Bailey-Liebeskind indole synthesis

Bailey-Liebeskind-O Shea Indoline-Indole Synthesis... 

Several applications of the Bailey-Liebeskind indoUne-indole synthesis are tabulated in Table 1 [5-8]. Entry 4 involves the generation of 8, 9, and 10 from dibromo compound 7, and Entry 5 involves the further Uthiation, of 10 to 11 (Scheme 2) [9]. Quenching of these species then afforded the products summarized in Table 1 (Entries 4 and 5). 

Bailey-Liebeskind-O Shea Indoline-Indole Synthesis 215 Table 1 Applications of the Bailey-Liebeskind Indoline-Indole Synthesis... 

Bailey and Liebeskind independently discovered the anionic cycUzation shown in Scheme 1 [1, 2] that leads to indoUnes and, by subsequent oxidation, to indoles. Both methods are virtually identical, involving bromine-lithium exchange followed by quenching of the aryllithium species with an electrophile (equations 1 and 4). The Af-allylindole can be deallylated with palladium (equation 2) [3], and the indohne is easily oxidized to the corresponding indole (equation 3). A selection of indoles prepared this way by Liebeskind and Zhang is shown (1-6) [2], The yields are overall for the two steps. These workers also employed chloranil (f-BuOMe, rt) to oxidize indohnes to indoles. An excellent review by Bailey and Mealy is available [4]. Bailey s related indoline synthesis via arynic cycUzation is presented in the later chapter on NucleophiUc CycUzation of Arynes (Chapter 65). 

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