Furan free radical attack

The reactions of free radicals with furan and its derivatives can give both addition and substitution products depending on the specific system (11-13). With 2-substituted furans, the attack takes place predominantly at C5 and leads, by additon, to the corresponding furyl radicals which must be viewed as relatively stabilized interemediates because of the dienic-aromatic character of the furan heterocycle. These premises are essential to the understanding of the varied responses of furan monomers to free-radical activation. 

The copolymerization of furan and 2-methylfuran with dienophiles such as maleic anhydride leads to polymer structures with furan pendent functionality. Furan, 2-methylfuran, and 2,5-dimethylfuran have been copolymerized with acrylic monomers (51,52) and acrylonitrile (52,53). The furan ring of furan, 2-methylfuran, and 2,5-dimethylfuran participates as a diene in a free radical copolymerization with acrylonitrile. The initial step for furan and for 2,5-dimethylfuran is the attachment of an acrylonitrile radical at the 2-position, but for 2-methylfuran, the attack is at the-5-position. Propagation proceeds by the attack of the furan radical on an acrylonitrile molecule, to leave one olefinic bond in the structure derived from the furan ring. If this bond is in the 4,5- or 2,3-position, it may be involved in a second additional reaction by the return of the propagating chain. 

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). 

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