2- furan, reaction with ethyl

Among the less widely exploited interconversion processes are those involving thermal reactions with ethyl azidoformate, which convert furan into A-ethoxycarbonyl-A -pyrrolin-2-one, and thiophenes into A-ethoxycarbonylpyrroles (Scheme 96a) (64TL2185). The boron trifluoride catalyzed reaction of l,3-diphenylbenzo[c]furan with A-sulfinylaniline results in the replacement of the oxygen by an iV-phenyl group (Scheme 96b) 63JOC2464). 

The reaction with ethyl acetoacetate has been extended to glycolaldehyde, and to carbohydrates other than n-glucose, by employing different experimental conditions it is probably applicable to aldoses in general. With d-fructose, yields are lower, but two molar proportions of water are liberated and a crystalline product results. This has a constitution similar to that of II but with the D-omhfno-tetrahydroxybutyl chain at the /3-position on the furan ring. The reaction has been applied successfully to other ketoses and... 

Vinylbenzo[7]furans, 3-vinylfuropyridines, and 3-vinylindoles were employed as conjugated dienes in the Diels-Alder reaction with ethyl acrylate, affording tricyclic adducts in fair to good yields, as shown in Equation (103) <20020L2791>. 

Formyl and 2-acetylfuran underwent an unusual reaction with ethyl azodicarboxylate to form adducts 285 and 286, respectively, as depicted in Equation (177) <1997T9313, 1999J(P1)73>. Computational studies of the reaction suggested an initial Diels-Alder reaction between the furan and azodicarboxylate, followed by rearrangement of the cycloadducts. A similar transformation was observed for the reaction between furfurals and 1,4-phthalazinedione in the presence of Pb(OAc)4, as shown in Equation (178) <20020L773>. 

Electron-rich heterocycles such as furans and pyrroles undergo facile reactions. The furan 20 is an active compound and the reaction with ethyl phenylpropio-late (21) proceeded at room temperature in dichloromethane in the presence of AcOH, instead of TEA, to give rise to (Z)-2-alkenylfuran 22 exclusively [8]. The 3-alkenylpyrrole 24 was obtained by the reaction of the trisubstituted pyrrole 23 with 21 [9]. 

The high reactivity of pyrroles to electrophiles is similar to that of arylamines and is a reflection of the mesomeric release of electrons from nitrogen to ring carbons. Reactions with electrophilic reagents may result in addition rather than substitution. Thus furan reacts with acetyl nitrate to give a 2,5-adduct (33) and in a similar fashion an adduct (34) is obtained from the reaction of ethyl vinyl ether with hydrogen bromide. 

Syntheses of trisubstituted furans are much less common than the disubstituted derivatives only one 2,4-disubstituted 3-furoate has been prepared using the Feist-Benary reaction. Combination of chloroacetone (4) with ethyl acetoacetate (9) provides ethyl 2,4-dimethyl-3-furoate (28) in 54-57% yield. The procedure for this... 

The pyranofurooxazoline 109 can be prepared by a nitrene insertion reaction of the corresponding furan 110 upon treatment with ethyl azidoformate at — 50 °C under photolysis conditions. Compound 109 is moisture sensitive, and upon treatment with wet acidic THF was converted quantitatively to the more polar furanopyran 111. The structure and stereochemistry of 109 were proved unambiguously by X-ray diffraction, showing that the nitrene inserted anti to the bridgehead methyl group <1999JOC736> (Scheme 30). 

If the data obtained on the dehydration of the 2-(aWo-polyhydroxy-alkyl)benzimidazoles31 is considered, it is to be expected that no inversion occurs in the configuration of the carbon atom next to the furan ring. If this is so, the anhydride should have formula XXXIV. With the object of deciding this question, researches are being carried out32 on the reaction of ethyl acetoacetate with 3,6-anhydro-n-glucose and with D-altrose. 

The reactions of heteroaromatic compounds such as furans, pyrroles, and indoles with alkynoates proceed under very mild conditions (in acetic acid or even in neutral solvents such as CH2C12 at room temperature). For example, the reaction of pyrrole with ethyl phenylpropiolate gives the 2-alkenylated pyrrole (Equation (44)).47c This reaction is applied to the direct synthesis of a /3-alkenylpyrrole, the pyrrole fragment of haemin (Equation (45)).47d The present reaction provides a very convenient method for functionalization of arenes and heteroarenes. 

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. 

Other rings have been fused onto thieno[2,3-f]pyridazines. The reaction of 48 with ethyl chloroacetate provides a fused furan derivative 49 (Equation 19) <1999M1117>. 

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