Phenylfuran

The cycloaddition reactions of 2-phenyloxazol-4(5H)-one with acetylenic dipolarophiles has been briefly reported. " The formation of 2-phenylfurans may well involve a tautomerism analogous to that exhibited by azlactones (76 77). 

The catalytic asymmetric arylation (Heck reaction) of 2,3-dihydrofuran to give (/J)-2,3-di-hydro-2-phenylfuran which, upon Jones oxidation, yields (/ )- 2 (for assignment, see p 439)80. 

The assignment of (/ )-2,3-dihydro-2-phenylfuran rests on Jones oxidation which furnished (ft)-dihydro-5-phenyl-2(3//)-furanone [(/ )-24]80. The configuration of the corresponding S-enantiomer (obtained by yeast reduction of 4-oxo-4-phenylbutanoic acid) was established by correlation with ethyl (S)-3-hydroxy-3-phenylpropanoate (of known configuration, obtained itself by a baker s yeast reduction) by a sequence featuring an Arndt -Eistert homologization as the key step (see also p 403)19. 

Two furo-annelated benzo[c]furans, a benzo[2,l-Z) 3,4-c ]difuran (341) and a benzo[1.2-/ 3,4-c ]difuran (344) have been described. Acid-catalyzed ring closure of bisfuran 340, which is available from trans-trans-1,4-dibenzo-ylbutadiene (339) and /ranx-dibenzoylethylene. yields 341 in 83% yield. An independent synthesis which starts from 4-benzoyl-2-phenylfuran (343) is outlined in Scheme 21 the isomeric compound has been obtained similarly (Scheme 22). 

A very interesting fragmentation and isomerization has been discovered for 1-benzoylpyrazole (62)(88BSB945). FVP at ca. 800°C affords mainly 2-phenylfuran and phenylallene, as indicated by a real-time analysis using... 

Note that the two possible mechanisms can be distinguished by the position of the labeled atom in the 2-phenylfuran. 

Milkiewicz and coworkers [16] prepared a series of novel tetra-substituted furo[3,2-b Ipyrroles from the methyl or ethyl 3-bromo-2-phcnyllliro 3,2-/ pyrrole-5-carboxylate 40, which was prepared from 3-bromo-2-phenylfuran-2-carbaldehyde 39. The compounds 40 were subjected to a Suzuki coupling with 4-chlorophenyl boronic acid to form 41, which was treated with a variety of alkylating agents to afford the corresponding esters 42. The esters were then saponified to acids 43 (Scheme 6). 

As an extension of this work, photoinduced [2+2]-cycloadditions of 1-acetylisatin (13) with cyclic enolethers (furan, benzofuran, 2-phenylfuran, 8-methoxypsoralen), and acyclic enolethers (//-butyl vinyl ether and vinyl acetate) were investigated which afforded the spiro-oxetanes in high yields (82-96%) and with high regio- and diastereoselectivity (Sch. 4) [19]. Treatment of the furan-derived oxetane 15 with acid resulted in oxetane ring opening and yielded the 3-(furan-3-yl)indole derivative 16. 

The reduction of 2-phenylfuran to 4-phenylbutanol in glacial acetic acid with Pd/charcoal is very specific, in that the yield is nearly 80%1 8 ... 

Similar results were obtained with 2-phenylfuran. 

Nitropyridine 1-oxide reacts with l-cyano-2-phenylcthyne in refluxing toluene to form a 3-cyano-2-phenylfuran ring fused to the pyridine. 

Ultrasound-initiated tin hydride reduction of the allyl ether at 6l C and at — 55 °C, gives tetrahydro-4-methyl-2-phenylfuran in a trans/cis ratio of 87 13 and 94 6, respectively. The cyclization under thermal conditions (AIBN, 70 °C, 1 h) affords the products as a 79 21 mixture in 77% yield20. 

For 2-phenylfuran, electronic absorption spectra <84BCJ844> suggest a planar or nearly planar conformation as for 2,5-diphenylfuran, while for 2,4-diphenylfuran it should be more distorted than that of the monophenyl derivative. A theoretical analysis (ab initio level using a minimal basis set)... 

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