Synthesis of 3,3-Spirocyclic 2-Phosphonoindolines via a Dearomative Addition of Phosphonyl Radicals to Indoles

Synthetic Methods for Azaheterocyclic Phosphonates and Their Biological Activity: An Update 2004-2024

The increasing importance of azaheterocyclic phosphonates in the agrochemical, synthetic, and medicinal field has provoked an intense search in the development of synthetic routes for obtaining novel members of this family of compounds. This updated review covers methodologies established since 2004, focusing on the synthesis of azaheterocyclic phosphonates, of which the phosphonate moiety is directly substituted onto to the azaheterocyclic structure. Emphasizing recent advances, this review classifies newly developed synthetic approaches according to the ring size and providing information on biological activities whenever available. Furthermore, this review summarizes information on various methods for the formation of C-P bonds, examining sustainable approaches such as the Michaelis-Arbuzov reaction, the Michaelis-Becker reaction, the Pudovik reaction, the Hirao coupling, and the Kabachnik-Fields reaction. After analyzing the biological activities and applications of azaheterocyclic phosphonates investigated in recent years, a predominant focus on the evaluation of these compounds as anticancer agents is evident. Furthermore, emerging applications underline the versatility and potential of these compounds, highlighting the need for continued research on synthetic methods to expand this interesting family.

Radical Three-Component Nitro Spiro-Cyclization of Unsaturated Sulfonamides/Amides to Access NO2-Featured 4-Azaspiro[4.5]decanes

Free radical three-component nitration/spirocyclization of unsaturated sulfonamides/amides with tert-butyl nitrite was developed for the construction of diverse NO2-revised 4-azaspiro[4.5]decanes. This tandem system featured metal-free participation, simple operation, good selectivity/yields, and a green/low-cost O source. Meanwhile, one nitro-containing complex molecule and a scaled-up operation were performed well to test the synthetic potential of the cascade reaction. Isotopic labeling, radical inhibition experiments, and DFT analysis were carried out to gain insight into the reaction process.

Iodine(III)-Mediated C-C Bond Coupling to Construct Spirocyclic Indolenines of Various Ring Sizes

Herein, we report a novel iodine(III)-mediated intramolecular dearomative spirocyclization of indole derivatives to generate highly strained spirocyclobutyl, spirocyclopentyl, and spirocyclohexyl indolenines in moderate to good yields. A set of structurally novel, densely functionalized spiroindolenines with broad functional group compatibility was efficiently constructed in this way under mild reaction conditions. Moreover, the β-enamine ester as a versatile functional group in the product provides great convenience for the synthesis of bioactive compounds and related natural products.

Nitro-Spirocyclization of Biaryl Ynones with tert-Butyl Nitrite: Access to NO2-Substituted Spiro[5,5]trienones

A metal/peroxide-free involved simple cascade 6-exo-trig spirocyclization of tert-butyl nitrite with biaryl ynones has been finished, which resulted in various NO₂-modified spiro[5,5]trienones with good regioselectivity/yields. A variety of scaled-up experiments, reduction/epoxidation operations, and mechanistic studies were performed to verify the merits and spirocyclization process of this radical system. Finally, the structure of the spirocycles was confirmed by single-crystal X-ray diffraction.

Enantioselective Radical-Type 1,2-Alkoxy-Phosphinoylation to Styrenes Catalyzed by Chiral Vanadyl Complexes

A series of vanadyl complexes bearing 3-t-butyl-5-bromo, 3-aryl-5-bromo, 3,5-dihalo-, and benzo-fused N-salicylidene-tert-leucinates was examined as catalysts for 1,2-alkoxy-phosphinoylation of 4-, 3-, 3,4-, and 3,5-substituted styrene derivatives (including Me/t-Bu, Ph, OR, Cl/Br, OAc, NO₂ , C(O)Me, CO₂ Me, CN, and benzo-fused) with HP(O)Ph₂ in the presence of t-BuOOH (TBHP) in a given alcohol or cosolvent with MeOH. The best scenario involved the use of 5 mol % 3-(2,5-dimethylphenyl)-5-Br (i.e., 3-DMP-5-Br) catalyst at 0 °C in MeOH. The desired catalytic cross coupling reactions proceeded smoothly with enantioselectivities of up to 95 % ee of (R)-configuration as confirmed by X-ray crystallographic analysis of several recrystallized products. The origin of enantiocontrol and homolytic substitution of the benzylic intermediates by vanadyl-bound methoxide and radical type catalytic mechanism were proposed.

Manganese-Mediated Electrochemical Dearomatization of Indoles To Access 2-Azido Spirocyclic Indolines

An efficient and environmentally friendly electrochemical protocol for dearomatization of indoles was developed, delivering a series of azido-containing spirocyclic indolines with good functional group tolerance. This dearomatization process is proposed to result from the oxidation of Mn^II-N₃ species, supported by cyclic voltammetry experiments. Moreover, synthetic transformations can provide an alternative approach to a range of functionalized indolines.

Visible Light-Promoted Selenylative Spirocyclization of Biaryl Ynones toward the Formation of Selenated Spiro[5.5]trienones

A visible-light induced dearomative cascade cyclization of biaryl ynones with diselenides under photocatalyst and external additive-free conditions has been explored, giving a series of selenated spiro[5.5]trienones in moderate to good...

Facile synthesis of α-aminophosphine oxides from diarylphosphine oxides, arynes and formamides

The straightforward synthesis of α-amino phosphine oxides via three-component reactions involving arynes, formamides and diarylphosphine oxides is disclosed. This method employs the aryne to activate formamide, without an external activating reagent, which is operationally simple under mild conditions with high efficiency. Furthermore, mechanistic perception suggests a cascade sequence including formal [2 + 2] cycloaddition of the aryne with a CO bond, and a 1,4-addition of the H-P(O) compounds to the enamine intermediates.

Synthesis of CF3-Containing Spirocyclic Indolines via a Red-Light-Mediated Trifluoromethylation/Dearomatization Cascade

A red-light-mediated ⁿPr-DMQA⁺-catalyzed cascade intramolecular trifluoromethylation and dearomatization of indole derivatives with Umemoto's reagent has been developed. This protocol provides a facile and efficient approach for the construction of functionalized and potentially biologically important CF₃-containing 3,3-spirocyclic indolines with moderate to high yields and excellent diastereoselectivities under mild conditions. The success of multiple gram-scale (1 and 10 g) experiments further highlights the robustness and practicality of this protocol and the merit of the employment of red light. Mechanistic studies support the formation of a crucial CF₃ radical species and a dearomatized benzyl carbocation intermediate.

Dearomatization Reactions of Indoles to Access 3D Indoline Structures

This Account summarizes our involvement in the development of dearomatization reactions of indoles that has for origin a total synthesis problematic. We present the effort from our group to obtain 3D-indolines scaffold from the umpolung of N-acyl indoles via activation with FeCl3 to the oxidative spirocyclizations of N-EWG indoles and via the use of electrochemistry.

1 Introduction

2 Activation of N-Acyl Indoles with FeCl3

2.1 Hydroarylation of N-Acyl Indoles

2.2 Difunctionalization of N-Acyl Indoles

3 Radical-Mediated Dearomatization of Indoles for the Synthesis of Spirocyclic Indolines

4 Electrochemical Dearomatization of Indoles

4.1 Direct Electrochemical Oxidation of Indoles

4.2 Indirect Electrochemical Oxidation of Indoles

5 Conclusion

Mn-catalyzed radical initiated domino transformation of alkynylated cyclohexadienones with TMSN3 and O2 to bicyclic azido alcohols

An efficient Mn-catalyzed cascade azide radical addition/cyclization/oxygen insertion reaction of alkyne-tethered cyclohexadienones with TMSN3 under mild conditions is reported. This domino reaction presents good diastereoselectivity generating bicyclic azido alcohol scaffolds which can be transformed into useful building blocks in organic synthesis for medicinal chemistry.

Direct Synthesis of Sulfonylated Spiro[indole-3,3'-pyrrolidines] by Silver-Mediated Sulfonylation of Acrylamides Coupled with Indole Dearomatization

A dearomative tandem spiro-cyclization reaction of N-[(1H-indol-3-yl)methyl]methacrylamide derivatives with sulfinate sodium in the presence of AgNO₃ and K₂CO₃ is reported, which produced sulfonylated spiro[indole-3,3'-pyrrolidines] in medium to excellent yields. The characteristics of this transformation contain good functional group tolerance and ease of operation.

Electrochemical synthesis of 3a-bromofuranoindolines and 3a-bromopyrroloindolines mediated by MgBr2

We report an efficient and environmentally friendly electrochemical approach to perform the bromo cyclization of tryptophol, tryptamine and tryptophan derivatives.