Furans 1,4-dihalides

Reaction times were improved by microwave irradiation, and the same conditions were extrapolated to the synthesis of a series of new furanic diethers by alkylation of furfuryl alcohol by dihalides [83],... 

The other approach called upon phase-transfer catalysis (31). The potassium salt of 2,5-furandicarboxylic acid 11a was treated with primary aliphatic dihalides in a typical solid/liquid system in the presence of a crown ether. The resulting furanic-aliphatic polyesters had molecular weights of... 

NaOH solution of the diol and an organic solution of the dihalide in the presence of a phase-transfer catalyst (31). The best results were obtained with dichloro-p-xylene as comonomer and gave polymers with the furanic-aromatic structure 26 ... 

Pyridynes are also formed from ort/m-dihalides and alkali metals. Thus, reaction of 3-bromo-4-chloropyridine (889) with lithium amalgam and furan gives product (891) by trapping of the 3,4-pyridyne (890). Although 2,3-pyridyne is not formed from 3-halopyridines, because of the weaker acidity of the 2- as compared to the 4-hydrogen atom (see Section 3.2.1.8.2), it can be trapped by furan in small yield from the reaction of 3-bromo-2-chloropyridine with lithium amalgam. 

Diorgano tellurium dihalides, when refluxed with silver fluoride in toluene, tetrahydro-furan, or acetone, precipitate silver halides. The diorgano tellurium difluorides crystallize upon cooling the filtrate of the reaction mixture or evaporating the filtrate under vacuum. 

The moisture-sensitive complexes 215 and 217c have been prepared from dilithium perfluoropinacolate and the appropriate dihalide in tetrahydro-furan. One molecule of THF is also coordinated to the metal 64). 

Lithium telluride, prepared from tellurium and lithium triethylborohydride in tetrahydro-furan, and sodium telluride, obtained from sodium and tellurium in a dipolar, aprotic solvent or from tellurium - and Rongahte in aqueous sodium hydroxide reacted with aliphatic and aromatic dihalides to produce polymeric organo tellurium compounds. 

The process of homocoupling of aromatic halides by means of Ni and Pd was used successfully in the oligomerization or/and polymerization of 1,4-dichlorobenzene [89], 4,4 -dibromobiphenyl [90], and many other dihalides derived from furanes or pyr-idines [91]. Similarly, l,3-bis(chloromethyl) benzene led by this manner to poly-/ -xylene [92] through a novel pathway. 

Among the various derivatives of biomass, furan compounds obtained from furfural are important (200 000 t year ). A new family of furan diethers has been obtained by alkylation of 2,5-furandimethanol or furfuryl alcohol under the action of microwave irradiation with PTC solvent-free conditions (Scheme 10.79) [154]. Reaction times were improved by use of microwave irradiation, and the same conditions were extrapolated to the synthesis of a series of new furan diethers by alkylation of furfuryl alcohol by dihalides. 1,4-Diketones substituted by furans or thiophenes were synthesized by conjugate addition of aldehydes to a,j8-unsaturated ketones by irradiation without solvent in the presence of thiazolium halides and DBU adsorbed on alumina [155]. 

Bis(cyclopentadienyl) complexes CP2M (M = Ge, Sn, Pb) have been prepared by reaction of cyclopentadienylsodium and an appropriate dihalide in tetrahydro-furan. Electron diffraction shows that in the vapour these molecules have angular structures on account of the electron pair on the metal. In the solid state the germanium compound polymerizes within 3 h at ambient temperature, the tin compound within five days. The cyclopentadienyl groups are coordinated in a symmetrical pentahapto fashion (p. 191). Association through the rings occurs in the crystalline lead compound to give a polymeric chain structure (Fig. 4.8). 

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