Furan, acetoxylation

Acetoxylation. Although furans are readily oxidized, furans substituted by a triisopropylsilyl (TIPS) group when treated with DDQ in toluene-acetic acid at 0° undergo acetoxylation at an adjacent a-methylene group.3... 

Diacetoxylation of 1,3-butadiene is a process that drew much attention since the product l,4-diacetoxy-2-butene may be converted to 1,4-butanediol and tetrahydro-furan by further transformations (see Section 9.5.2). The liquid-phase acetoxylation of 1,3-butadiene in a Wacker-type system yields isomeric 1,2- and cis- and trans-1,4-diacetoxybutenes ... 

Lead tetraacetate in glacial acetic acid is used for 2,5-acetoxylation of furan derivatives272 ... 

As usual a cis-trana isomeric mixture forms, which can be separated by crystallization. 3-Isopropylfuran can be oxidized in a similar way, while 2-substituted furans are resistant to acetoxylation.273... 

Anodic acetoxylation of furan can be done in acetic acid containing acetate [173, 174] and benzoyloxylation in DMF containing benzoic acid and lithium chloride [175]. A mixture of cis- and ra 5-benzoyloxylated product is formed. Cyanomethoxylation of 2,5-dimethylfuran gives a mixture of cis- and rmn5-2-cyano-5-methoxy-2,5-dimethyldihydro-furan [176-178]. 

The anodic oxidation of furans in methanol was also carried out without an intentionally added electrolyte (Figure 12.11) [38, 39]. 2,5-Dimethoxy-2,5-dihydro-furan was obtained in 98% yield. The anodic methoxylation and acetoxylation of various organic compounds was also achieved using this system. 

Different electro-organic reaction systems have been studied. The anodic reactions investigated are mainly the four-electron methoxylation of 4-methoxytoluene [6, 7, 11, 12] and the two-electron methoxylation of furan to 2,5-dimethoxy-2,5-dihydrofuran [10], but also other methoxylation and acetoxylation reactions [11]. Methoxylation reactions are performed in methanol as a solvent, whereas acetoxyla-tions are performed in acetic add. Moreover, Kiipper et al. [7] reported the anodic two-electron decarboxylation of sodium glucanate in an aqueous medium. The cathodic... 

Electrochemical oxidation of fiirans can also been carried out without intentionally added electrolyte using a microflow system. I n this case, an electrochemical thin-layer flow cell, which has a simple geometry with a glassy carbon anode and a platinum cathode directly facing each other at a distance of 80 pm apart is used (Figure 7.9) [65, 66]. 2,5-Dimethoxy-2,5-dihydrofuran is obtained in 98% yield by the oxidation of furan in methanol solvent. Similar electrochemical methoxylation and acetoxylation of various organic molecules can also be carried out using this system. 

---