Furan diethers

A new family of furan diethers has been obtained by alkylation of 2,5-furandimetha-nol (Eq. 8) under the action of microwaves under PTC solvent-free conditions. 

The diethers were synthesized in high yield within short reaction times. When compared with classical heating, under otherwise comparable conditions, reactions times were improved by microwave activation. 

A series of new ethers has been obtained by alkylation of dianhydrohexitols (i. e. iso-sorbide, isomannide, isoidide) under the action of microwave irradiation and PTC conditions. Yields exceeded 90%, a dramatically improvement compared with those from conventional heating, despite similar temperature profiles. The best yields, for example from isosorbide, were obtained in the presence of a small amount of xylene and TBAB as catalyst at 140 °C (Eq. 9 and Tab. 5.6) [20], 

Poly ethers were next synthesized from isosorbide by means of a MW-assisted PTC method (Eq. 10). In addition to increasing the rate of the reaction, the MW affected the structure of the polymer (determined by MALDI/TOF mass spectrometry Tab. 5.7). Polymers of higher molecular weights, with ethylenic groups as chain terminations, were obtained conventional heating led to shorter hydroxylated compounds [21]. 

---

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],... 

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]. 

LeGoues FK, Hammar M, Reuter MC, Tromp RM, Majdoub M, Loupy A, Petit A, Roudesli S (1996) Coupling focused microwaves and solvent-free phase transfer catalysis application to the synthesis of new furanic diether. Tetrahedron 52 617-628... 

When solutions of 2,2-dimethyl-1,3-diphenylisoindene (467) were exposed to air at ambient temperature the products formed included l,3-diphenylbenzo[c]furan, acetone, an endoperoxide (468) and 1,2-dibenzoylbenzene (Scheme 120) (81JOC3752). The formation of l,3-diphenylbenzo[c]furan and acetone from the endoperoxide (468) may occur via the diether (469). 

Tetramethyl-la,2,3,4,6,7,8,8a-octahydrobenzofuro[4,3,2-fr,c,d]benzo-furan 604 was obtained in a one-pot reaction of 1 with lithium ethylenediamine(Li/EDA), through the enolization of dimedone in the alkaline medium to give the dienol, which underwent dehydration to the diether 602. The latter formed two free-radical sites at 2,2 -positions upon attack by the nascent hydrogen formed by Li/EDA, which led to the formation of a C-C bond to give the intermediate 603 that on isomerization furnished 604 (92IJC(B)762) (Scheme 128). 

---