Furan, 2- preparation

Functionalized hexanofuran shown below was provided as a 5.1 1 mixture of the desired diastereomer and its epimer by Pd-catalyzed cyclization of 3-iodo-4-substituted furan prepared from 3,4-diiodofuran through I-Li exchange, and was followed by trapping of the lithiated furan with an aldehyde. The modification of this procedure to produce diiodofuran using 1-methyl-2-pyrrolidinone as co-solvent was also reported <06JA17057>. 

The preparation of furans by acid catalyzed dehydration of 1,4-diketones followed by cyclization of the monoenol has been comprehensively reviewed (69RCR389). This method of furan preparation is useful for all 1,4-diketones which are not sterically hindered with the highly hindered l,4-bis(2,4,6-triisopropylphenyl)-l,4-butanedione no cyclization occurs (50JA5754). Although sulfuric acid is normally used for cyclization, hydrochloric acid was employed in the conversion of a 1,2-diacylethylene to a furylacrylic acid derivative (59MIP31200). Other reagents used for this purpose include polyphosphoric acid, phosphorus trichloride, zinc chloride and DMSO. Both DMSO and phosphoric esters provide neutral... 

As in all catalytic reductions, the purity of the starting material is of great importance. Redistilled furan, b.p. 31-32 , prepared by the method of Wilson (Org. Syn. Coll. Vol. i, 269) is quite satisfactory. It has been reported that furan prepared by the method of Gilman and Louisinian should be dried over calcium chloride and fractionated carefully. It is advisable to redistil the furan shortly before use and to avoid contact with rubber stoppers. 

DimetaHation of Furan. Preparation of 2,5-bis(Methy]thio)Furan... 

---