Furan reaction with acetone

Figure 6-4. The formation of a macrocycle from the reaction of acetone with furan. This provides a rare example of a high-yield, cyclisation which occurs at normal concentrations of the reactants. In fact, considerable care needs to be taken with this reaction, which may be explosive ...

The first naphtho[a]cyclopropene 68d was also obtained by that route. 3H-indazole was proposed as an intermediate in this reaction 78>. The reaction proceeds equally well from the triplet state of 7. However with acetone light capture from the sensitizer may not have been complete. A trapping of the diradical intermediate 67 to give the known indene 69 by photolysing 7 in dimethyl-acetylene-dicarboxylate (ADC) afforded only a trace of 69. However the yield of 68a was reduced to 40%. Either trapping of 67 was not effective enough or ADC may have acted as quencher. Trapping with furan or cyclopentadiene was also not effective 78a). 

The reaction is best carried out using the Meerwein reaction conditions (acetone-water/CuCl2). Analogous reactions were described for diazoarsanilic acid and furan.160 The course of the reaction with 2-furylacrylic acid is more complex, as decarboxylation occurs and diarylated compounds form161 ... 

On the other hand, Gavrilova and Gonikberg opened the furan ring with hydrogen, without the use of catalysts.213 The reaction is carried out at high temperature (350-375°) and at a pressure between 240 and 750 atmospheres, in the absence of a solvent. The following products are obtained from 2-methylfuran acetone, methyl ethyl ketone, methyl butyl ketone, methyl amyl ketone, acetophenone, methylpropylcarbinol, w-pentane, and water. The authors suggest that these products are formed by a free radical mechanism. 

The parent calix[8]furan was formed in traces in a BF3 Et20 induced reaction of L3 25, difuryl methane and CH2(OMe)2 (94JCS(P1)2881). HCl induced cyclization of L4 9 (R = Me) with acetone gave Cg 31 in low yield along with major product C4 4 (85JCS(P1)973). The availability of Eg 9 (R = Me) (2001JCS(P1)3297) now could facilitate its formation. 

Early applications of iron cationic species resulted from the facile reaction of a, a -dibromo-(and tetrabromo) acetone with Fe2(CO)9 with formation of the cation (A). Such cationic complexes can be efficiently trapped by olefin with formation of five-membered ketones. The reaction with conjugated dienes affords a straightforward access to tropones. Furan is a particularly good acceptor of these cationic complexes whereas their addition to enamines constitutes a potentially useful pathway to prostaglandins (cyclopentenones being thus obtained). 

The double furan 140 [173] [obtained in one step from 2,4-dimethylfuran (prepared in three steps from acetone) by reaction with acetaldehyde] adds to... 

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