Iodine-Mediated Electrophilic Cyclization Research Articles

Synthesis and Antiproliferative Activity of 2,4,6,7-Tetrasubstituted-2H-pyrazolo[4,3-c]pyridines.

A library of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines was prepared from easily accessible 1-phenyl-3-(2-phenylethynyl)-1H-pyrazole-4-carbaldehyde via an iodine-mediated electrophilic cyclization of intermediate 4-(azidomethyl)-1-phenyl-3-(phenylethynyl)-1H-pyrazoles to 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridines followed by Suzuki cross-couplings with various boronic acids and alkylation reactions. The compounds were evaluated for their antiproliferative activity against K562, MV4-11, and MCF-7 cancer cell lines. The most potent compounds displayed low micromolar GI50 values. 4-(2,6-Diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol proved to be the most active, induced poly(ADP-ribose) polymerase 1 (PARP-1) cleavage, activated the initiator enzyme of apoptotic cascade caspase 9, induced a fragmentation of microtubule-associated protein 1-light chain 3 (LC3), and reduced the expression levels of proliferating cell nuclear antigen (PCNA). The obtained results suggest a complex action of 4-(2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol that combines antiproliferative effects with the induction of cell death. Moreover, investigations of the fluorescence properties of the final compounds revealed 7-(4-methoxyphenyl)-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine as the most potent pH indicator that enables both fluorescence intensity-based and ratiometric pH sensing.

Facile synthesis of iodopyridines from N-propargylic β-enaminones via iodine-mediated electrophilic cyclization

A facile, efficient and general synthetic method for iodopyridines is described. When treated with molecular iodine in the presence of sodium bicarbonate, N-propargylic β-enaminones have underwent electrophilic cyclization to afford iodo-substituted pyridines in good to high yields. Iodocyclization has been found to be general for a broad range of N-propargylic β-enaminones and tolerated the presence of aliphatic, aromatic and heteroaromatic groups with electron-withdrawing and electron-donating substituents. The starting N-propargylic β-enaminones have been prepared by conjugate addition of propargylamine to α,β-alkynic ketones, followed by Sonogashira coupling with aryl iodides.

Iodine-mediated electrophilic tandem cyclization of 2-alkynylbenzaldehydes with anthranilic acid leading to 1,2-dihydroisoquinoline-fused benzoxazinones

An efficient iodine-mediated electrophilic tandem cyclization of substituted 2-alkynylbenzaldehydes with anthranilic acids under basic medium leading to iodo-1,2-dihydroisoquinoline-fused benzoxazinones is presented. Success of the protocol for the reaction of substituted 2-alkynylbenzaldehydes with 2-aminobenzamides to furnish isoquinoline-fused quinazolinones is also described.

Key Intermediates of Iodine‐Mediated Electrophilic Cyclization: Isolation and Characterization in an Osmabenzene System

Caught in the act: Key intermediates in an iodine-mediated electrophilic cyclization reaction was isolated by introducing metallabenzenes as the starting material. The unique structure of the intermediate should be described as the intimate ion pair form, instead of the widely accepted iodonium ion form.

Synthesis and cytotoxic activity of 3-phenyl-4-substituted-β-carbolines

Abstract A new class of 3-phenyl-4-substituted- β -carbolines via iodine-mediated electrophilic cyclization as key step were synthesized and their inhibitory activity against three tumor cell lines was evaluated in vitro . It was found that some of the tested compounds showed better cytotoxicity against HeLa and MCF-7 cells than harmine.

ChemInform Abstract: Facile Synthesis of Diiodinated Dihydronaphthalenes and Naphthalenes via Iodine Mediated Electrophilic Cyclization.

AbstractA variety of dihydronaphthalenes is readily prepared by electrophilic iodocyclization of aryl propargyl alcohols.

Synthesis of Isoquinolines by I2-Mediated Electrophilic Heteroannulation

Reported here is the synthesis of highly substituted isoquinolines 2 via the iodine-mediated electrophilic cyclization of 2-alkynyl-1-methylene azido arenes 1. Several sets of conditions were identified using different iodonium sources, depending on the reactivity of the substrate. Both electron-donating and -withdrawing groups are equally tolerated on the aromatic ring, although electron-neutral and -donating groups are clearly favored at the alkyne terminus. The ­reaction was extended to include heterocyclic substrates including pyridines, pyrroles, furans and thiophenes 3, to give the corresponding isoquinolines in poor to excellent yield. The utility of this methodology was further demonstrated by the short synthesis of the potent antitumor agent norchelerythrine. A plausible mechanism involving formation of an iodonium species that is intercepted by the azido group, followed by aromatization on loss of N2 is suggested.

Diversity-Oriented Synthesis of Substituted Furo[2,3-b]pyrazines

A highly efficient method for the synthesis of diversely substituted furo[2,3-b]pyrazines has been elaborated. The Ag+- or iodine-mediated electrophilic cyclization of readily generated 5-chloro-3-substituted ethynyl-1-(4-methoxybenzyl)-pyrazin-2(1H)-ones affords substituted furo[2,3-b]pyrazines, which undergo various palladium catalyzed reactions to generate a library of difficult to attain diversely substituted furo[2,3-b]pyrazines.

Iodine-Mediated Electrophilic Cyclization of 2-Alkynyl-1-methylene Azide Aromatics Leading to Highly Substituted Isoquinolines and Its Application to the Synthesis of Norchelerythrine

The reaction of 2-alkynyl-1-methylene azide aromatics 1 with iodine and/or other iodium donors, such as the Barluenga reagent (Py2IBF4/HBF4) and NIS, gave highly substituted cyclization products, namely, the 1,3-disubstituted 4-iodoisoquinolines 2, in good to high yields. Not only simple 2-alkynyl benzyl azides 1a-j and their substituted analogues 1k-u and 6 but also heteroaromatic analogues, including pyridine 8, pyrroles 10a-c, furane 10d, and thiophenes 10e-g, gave the corresponding isoquinoline derivatives in excellent to allowable yields. Electron-donating and electron-accepting substituents on the aromatic ring were equally tolerated, and either acidic or basic (or even neutral) reaction conditions, depending on the reactivity of the substrate, could be applied to smoothly convert the azide starting materials into the desired isoquinoline products in moderate to good yields. Limits were found only in connection with the substituent at the alkyne terminus, where electron-neutral or electron-donating substituents are clearly favored. The iodine-mediated electrophilic cyclization of 1 most probably proceeds through the iodonium ion intermediate 4 followed by nucleophilic cyclization of the azide and subsequent elimination of N2. This new methodology was successfully applied to the short synthesis of norchelerythrine.

Iodine-mediated electrophilic cyclization of 2-alkynylbenzaldoximes leading to the formation of iodoisoquinoline N-oxides

Reaction of 2-alkynylbenzaldoximes 1 with 5 equiv of iodine in EtOH at room temperature gives the corresponding iodoisoquinoline N-oxides 2 in good to excellent yields. The cyclization proceeds very smoothly and quickly without any additives such as bases under very mild reaction conditions.