TheN-tert-Butylcarbamoyl Directed Metalation Group for the Regiospecific Synthesis of 2-Substituted Pyrroles and Indoles

The Synthesis and Applications of Heterocyclic Boronic Acids

“…A major limitation to this approach is the known tendancy of 1-(phenylsulfonyl)pyrrole (44) to undergo competitive desulfonylation when attempting to effect a C-2 lithiation reaction. 67,68 The authors were unable to avoid this serious side reaction and were only able to obtain the corresponding acid 45 in very low yield. They did report, however, that the corresponding Suzuki coupling reaction took place efficiently in yields ranging from 39-91% without the concommitant deboronation reaction highlighted above.…”

Metalated Indoles, Indazoles, Benzimidazoles, and Azaindoles and Their Synthetic Applications

“…In order to facilitate removal of the protecting group, other nitrogen-protecting groups, such as tert-butoxycarbonyl (Boc) 23 and lithium carboxylate 24 have frequently been employed. Other, less common protecting groups are also available: trimethylsilyl, (trimethylsilyl)ethoxymethyl, 25 dialkylaminomethyl, 26 diethoxymethyl, 27 tert-butylaminocarbonyl, 28 dihydrooxazol-2-yl, 29 methoxymethyl, 30 methoxy, methoxymethoxy, 31 and 4-methoxyphenyl. 30d The 2-lithiated species can be subsequently trapped with various electrophiles to give 2-substituted indole derivatives.…”

Structural Reorganization of Allyl Isothiocyanate into Pyrrole Ring under Superbase­: A Straightforward Access to NH-2-(Alkylsulfanyl)-1H-pyrroles and N-Alkyl-2-(alkylsulfanyl)-1H-pyrroles

“…The yields of the pyrrole derivatives 6 are not very high, but it should be pointed out that our direct method is preferred over the multistep route for NH-2-substituted pyrroles, which involves N-protection of the pyrrole, treatment of the Nprotected compound with two equivalents of n-BuLi, reaction with an electrophilic reagent at the 2-position, and deprotection. 14 At least pyrroles 6c and 6d can also be obtained in moderate to good yields without the use of water before alkylation. For this, one equivalent of the corresponding alkyl iodide was added dropwise to the reaction mixture (method B) (Scheme 3).…”