Furan ring opening—indole ring closure: a new modification of the Reissert reaction for indole synthesis

Phenylfurylthieno[2,3-b]pyridyl-methanes. synthesis and reactions of the furan ring transformation

“…Consequently acyl protection of the amino group of compounds 1 was carried out before reduction of the carbonyl group. It is known [4,7] that such protection is also necessary at the following stage of alkylation of the furan by carbinols. The acylamino derivatives 2 were obtained in high yield (70-95%, Table 1) by boiling amino ketones 1 with the appropriate acid chlorides of carboxylic acids in dioxane or toluene by the procedure of [15] 1 а R = R 1 = Me, b R = CH 2 OMe, R 1 = Me, c R = R 1 = Ph, d R = 5-methyl-2-furyl, R 1 = Ph, e R = C 6 H 4 Br-4, R 1 = Ph; 2, 3 a-e R 2 = Ph, a R = R 1 = Me, b R = CH 2 OMe, R 1 = Me, c R = R 1 = Ph, d R = 5-methyl-2-furyl, R 1 = Ph, e R = C 6 H 4 Br-4, R 1 = Ph, f R = R 1 = Me,…”

“…Depending on the character of substituent X two routes of conversion are possible in principle: 1) closing of the hetero-or carbocycle between the furan and benzene rings with the formation of a product of type B [2,3] or 2) cleavage of the heterocycle and annelation of the benzene nucleus with the formation of a product of type C (Scheme 1). From the second route, named by us "furan ring opening -heterocyclic ring closing" [4], derivatives of benzofuran [5,6], indole [4,7], isochromone [8], isoquinolone [9,10], benzopyran [11], and cinnoline [12] were obtained. In particular, derivatives of indole of type C (Z = NTs) were synthesized by us starting from orthoacylaminoarenes D (Scheme 2), converted through carbinols E into compounds of type A (X = NHTs).…”

Opening of the furan ring in 2-R-amino- 3-furfurylthiophenes by the action of acids

“…The interest in this compound is explained by the fact that it can be regarded as a hetero analog of ortho-aminobenzophenones, which are used as starting compounds in the synthesis of derivatives of indole during the recyclization of benzylfurans [2][3][4]. By replacing the aromatic ketones by the heterocyclic analog it is possible to obtain derivatives of the condensed heterocyclic system thieno [2,3-b]pyrrole.…”

“…As for the aromatic analogs [2,3], we used the N-tosyl-substituted methanes 2a,e for the synthesis of the pyrrole derivative. The reaction of compounds 2a,e with the mixture of acids leads to opening of the furan ring accompanied by secondary cyclization, resulting in the formation of derivatives of thieno [2,3-b]pyrrole 5a,b.…”

Recyclization of tosylamino derivatives of 2-aryl-5-benzylfuran to give indoles through two alternative pathways

“…For many years, we have employed this property of furan compounds in the synthesis of benzo-fused heterocycles through the recyclization of ortho-substituted benzyl furans. In particular, we have reported that 2-(2-tosylaminobenzyl)furans under acid conditions are converted to indole derivatives [5][6][7] We have recently found that 2-alkyl-5-(2-tosylaminoaryl)furans under protolytic conditions also undergo recyclization and give indole derivatives [8]. However, in this case, furan, in contrast to 2-(2-tosylaminobenzyl)furans, may be seen as the formal equivalent of 1,3-dicarbonyl compounds.…”