Furan, Amido

Furan, 2-alkenyl-3-hydroxytetrahydro-synthesis, 4, 677 Furan, alkyl-reactions, 4, 644 synthesis, 4, 710 Furan, 2-alkyl-mass spectra, 4, 21-22 synthesis, 4, 666 Furan, 3-alkyl-mass spectra, 4, 21-22 synthesis, 4, 665, 710 Furan, 5-alkyl-2-phenylthio-reactions, 4, 80 Furan, 2-alkyltetrahydro-synthesis, 4, 675, 711 Furan, 3-amido-synthesis, 4, 665 Furan, 2-amino-synthesis, 4, 74, 121, 661 tautomerism, 4, 38 Furan, 3-amino-tautomerism, 4, 38 Furan, 2-amino-3-cyano-synthesis, 4, 661, 689, 712 Furan, 3-amino-2-methyl-reaction, 4, 74 Furan, 2-aryl-reactions... 

Cycloaddition reactions of furans are still widely used as key steps in the construction of complex molecules including natural products. As an example, the intramolecular Diels-Alder cycloaddition of 2-amido substituted furans provides a useful tool for the synthesis of fused, nitrogen-containing poly-heterocycles. Thus, thermolysis of 3-substituted amidofuran produces tricyclic indolinone 39 as a 2 1 mixture of diastereomers via amidofuran cycloaddition-rearrangement methodology, which serves as a key intermediate in the total synthesis of ( )-dendrobine, a major component of the Chinese ornamental orchid Dendrobium nobile . 

The mixed metal alkyl-amido base [BuNa(TMEDA)][TMP2Mg] (TMP = 2,2,6,6-tetramethylpiperidine) is capable of deprotonating furan selectively at its 2-position in THF as a solvent. The product obtained is a complex tris-furylmagnesiate, with the empirical formula [Na2(THF)3][2-furyl6Mg2(TMEDA)] (15) . An X-ray crystal-structure determination showed that in the solid state this compound exists as a coordination polymer of [Na2(THF)3][2-furyl6Mg2] units linked by bridging TMEDA molecules (Figure 16). 

The aryl ketones 8 arise from an initially formed thietane followed by photochemical fission of the C-S bond and then by hydrolysis of an imine during chromatographic work-up <95JCS(P1)2931>. A 2-alkylation of a furan was effected by a vinylogous Pummerer reaction of the amido-substituted sulfoxide 9 <95JOC7082>. 

In the total synthesis of (-)-conocarpan, the chiral 2,3-dihydrobenzo[b furan core was constructed by radical based intramolecular cyclization as shown below <07CC2151>. In addition, chiral 2-isopropeny 1-2,3-dihydrobenzo[6J furans and 2-amido-bcnzo b furans were be made by palladium-catalyzed reaction in the presence of Trost ligand, and the rhodium(I)-catalyzed cyclization, respectively <07JOC2857 07OL2361>. 

PREPARATION AND DIELS-ALDER REACTION OF A 2-AMIDO SUBSTITUTED FURAN tert-BUTYL 3a-METHYL-5-OXO-2,3,3a,4,5,6-... 

A variety of 2-methylthio-5-amidofuran systems containing a tethered rc-bond on the amido nitrogen were prepared and utilized for a subsequent intramolecular Diels-Alder reaction (02JOC3412). Thus, exposure of imides 331 to DMTSF resulted in the formation of furans 332 in 40-70% yields (Scheme 62). Thermolysis of these furans in toluene at reflux initiated an intramolecular Diels-Alder reaction to first produce an intermediate oxabicyclo adduct. A subsequent fragmentation of the intermediate cycloadduct followed by a 1,2-thio shift provided the bicyclic amides 333 in good yields (ca. 70%). In an analogous manner, the cycloaddition chemistry of amidofurans 334 provided the azatricyclic products 335. Apparently, the rate of the 1,2-thio shift of the initially formed cycloadduct is much faster than the deprotonation/dehydration pathway previously described in Scheme 21. 

The Diels-Alder reaction of 2-amido substituted furans represents an excellent method for preparing substituted aniline derivatives, since these compounds are important starting materials for the preparation of various... 

Access to the initially formed but highly reactive oxabi-cyclic adduct by thermolysis of a 2-amido-substituted furan was considered to be desirable as it would provide a usefid ring system for further synthetic manipulation. This lability... 

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