Furan 2- acetate, formation

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Mercury(II) acetate tends to mercurate all the free nuclear positions in pyrrole, furan and thiophene to give derivatives of type (74). The acetoxymercuration of thiophene has been estimated to proceed ca. 10 times faster than that of benzene. Mercuration of rings with deactivating substituents such as ethoxycarbonyl and nitro is still possible with this reagent, as shown by the formation of compounds (75) and (76). Mercury(II) chloride is a milder mercurating agent, as illustrated by the chloromercuration of thiophene to give either the 2- or 2,5-disubstituted product (Scheme 25). 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

Esters of diphenylacetic acids with derivatives of ethanol-amine show mainly the antispasmodic component of the atropine complex of biologic activities. As such they find use in treatment of the resolution of various spastic conditions such as, for example, gastrointestinal spasms. The prototype in this series, adiphenine (47), is obtained by treatment of diphenyl acetyl chloride with diethylaminoethanol. A somewhat more complex basic side chain is accessible by an interesting rearrangement. Reductive amination of furfural (42) results in reduction of the heterocyclic ring as well and formation of the aminomethyltetrahydro-furan (43). Treatment of this ether with hydrogen bromide in acetic acid leads to the hydroxypiperidine (45), possibly by the intermediacy of a carbonium ion such as 44. Acylation of the alcohol with diphenylacetyl chloride gives piperidolate (46). ... 

This rearrangement of allylic acetals can also be used for furan annelations, in which the formation of the new tetrahydrofuran ring is coupled with ring enlargement of the starting ring.3 The same dr-fused bicyclic tetrahydrofuran is formed from either one of the cis- or mwr-allylic diols used as starting materials. 

Intramolecular alkoxycarbonylation of alkynols is parallel to what has been described for alkenols except that functionalization of the triplebond produces a double bond. No lactone formation is observed in the Pd(II)-catalyzed oxidative cyclization-carbonylation of alkynes. Instead [(methoxycarbonyl)methylene]tetrahydrofurans are selectively formed [134, 135]. Moreover, starting from an enynol, furan-2-acetic ester is obtained resulting from a final aromatization step [136]. 

Diketone 829 closely parallels 820 in its chemical reactivity. Introduction of a functionalized bridging carbon can be achieved with ethyl formate and base . The acetate group in 8JO 6 is remarkably easily replaced with retention by simple nucleophiles, e.g, the conversion to 8JI. The implicated peristyl-3-ene-2,6-dione (8J2) can in fact be obtained as a colorless crystalline compound. Also, 8J0a spontaneously dehydrates during ketalization to produce 8JJ. The strained double bond in 832 enters readily into Diels-Alder reaction with furan to furnish a 3 1 mixture of 834a and 834b. 

Wenkert and Khatuya (51) examined the competition between direct insertion of a carbene into furan (via cyclopropanation) and ylide formation with reactive side-chain functionality such as esters, aldehydes, and acetals. They demonstrated the ease of formation of aldehyde derived carbonyl ylides (Scheme 4.30) as opposed to reaction with the electron-rich olefin of the furan. Treatment of 3-furfural (136) with ethyl diazoacetate (EDA) and rhodium acetate led to formation of ylide 137, followed by trapping with a second molecule of furfural to give the acetal 138 as an equal mixture of isomers at the acetal hydrogen position. 

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). 

Evidence for the formation of furans is found in the results of treatment of D-glucal (58) either with dilute acetic acid or with 25 mM ethanolic sulfuric acid for 10 minutes at 70°, to produce80 the optically active 2-(l>g(ycero-l,2-dihydroxyethyl)furan (60), presumably by way of the 2-ene 59. This compound is also produced from 3,6-anhy-... 

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