AsymmetricN-Allylation of Indoles Through the Iridium-Catalyzed Allylic Alkylation/Oxidation of Indolines

Selective Iron Catalyzed Synthesis of N-Alkylated Indolines and Indoles

Whereas iron catalysts usually promote catalyzed C3-alkylation of indole derivatives via a borrowing-hydrogen methodology using alcohols as the electrophilic partners, this contribution shows how to switch the selectivity towards N-alkylation. Thus, starting from indoline derivatives, N-alkylation was efficiently performed using a tricarbonyl(cyclopentadienone) iron complex as the catalyst in trifluoroethanol in the presence of alcohols leading to the corresponding N-alkylated indoline derivatives in 31-99 % yields (28 examples). The one-pot, two-step strategy for the selective N-alkylation of indolines is completed by an oxidation to give the corresponding N-alkylated indoles in 31-90 % yields (15 examples). This unprecedented oxidation methodology involves an iron salt catalyst associated with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and a stoichiometric amount of t-BuOOH at room temperature.

Sequential Metal Catalysis towards 7-Oxostaurosporine and Its Non-Natural Septanose Analogue

We report sequential metal catalysis towards indolocarbazole glycosides. The signature event is highlighted by i) Pd⁰ -catalyzed addition of indolocarbazole to alkoxyallene combined with ring-closing-metathesis; ii) Ru-catalyzed chemoselective olefin migration; iii) Pd^II -catalyzed oxidative cyclization to build the bicyclic core structure of the target compounds. This approach gave access to both natural pyranose- and non-natural septanose glycosides. A short formal synthesis of 7-oxostaurosporine was achieved via this strategy.

Rhodium-Catalyzed Chemodivergent Regio- and Enantioselective Allylic Alkylation of Indoles

The control of C3/N1 chemoselectivity in indole alkylation with the same electrophiles is still challenging. An Rh/bisoxazolinephosphane-catalyzed chemodivergent regio- and enantioselective allylic alkylation of indoles was developed. Chiral C3- and N1-allylindoles can be selectively obtained with high branched/linear ratio and up to 99 % ee by changing the counteranion of Rh, the allylic carbonate, the reaction temperature, and the ligand.

Iridium-Catalyzed Enantioselective Intermolecular Indole C2-Allylation

The enantioselective intermolecular C2-allylation of 3-substituted indoles is reported for the first time. This directing group-free approach relies on a chiral Ir-(P, olefin) complex and Mg(ClO4 )2 Lewis acid catalyst system to promote allylic substitution, providing the C2-allylated products in typically high yields (40-99 %) and enantioselectivities (83-99 % ee) with excellent regiocontrol. Experimental studies and DFT calculations suggest that the reaction proceeds via direct C2-allylation, rather than C3-allylation followed by in situ migration. Steric congestion at the indole-C3 position and improved π-π stacking interactions have been identified as major contributors to the C2-selectivity.

Photochemical Asymmetric Nickel-Catalyzed Acyl Cross-Coupling

Photochemical enantioselective nickel-catalyzed cross-coupling reactions are difficult to implement. We report a visible-light-mediated strategy that successfully couples symmetrical anhydrides and 4-alkyl dihydropyridines (DHPs) to afford enantioenriched α-substituted ketones under mild conditions. The chemistry does not require exogenous photocatalysts. It is triggered by the direct excitation of DHPs, which act as a radical source and as a reductant, facilitating the turnover of the chiral catalytic nickel complex.

Regio- and Enantioselective Iridium-Catalyzed N-Allylation of Indoles and Related Azoles with Racemic Branched Alkyl-Substituted Allylic Acetates

Cyclometallated π-allyliridium C,O-benzoates modified with (S)-tol-BINAP, which are stable to air, water, and SiO₂ , catalyze highly enantioselective N-allylations of indoles and related azoles. This reaction complements previously reported metal-catalyzed indole allylations in that complete levels of N versus C3 and branched versus linear regioselectivity are observed.

Copper-Catalyzed Oxidative C-H Bond Functionalization of N-Allylbenzamide for Regioselective C-N and C-O Bond Formation

Copper-catalyzed oxidative couplings of N-allylbenzamides for C-N and C-O bond formations have been developed through C-H bond functionalization. To demonstrate the utility of this approach, it was applied to the synthesis of β-aminoimides and imides. To the best of our knowledge, these are the first examples in which different classes of N-containing compounds have been directly prepared from the readily available N-allylbenzamides using an inexpensive catalyst/oxidant/base (CuSO₄ /TBHP/Cs₂ CO₃ ) system.

Catalytic Asymmetric N-Alkylation of Indoles and Carbazoles through 1,6-Conjugate Addition of Aza-para-quinone Methides

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.

Enantioselective direct functionalization of indoles by Pd/sulfoxide-phosphine-catalyzed N-allylic alkylation

A general and efficient Pd/sulfoxide-phosphine complex-catalyzed direct asymmetric N-allylic alkylation of indoles has been developed to allow for the preparation of various N-allylated indoles in generally good yields with excellent enantioselectivities. This catalytic system could also be extended to other N-containing heterocycles with good results.