Acetals from furan

Dimethylene-2,3-dihydrofuran derivatives, which are produced by fluoride-induced 1,4-conjugative elimination of trimethylsilyl acetate from the [(trimethylsilyl)methyl]-3-furan precursor 207, undergo subsequent [4-1-4] dimerization reactions to produce cycloocta[l,2-3 6,5-. ]difuran derivatives as a mixture of isomers (Equation 137) <1995JA841 >. A methyl substituent at the 3-methylene position was found to retard the rate of dimerization, an observation which is consistent with the proposed two-step mechanism involving the initial formation of a diradical intermediate in the rate-determining step (Table 16). 

Disubstituted furans can be prepared by the 3-lithiation of 2-phenylthio-5-alkylfurans, followed by reaction with an electrophile and then desulfurization with Raney nickel (Section 3.3.3.8.4). 3-Furylmercuri acetate can be obtained from furan-2-carboxylic acid (CHEC 3.11.3.9) and transformed to other 3-substituted furans via the lithio compound. 

Isobenzofuran-5,6-dicarboxaldehyde is available from furan-3,4-dicarboxaldehyde and 2,5-dimethoxytetrahydrofuran in acetic acid (mp 201-203°C) (87SUL99). 

To obtain the enantiopure products, we explored an alternative procedure again by employing lipase-mediated resolution.5 It is well known that a furfuryl alcohol furnishes a 3-pyrone hemiacetal on oxidative treatment.6 Actually, the reaction of (2-furfuryl)ethylene glycol 13, obtained7 from furan 10, with mCPBA afforded isolevoglucosenone8,9 (+)-15 having the opposite enone disposition to 1 after acid-cyclization of the pyrone 14. For enzymatic resolution, ( )-15 was converted into the alcohol ( )-16 and the acetate ( )-17, diastereoselectively (Scheme 3). 

Fig. 10. Dependence of solvent strength of B- or C-solvent (e) on its coverage of the surface (0) for amino-silica. Mixtures A/B or A/C, where A is hexane [data taken from Snyder and Schunk (/7)] O, CCl , CHjCla V, CHClatQ, ethyl acetate , tetrahydro-furan.

Aldehydes can be converted directly into 0,Se-acetals and used for radical cyclizations. This procedure is equivalent to a ketyl radical cyclization process, a typical example is shown in Eq. (13) [31]. Acetals such as 54 can also easily be converted into 0,Se-acetals by treatment with (z-Bu)2AlSePh. The selenide 55 is used for an efficient radical carbon-carbon bond formation [Eq. (14)1 [32]. A very reliable route to 0,Se-acetals from alcohols through the corresponding (tributylstannyl)methyl ethers has been used for the preparation of tetrahydro-furan derivatives [33]. 

Cationic cycloadditions. Ionization of p-benzoquinone monoacetals is induced by MejSiOTf in highly polar media (LiClO /EtOAc) and the carbocations are captured in situ by alkenes to give bicyclo[3.2.1]octene derivatives. A synthesis of 2-(l -phenylethoxy)-8-oxabicyclo[3.2.1]oct-6-en-3-one in good enantiomeric purity from furan and a mixed acetal of 2-(triethylsiloxy)acrolein (prepared from pyruvaldehyde dimethylacetal in three steps) is promoted by MejSiOTf. 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

Bromine/potassium acetate 2,5>Dialkoxydibydrofurans from furans... 

Saturated 1,4-diketones can suffer in this approach from the disadvantage that they can react with hydrazine in two ways, giving mixtures of the desired dihydropyridazine and an A -aminopyrrole this complication does not arise when unsaturated 1,4-diketones are employed.Synthons for unsaturated 1,4-diketones are available as cyclic acetals from the oxidation of furans (section 15.1.4), and react with hydrazines to give the fully aromatic pyridazines directly. ... 

An alternative route starts from furan (19). Reaction with bromine in methanol leads to 2,5-dimethoxy-2,5-dihydrofuran (20) which is transformed to but-2-ene-1,4-dial bisdimethyl-acetal (21). Double enol ether condensation with 1-propenyl methyl ether (22), followed by acetal hydrolysis and elimination, provides crystalline (all- -Cio-dialdehyde 8 in an overall yield >50% [13]. 

Palladous chloride cupric nitrate Acetals from ethylene derivatives 3,3-Dialkoxytetrahydro- from 2,5-dihydro-furans... 

In 2003, Kanerva s group reported the preparation of novel (l )-furyl-benzothiazole-based cyanohydrin acetates from the corresponding furan-... 

Bromine/potassium acetate 2,5-Dialkoxy-2,5-dihydrofuran from furan ring... 

Although cyanoacrylate polymers are most commonly prepared by anionic polymerization, they may also be prepared by free-radical polymerization using conventional radical initiators (36-38), provided adequate amounts of anionic polymerization inhibitors are employed. Bulk photoanionic polymerization of cyanoacrylates has also been described by a number of workers (39-43). These systems rely on the in situ generation of an anionic initiator from a neutral species, following absorption of light of an appropriate wavelength. The zwitterionic and radical copolymerization of cyanoacrylates has also been reported for a number of comonomers including vinyl ethers (44), ketene acetals (45), furan (46), vinyl ketones (47), and ethylene (48). 

Ammonium acetate Pyridine from furan ring 3-Hydroxy-2-aryipyridines... 

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