Benzotriazole-Triggered Three-Component Lewis Acid-Catalyzed Ring-Opening 1,3-Aminofunctionalization of Donor-Acceptor Cyclopropanes

Lewis Acid-Enabled Chemodivergent Cycloadditions of Donor-Acceptor Cyclopropanes with Indoline-2-Thiones

Lewis acid-enabled reactions of donor-acceptor cyclopropanes (DACs) with indoline-2-thiones are reported. The reaction exhibits tunable annulation depending on the Lewis acid and the substituent at N1 of the indoline-2-thiones. With AlCl3 as the Lewis acid and 1-isopropylindoline-2-thiones as reactants, a direct ring opening with DACs, followed by intramolecular nucleophilic addition/dehydration takes place leading to the formation of dihydro-2H-thiepino[2,3-b]indoles in moderate to good yields. Using Yb(OTf)3 as promoter and 1-unsubstituted indoline-2-thiones as reactants, a (3 + 2) cycloaddition with DACs accompanied by sulfur rearrangement nucleophilic addition/dehydration takes place to give 3-indolyl-4,5-dihydrothiophenes in moderate yields. In addition, the synthetic transformation of 3-indolyl-4,5-dihydrothiophene to sulfone and indole-based axially chiral scaffolds further extends the synthetic utility and structural complexity.

Accessing Azetidines through Magnesium-Mediated Nitrogen Group Transfer from Iminoiodinane to Donor-Acceptor Cyclopropanes

Herein, we report a Lewis acid-mediated ring expansion of donor-acceptor cyclopropanes (DACs) to substituted azetidines via nucleophilic nitrogen group transfer from readily accessible iminoiodinane. This protocol operates under mild, transition-metal-free conditions, and showcases excellent chemoselectivity, along with broad functional group tolerance. We report for the first time that challenging alkyl donor-acceptor cyclopropanes can undergo ring expansion leading to aliphatic azetidines without relying on external oxidants or precious transition-metal catalysts. Mechanistically, the coordination of a magnesium (Mg)-Lewis acid to the DAC promotes nucleophilic ring opening with a putative Mg-amide species generated from the iminoiodinane under the reaction conditions to furnish the azetidine products.

Synthesis of Tetrasubstituted Enamines Using Secondary Amines and In Situ-Generated Allenes from Nitrocyclopropanes

A novel reaction of cyclic and acyclic secondary amines with in situ-generated allene intermediate species from nitro-substituted donor-acceptor cyclopropanes is reported. In the presence of a simple inorganic base, NaOH, tetrasubstituted enamine derivatives can be obtained in moderate to excellent yields. The reaction is operationally easy, features mild reaction conditions and simple inorganic bases, and is free of transition metals.

Sn(OTf)2-Catalyzed (3 + 2) Cycloaddition/Sulfur Rearrangement Reaction of Donor-Acceptor Cyclopropanes with Indoline-2-thiones

The (3 + 2) cycloaddition/sulfur rearrangement reaction of donor-acceptor cyclopropanes bearing a single keto acceptor with indoline-2-thiones has been realized. Under the catalysis of Sn(OTf)2, a series of functionalized 3-indolyl-4,5-dihydrothiophenes were synthesized with moderate to excellent yields.

Lewis acid-catalyzed one-pot thioalkenylation of donor-acceptor cyclopropanes using in situ generated dithiocarbamates and propiolates

Lewis acid-catalyzed one-pot 1,3-thioalkenylation of donor-acceptor (D-A) cyclopropanes has been demonstrated employing in situ generated dithiocarbamates (from amines and CS2) as nucleophilic triggers and alkyl propiolates as electrophiles. This method addresses the limitations of previously known carbothiolation approach, eliminating the need for extra filtration prior to the subsequent trapping with electrophiles. The anticipated thioalkenylated products were obtained in good to excellent yields with a moderate to good E/Z ratio. Three new bonds (C-N, C-S, and C-C) are formed during this 1,3-bisfunctionalization reaction. Notably, employing enantiomerically pure D-A cyclopropanes resulted in enantiopure 1,3-thioalkenylated products, underscoring the stereospecific nature of the developed reaction.

Regioselective C3-H Alkylation of Imidazopyridines with Donor-Acceptor Cyclopropanes

Alkylated imidazopyridines are crucial structures for medicinal chemistry. Here, an efficient method for the C3-H alkylation of imidazopyridines was devised. Under Lewis acid-catalyzed conditions, reactions of imidazopyridines with different donor-acceptor cyclopropanes were carried out. Finally, 1,3-bisfunctionalizaton of donor-acceptor cyclopropanes was performed. In addition, synthesized C3-alkylated imidazopyridines are amenable for diverse synthetic applications.

AlCl3-mediated ring-opening reactions of indoline-2-thiones with acyl cyclopropanes, bi-cyclopropanes and spirocyclic cyclopropanes

AlCl3-mediated nucleophilic ring-opening reactions of indoline-2-thiones with various acyl cyclopropanes, bi-cyclopropanes and spirocyclic cyclopropanes were investigated. A series of ketones functionalized with indolylthio groups were synthesized in yields ranging from moderate to good. Moreover, chemical transformations of 4-indolylthio butan-1-ones to dihydro-2H-thiepino[2,3-b]indoles and sulfone were carried out to further expand both synthetic utility and structural complexity.