Hydroxyl groups, furans oxidation with

The hemiacetal hydroxyl group of the aldopyranosuloses 325 was usually protected in the form of the methyl glycoside by treatment with methyl orthoformate in the presence of a Lewis-acid catalyst.208 Higher yields of the corresponding methyl glycosides could be obtained by treatment of a glycopyranosulose with methyl iodide in the presence of silver oxide.211 One-step transformation of the dihydro-furan derivatives 324 into the methyl glycosides (326, 327) by treatment with methanol and formic or trifluoroacetic acid has been reported.212... 

The known adduct (385) of furan and vinylene carbonate, previously used for the synthesis of some cyclitols,256,257 has been transformed into DL-ribose derivatives. After hydroxylation of 385 and subsequent formation of the isopropylidene derivative, the carbonate group was removed by treatment with barium hydroxide, and the resulting diol was cleaved by oxidation with permanganate. Dicarboxyl-ic acid 386 gave, upon treatment with acetic anhydride, cyclic anhydride 387. The reaction of 387 with azidotrimethylsilane produced... 

A novel synthesis of the sesquiterpene ( )-cinnamodial (148) utilizes the furan ring as a latent 1,4-dialdehyde synthon (81JA3226). The triol (141) was thus oxidized to the ketofuran (142). Oxidation of the furan moiety with lead tetraacetate afforded a 90% yield of epimeric diacetates (143) which when exposed briefly to DBU gave dienone (144). Epoxidation of (144) and exposure of the epoxide (145) to p-toluenesulfonic acid gave the bis-acetal (146). Reduction of this intermediate to a diol and hydrolysis of the bis-acetal furnished dialdehyde (147). Acetylation of the secondary hydroxyl group completed the synthesis of cinnamodial (Scheme 32). 

Bicyclic furanes. French chemists have described the synthesis of the furanes (3) from (1) by epoxidation and rearrangement of the resulting oxides (2) with boron trifluoride etherate. Acetylation of the hydroxyl group blocks rearrangement to the furane. The paper includes a possible mechanism. 

Thiophene derivatives were also prepared from the respective furans 2 [37]. Thus, the 2,5-dihydroxymethyl thiophenes were obtained from 2 by reduction, protection of the hydroxyl groups, oxidation with m-chloroperbenzoic acid to the respective cis-hexenedione whose reduction with titanium trichloride and subsequent reaction with Lawesson reagent gave the protected thiophene derivative. 

The oxidation of alcohols to aldehydes or ketones by periodane has several advantages over chromium and DMSO-based oxidants because of its shorter reaction times, higher yields and simplified work up. There is very little overoxidation to the carboxylic acid. It is a practical reagent for the facile and efficient oxidation of benzylic and allylic alcohols. Saturated alcohols are slow in their reactions with it. It oxidizes alcohols in the presence of non-hydroxylic functional groups such as sulfides, enols, ethers, furans and 2°-amides. An example of the DMP oxidation is the oxidation of 3,4,5-trimethoxybenzyl alcohol (7.17) with 7.16 in CH2CI2 to give 94% yield of 3,4,5-trimethoxybenzaldehyde (7.18). 

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