A novel synthesis of indole derivatives via a claisen rearrangement

New Variation of the Aromatic ortho-Claisen Rearrangement: Synthesis of Fused Thiophenes and Pyrroles

“…50 During this investigation, we observed the formation of an unusual product 94 (Scheme 31). 39,40 however, the nucleophilic attack by the mchlorobenzoate moiety on 97 to give the expected product 95 did not occur in this instance. The major product (iso-lated) was the bis-indole derivative 94.…”

“…In a continuing effort to exploit this novel finding to obtain other heterocycles, Majumdar and Thyagarajan 14,18 described an extension of their finding to nitrogen analogues for construction of the five-membered pyrrole ring of 2,3-disubstituted indoles. 39 It is relevant to mention that both the sulfoxide and amine oxide rearrangements proceed through the occurrence of concomitant [ Whilst the sulfoxides rearrange in refluxing carbon tetrachloride or dichloromethane, the corresponding rearrangement of the amine oxides occurs more readily, and the nitrogen heterocycles are obtained in almost quantitative yields. The intermediacy of [2,3]-and [3,3]-sigmatropic rearrangements in this process results in negligible charge build up in the aromatic ring and the reaction was found to proceed with extreme facility, even in the presence of electron-withdrawing groups.…”

“…Majumdar and Thyagarajan 14,18 described an extension of their finding to nitrogen analogues for construction of the five-membered pyrrole ring of 2,3-disubstituted indoles. 39 It is relevant to mention that both the sulfoxide and amine oxide rearrangements proceed through the occurrence of concomitant [2,3]-and [3,3]-sigmatropic rearrangements. Thus, the synthesis 39,40 Whilst the sulfoxides rearrange in refluxing carbon tetrachloride or dichloromethane, the corresponding rearrangement of the amine oxides occurs more readily, and the nitrogen heterocycles are obtained in almost quantitative yields.…”

“…39 It is relevant to mention that both the sulfoxide and amine oxide rearrangements proceed through the occurrence of concomitant [2,3]-and [3,3]-sigmatropic rearrangements. Thus, the synthesis 39,40 Whilst the sulfoxides rearrange in refluxing carbon tetrachloride or dichloromethane, the corresponding rearrangement of the amine oxides occurs more readily, and the nitrogen heterocycles are obtained in almost quantitative yields. The intermediacy of [2,3]-and [3,3]-sigmatropic rearrangements in this process results in negligible charge build up in the aromatic ring and the reaction was found to proceed with extreme facility, even in the presence of electron-withdrawing groups.…”

A Tribute to Prof. B. S. Thyagarajan

“…Substituting an Nor S-oxide for one of the oxygens of the butynyl bis(aryl ether) compounds illustrated below led to useful indole 22 or benzothiophene 23 derivatives, respectively (scheme 10). It is of interest to compare and contrast various mechanistic possibilities that can be offered to account for the course of the reactions shown therein.…”