22793-63-1Relevant articles and documents
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Witkop et al.
, p. 2641,2646 (1951)
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Direct Synthesis of Indoles from Azoarenes and Ketones with Bis(neopentylglycolato)diboron Using 4,4′-Bipyridyl as an Organocatalyst
Misal Castro, Luis C.,Sultan, Ibrahim,Nishi, Kohei,Tsurugi, Hayato,Mashima, Kazushi
, p. 3287 - 3299 (2021/03/01)
Multifunctionalized indole derivatives were prepared by reducing azoarenes in the presence of ketones and bis(neopentylglycolato)diboron (B2nep2) with a catalytic amount of 4,4′-bipyridyl under neutral reaction conditions, where 4,4′-bipyridyl acted as an organocatalyst to activate the B-B bond of B2nep2 and form N,N′-diboryl-1,2-diarylhydrazines as key intermediates. Further reaction of N,N′-diboryl-1,2-diarylhydrazines with ketones afforded N-vinyl-1,2-diarylhydrazines, which rearranged to the corresponding indoles via the Fischer indole mechanism. This organocatalytic system was applied to diverse alkyl cyclic ketones, dialkyl, and alkyl/aryl ketones, including heteroatoms. Methyl alkyl ketones gave the corresponding 2-methyl-3-substituted indoles in a regioselective manner. This protocol allowed us to expand the preparation of indoles having high compatibility with not only electron-donating and electron-withdrawing groups but also N- and O-protecting functional groups.
Catalytic Asymmetric N-Alkylation of Indoles and Carbazoles through 1,6-Conjugate Addition of Aza-para-quinone Methides
Chen, Min,Sun, Jianwei
supporting information, p. 4583 - 4587 (2017/04/11)
Catalytic asymmetric N-alkylation of indoles and carbazoles represents a family of important but underdeveloped reactions. Herein, we describe a new organocatalytic strategy in which in situ generated aza-para-quinone methides are employed as the alkylating reagent. With the proper choice of a chiral phosphoric acid and an N-protective group, the intermolecular C?N bond formation with various indole and carbazole nucleophiles proceeded efficiently under mild conditions with excellent enantioselectivity and functional-group compatibility. Control experiments and kinetic studies provided important insight into the reaction mechanism.
Aqueous Titanium Trichloride Promoted Reductive Cyclization of o-Nitrostyrenes to Indoles: Development and Application to the Synthesis of Rizatriptan and Aspidospermidine
Tong, Shuo,Xu, Zhengren,Mamboury, Mathias,Wang, Qian,Zhu, Jieping
supporting information, p. 11809 - 11812 (2015/10/05)
Treatment of o-nitrostyrenes with aqueous TiCl3 solution at room temperature afforded indoles through a formal reductive C(sp2)-H amination process. A range of functions such as halides (Cl, Br), carbonyl (ester, carbamate), cyano, hydroxy, and amino groups were tolerated. From β,β-disubstituted o-nitrostyrenes, 2,3-disubstituted indoles were formed by a domino reduction/cyclization/migration process. Mild conditions, simple experimental procedure, ready accessibility of the starting materials and good to excellent yields characterize the present transformation. The methodology was used as a key step in a concise synthesis of rizatriptan and a formal total synthesis of aspidospermidine. Mild and efficient treatment of o-nitrostyrenes with aqueous TiCl3 solution at room temperature afforded indoles through a formal reductive C(sp2)-Hamination process. A concise synthesis of a marketed drug (rizatriptan) and a formal total synthesis of aspidospermidine featuring this novel N-heterocyclization process are reported.