, whereas the trans product is obtained in its absence[317]. The stereocontrolled oxaspirocyclization proceeds to afford the Irons product 382 in the presence of Li2C03 and the cis product in the presence of LiCl[ 318,319]. 

Alky]-5-imino-3-methy -A2-l,2,4-thiadiazoIines react exotherm ally at 0°C with dibenzoy] or dimethoxy carbonylacetylenes in tetrahydrofuran to give the 2-alkylaminothiazoles in high yields (1564). The cycio addition reaction of 2-pyridyl isothiocyanates with 1-azirines results in the formation of 2-pyridylaminothiazoles (1565). 

The conversion of furans by oxidative acetylation or methoxylation to 2,5-diacetoxy- or 2,5-dimethoxy-2,5-dihydrofurans respectively, and their subsequent hydrogenation to the corresponding tetrahydrofurans, provides a useful source of protected 1,4-dicarbonyl compounds capable of conversion inter alia into the other five-membered heterocycles [Pg.142]

Let us discuss now the conditions required for the electron transfer process. This reaction requires, of course, a suitable electron donor (a species characterized by a low ionization potential) and a proper electron acceptor, e.g., a monomer characterized by a high electron affinity. Furthermore, the nature of the solvent is often critical for such a reaction. The solvation energy of ions contributes substantially to the heat of reaction, hence the reaction might occur in a strong solvating solvent, but its course may be reversed in a poorly solvating medium. A good example of this behavior is provided by the reaction Na -f- naphthalene -> Na+ + naphthalene". This reaction proceeds rapidly in tetrahydrofuran or in dimethoxy... 

Als stark nucleophile Reagentien werden sie in Tetrahydrofuran Oder 1,2-Dimethoxy-athan als Losungsmittel zu folgenden Reduktionen eingesetzt ... 

The wide latitude of structural variation consistent with bioactivity in this series is illustrated by the observation that antiinflammatory activity is maintained even when the second aromatic group is attached directly to the pyrrole nitrogen rather than to the heterocyclic ring via a carbonyl group as in the previous case. Condensation of p-chloroaniline with hexane-2,5-dione (or its dimethoxy-tetrahydrofuran equivalent) affords pyrrole 7. The acetic acid side chain is then elaborated as above. Thus, Mannich reaction leads to the dimethylaminomethyl derivative 8, which is in turn methylated (9) the quaternary nitrogen replaced by cyanide to afford 10. Hydrolysis of the nitrile then gives clopirac (11). 

KHC03, NaOAc, K2HP04, Na3P04, triethyl amine) and finally sodium carbonate was selected as the base of choice. Fluoride initiated Suzuki coupling with KF was unsuccessful. Dimethoxy ether was selected as the solvent after screening a variety of solvents (acetone, tetrahydrofuran, methanol, isopropyl alcohol, and methyl-i-butyl ether). 

Hydrogenate 47.5 g (I) in presence of 5 g Raney-Ni at room temperature and 1 atmosphere H2 with stirring (NaBH -Ni reduction described at start should also work). After absorption of 7.2 L H2 over two to three hours, filter and wash catalyst with 15 ml ethanol and evaporate in vacuum (or distill 77/20 for ethoxy compound, 53/22 for methoxy compound) to get 40 g 2,5-diethoxy (or dimethoxy)-tetrahydrofuran (II). 

Another representative example is the preparation of (3A,5/ ,7a/ )-5-(benzotriazol-l-yl)-3-phenyl[2,l-A oxazolopyr-rolidine 238 that was synthesized from benzotriazole, (A)-phenylglycinol, and 2,5-dimethoxy-tetrahydrofuran at room temperature. This reaction entailed the formation of two heterocyclic rings and two new chiral centers in one step (Equation 33) by double Robinson-Schopf condensation of the dialdehyde with the amino group and benzotriazole intercepting the initially formed iminium ion (Equation 36) <1999JOC1979>. 

Mono(2,6-dimethoxybenzoyl)tartaric acid Butanedioic acid, 2-[(2,6-dimethoxybenzoyl)oxy-3-hydroxy-, [R-(R, R )]- (12) (116212-44-3) 2,6-Dimethoxybenzoic acid Benzoic acid, 2,6-dimethoxy- (8,9) (1466-76-8) Trifluoroadetic anhydride Acetic acid, tritluoro-, anhydride (8,9) (407-25-0) Borane-Tetrahydrofuran Furan, tetrahydro-, compd. with borane (1 1) (8,9) (14044-65-6)... 

Menthyl isocyanopropanoate (5) has been alkylated by means of sodium hydride in tetrahydrofuran and subsequent addition of 3,4-dimethoxybenzyl bromide to give the product 6 in high yield115. The latter was transformed into a-methyl-(3,4-dimethoxy)benzylalanine hydrochloride (7, 85% overall yield from the propanoate) [a] 0 —0.8° (c = 7.5, CH3OH) mp 162-165 °C (decomp). The optically pure form has [a]p7 —8.8° (c = 0.84, CH3OH) and mp 169-171 °C (decomp). 

Als Losungsmitlel kann auch Methanol oder eine Benzol/Methanol-Mischung eingesetzt werden. Aceto-nitril, Tetrahydrofuran und 1,2-Dimethoxy-ethan sind dagegen ungeeignet. 

A review is given on the kinetics of the anionic polymerization of methyl methacrylate and tert.-butyl methacrylate in tetrahydrofuran and 1,2-dimethoxy-ethane, including major results of the author s laboratory. The Arrhenius plots for the propagation reaction+are linear and independent of the counterion (i.e. Na, Cs). The results are discussed assuming the active centre to be a contact ion pair with an enolate-like anion the counterion thus exhibiting little influence on the reactivity of the carbanion. 

Catalytic hydrogenation of 3,4-dihydro-2//-pyrimido[2,l-a]isoquinoline-2,4-diones (93) and 3,3-diethyl-9,10-dimethoxy-3,4,6,7-tetrahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione (94) over Pt02 and Pd/C catalysts gave l,3,4,6,7,llb-hexahydro-2/7-pyrimido[2,l-a]isoquinoline-2,4-diones (95) [69YZ649 71JPP71/09466]. From the mother liquid of compounds 93 (R = H, R1 = Et and R = R1 = Et) 3-ethyl-2-hydroxy-6,7-dihydro-and -8,9,10,1 l-tetrahydro-4//-pyrimido[2,l-a]isoquinolin-4-ones, and 3,3-diethyl-l,3,4,llb-tetrahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione, also could be isolated as minor products. Reduction of 3,3-diethyl-l,3,4,6,7,llfo-hexahydro-2//-pyrimido[2,l-a]isoquinoline-2,4-dione (95, R = R1 = Et, R2 = H) with LAH in tetrahydrofuran at 70°C for 9 h afforded 3,3-diethyl-l,3,4,6,7,llb-hexahydro-2//-pyrimido[2,l-a]isoquinoline (96). 

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