1,1-Dialkoxy compounds

Acetals and Acylals. Acetals, which contain the group >C(OR)2, where R may be different, are named (1) as dialkoxy compounds or (2) by the name of the corresponding aldehyde or ketone followed by the name of the hydrocarbon radical(s) followed by the word acetal. For example, CH3—CH(0CH3)2 is named either (1) 1,1-dimethoxyethane or (2) acetaldehyde dimethyl acetal. 

No natural products or their analogues are included among the pyridopyridazines, but several interesting biologically active compounds have emerged. Some l-chloro-4-hydrazino- and 4-chloro-l-hydrazino-pyrido[2,3-d]pyridazines (460) are very active hypotensives, whilst related dialkoxy compounds have anticonvulsant activity (65CPB586). 

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). 

In the presence of base, alcohols and phenols add l,5-diphenylpenta-l,4-diyn-3-one (72JOU1398). At 40 °C addition occurs at both triple bonds to give a mixture of the 1,5-dialkoxy compound (411), the triketone and the pyran-4-one. On treatment with acid the former compounds are converted into the pyranone. However, at 15 °C only one triple bond is attacked giving the alkoxyvinyl ethynyl ketone (412), but this also forms the pyranone with acid (Scheme 136). 

A PNS effect involving anomeric stabilization of a geminal dialkoxy compound has been observed when comparing kinetic and thermodynamic data of reactions 55 and 56. Reaction 55... 

Diols can react with acyclic dialkoxy compounds to effect an exchange reaction (equation 86 ). 

Dialkoxy compounds react with several halogen-based electrophiles to give the corresponding halogenated compounds (equations 140 and 141 ). 

The dialkoxy compounds 3c and 3d both show hydrolysis rates comparable to their trifunctional counterparts 3a and 3b. Comparing the rate constants for 3-methacryloyloxy-propyltrimethoxy- and the difunctional 3-methacryloyloxypropyl(diraethoxy)methylsilane... 

Treatment of 2,4-dichloropyrido[3,2-t/]pyrimidine with sodium methoxide and ethoxide affords the corresponding 2,4-dialkoxy compounds.77 The 8-chloro substituent in methyl 2,4,8-trichloropyrido[3,2-if]pyrimidine-6-carboxyIate is unreactive towards sodium methoxide in methanol at room temperature449 or towards sodium benzylate,454 only the two chlorines in the 2,4-position being exchanged. This is a further confirmation of the reactivity order cited at the beginning of Section 7.2.2.2.1.5.4. 

The added acid most likely plays several roles. First, the acid is necessary for the redox transformation of Pd(0)-BQ to Pd(ll) + HQ in the catalytic cycle [65]. Second, the acid will lead to the formation of a cationic 7t-allylpalladium intermediate which will facilitate coordination of BQ. Third, the acid will protonate the oxygen of the coordinated BQ, and in this way the quinone becomes more electron-withdrawing. It was found that the rate of the reaction increased with the amount of acid, and that there was a linear increase in the range of 0-30 mol% of acid however, adding too much acid catalyzed the destruction of BQ. The stereochemistry of the dialkoxylation is consistent with a trans alkoxypalladation [118] of the diene to give 7t-allyl intermediate 91, followed by external trans attack of alcohol to give the cis-dialkoxy compound 92 (Scheme 11.32). 

Heating 3,4-bis(phenylsulfonyl)furoxan with a solution of sodium butoxide in butanol followed by reduction with trimethyl phosphite gives furazan 281 (Scheme 183). Compound 281 was converted into dialkoxy derivative 282 with the lithium salt of ( )-l-azabicyclo[2.2.2]octan-3-ol in 33% overall yield (96W012711, 97EUP773021, 98JMC379). 

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