Fused furans from

AryT3,4-fused furans 63 are synthesized in moderate to good yields from propargyl nucleophiles and a-sulfonyl a,p-unsaturated ketones under palladium catalysis conditions... 

There are several reports of tetrahydroisoquinolines with a fused furan ring that could be argued (for the sake of the classification used in this collection) as an oxidative attack by the a-hydrogen of the 1-benzyl onto the 8-HO substituent, in a manner similar to the formation of a seven-membered ether ring seen in the cularines. It can also be seen as a similar oxidative attack from an a-hydroxy group (a commonly encountered benzyl substituent) on the 8-hydrogen position. The first of these two mechanisms (illustrated above) is used in this collection. 

Formation of fused heterocycles from acetylenic or allenic sulfones and pyrroles or furans as dienes 01T5263. 

The fast fade rate shown by 2-(4-trifluoromethyl)-2-phenyl-5-trifluorophenyl-[l]benzofuran[2,3-(]naphtho[l,2-6]pyran is attributable to the bulky 5-substituent rather than to the fused benzofuran ring <01WOP36424>. Its synthesis follows from the preparation of 9-hydroxy-7-trifluoromethylbenzo[6]naphtho[ f]furan from 4-chloromethyldibenzofuran (Scheme 18). 

The transition state with the highest Bond Order Deviation (BOD) also has a higher energy. From the example of cyclopropene addition to benzo-fused furans, we can perfectly demonstrate this approach. The BOD for both exo and endo transition state structures of cyclopropene addition to benzo[6]furan were higher than for addition to benzo[c]furan (Table 24). On the other hand, the transition... 

S.2.2.7. Fused Heterocycles from Cyclic Dipolarophiles. Furan provides a useful example of a diene acting instead as a dipolarophile. As will be discussed in Chapter 6, this molecule has the lowest aromaticity of the 5-membered heterocycles. It is also useful as a diene in Diels-Alder cycloadditions, but here we will observe that one double bond can react with a 1,3-dipole (Scheme 5.34). 

Next, Gevorgyan et al. disclosed an alternative route to tetrasubstituted and even fused furans via a transition metal-catalyzed migratory cydoisomerization of skipped propargylic systems. Thus, syntheses of 3-acyloxyfurans 69 from alkynyl acetates 68 occurred with a formal 1,2-migration in the presence of 5 mol% of Ag-catalyst at room temperature (Scheme 8.28) [139,140[. Several other transition metals such as Cu(II),... 

The Formation of Fused Furan Rings via Tandem P-Fragmentation-Cyclization of Cyclobutanoxyl Radicals Generated from [2- -2]-Photoadducts Derived from 4-Flydroxycoumarin, 3-(or 4-)-Hydroxy-quinolinone or 2-Hydroxynaphthoquinone withA alkenes... 

Chemistry of conjugated heterocycles built from furan pyrrole, or thiophene ring fused with bicyclic (norbomadiene, bomene, or azanorbomene) skeletons 98YGK192. 

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