Photomediated Spirocyclization of N-Benzyl Propiolamide with N-Iodosuccinimide for Access to Azaspiro[4.5]deca-6,9-diene-3,8-dione

A metal- and oxidant-free route for affording azaspiro[4.5]deca-6,9-diene-3,8-dione via photomediated iodinated spirocyclization of N-(4-methoxybenzyl) propiolamide has been developed. The reaction underwent a radical addition/ipso-cyclization/dearomatization process at room temperature and successfully constructed C-C and C-I bonds. This green and convenient approach could be generally expanded to produce a range of iodinated spirocyclization products in moderate to good yields.

Radical-mediated rearrangements: past, present, and future

Rearrangement reactions, one of the most significant transformations in organic chemistry, play an irreplaceable role in improving synthetic efficiency and molecular complexity. Concomitant cleavage and reconstruction of chemical bonds can display the great artistry and the glamour of synthetic chemistry. Over the past century, ionic rearrangement reactions, in particular those involving cationic pathways, have represented most of the research. Alongside the renaissance of radical chemistry, radical-mediated rearrangements have recently seen a rapid increase of attention from the chemical community. Many new radical rearrangements that extensively reveal the migratory behaviour of functional groups have been unveiled in the last decade. This Review provides a comprehensive perspective on the area from the past to present achievements, and brings up the prospects that may inspire colleagues to develop more useful synthetic tools based on radical rearrangements.

A computational study for the reaction mechanism of metal-free cyanomethylation of aryl alkynoates with acetonitrile

A computational study of metal-free cyanomethylation and cyclization of aryl alkynoates with acetonitrile is carried out employing density functional theory and high-level coupled-cluster methods, such as coupled-cluster singles and doubles with perturbative triples [CCSD(T)]. Our results indicate that the reaction of aryl alkynoates with acetonitrile in the presence of tert-butyl peroxybenzoate (TBPB) under metal-free conditions tends to proceed through cyanomethylation, spirocyclization and ester migration of the kinetically favoured coumarin derivatives. 1,2-Ester migration in the spiro-radical intermediate 10 does not proceed via the formation of the carboxyl radical 11 suggested by Sun and co-workers. Our results also demonstrate that the t-butoxy radical is substantially responsible the formation of the cyanomethyl radical by the abstraction of a hydrogen atom from acetonitrile.

A computational study of metal-free cyanomethylation and cyclization of aryl alkynoates with acetonitrile is carried out employing density functional theory and high-level coupled-cluster methods, such as [CCSD(T)].

Atom Transfer Oxidative Radical Cascade of Aryl Alkynoates towards 1,1-Dichalcogenide Olefins

An oxidative trifunctionalization of aryl alkynoates has been devised via the chalcogenide radical triggered intramolecular 1,4-aryl migration/decarboxylation cascade to prepare 1,1-dichalcogenide tetrasubstituted alkenes in high yields (up to 98 %). This operationally simple reaction proceeds under metal-free conditions, can be executed on gram scale, and highlights formal 1,1-difunctionalization of alkynes. Synthetic potential of this protocol was demonstrated through a twofold cascade rearrangement to access highly conjugated tetra-selenylated alkenes along with a cross-dehydrogenative annulation to prepare fluorene derivative.

Benzylarylation of N-Allyl Anilines: Synthesis of Benzylated Indolines

An unprecedented benzylic C-H functionalization of methyl arenes across unactivated alkenes is presented. In the presence of MnCl₂·4H₂O and di- tert-butyl peroxide, N-allyl anilines underwent benzylation/cyclization cascade to give benzylated indolines, which are a previously unmet synthetic goal. This protocol features simple operation, broad substrate scope, and great exo selectivity.

Synthesis of tri-substituted allyl alcohols via a copper/iron co-catalyzed cascade perfluoroalkylation/rearrangement of aryl propynyl ethers

A copper/iron co-catalyzed fluoroalkylation of aryl propynyl ethers for the synthesis of perfluoroalkylated tri-substituted allyl alcohol derivatives is reported.

TEMPO promoted direct multi-functionalization of terminal alkynes with 2-oxindoles/benzofuran-2(3H)-one

Highly selective and catalyst-free tandem multi-functionalization of terminal alkynes was developed with 2-oxindoles and benzo-furan-2(3H)-one using TEMPO both as a radical promoter and a trapping reagent. This work expands the scope of the radical-cascade addition/trapping process of alkynes for the effective construction of various β-oxyl carbonyls in moderate to good yields.

A catalyst-free intermolecular trans-iodoalkylation of alkynes

We report the first catalyst-free and trans-selective iodoalkylation reaction of alkynes with a series of α-carbonyl compounds. This unprecedented three-component iodoalkylation reaction is enabled by using (iodoethynyl)trimethylsilane as a radical initiator and iodide source. The 1,2-difunctionalization affords alkenyl iodides, which are versatile building blocks for the construction of tri-substituted alkene derivatives.

Recent advances in radical transformations of internal alkynes

This review highlights the recent progress in the radical transformation of internal alkynes and focuses on the reaction mechanisms by carbon/heteroatom-centered triggered additions, and offers a comprehensive overview on the existing procedures and employed methodologies.

Catalyst-free synthesis of α-thioacrylic acids via cascade thiolation and 1,4-aryl migration of aryl alkynoates at room temperature

A simple and facile catalyst-free strategy has been developed for the synthesis of α-thioacrylic acids from readily-available aryl alkynoates and thiols at room temperature under air.

Tandem trifluoromethylthiolation/aryl migration of aryl alkynoates to trifluoromethylthiolated alkenes

The oxidative trifluoromethylthiolation of aryl alkynoates with AgSCF₃ provided a new access to trifluoromethylthiolated alkenes.

ZnBr2-Mediated oxidative spiro-bromocyclization of propiolamide for the synthesis of 3-bromo-1-azaspiro[4.5]deca-3,6,9-triene-2,8-dione

ZnBr₂-Mediated oxidative ipso-bromocyclization of N-arylpropoilamide was utilized herein for the synthesis of 3-bromo-1-azaspiro[4.5]deca-3,6,9-triene-2,8-dione with high efficiency and a broad tolerance for functional groups.

Fe-Catalyzed oxidative spirocyclization of N-arylpropiolamides with silanes and TBHP involving the formation of C–Si bonds

A new iron-catalyzed oxidative spirocyclization of N-arylpropiolamides with silanes and TBHP leading to 3-silyl spiro[4,5]trienones is presented, which offers a practical route to introduction of silicon-centered radicals across the C–C triple bonds.

Visible-light-mediated oxidative demethylation of N6-methyl adenines

A novel solution for the chemical modulation of RNA epigenetics via biologically compatible photo-catalysis under visible light irradiation has been described.

Metal-Free Cascade Oxidative Decarbonylative Alkylation/Arylation of Alkynoates with Alphatic Aldehydes

The oxidative difunctionalization of aryl alkynoates with alphatic aldehydes as a cheap and abundant alkyl radical source was developed, providing a variety of trisubstituted alkenes in moderate to good yields. In this reaction, radical decarbonylative alkylation of C-C triple bond, 1,4-aryl migration, and decarboxylation were involved under metal-free conditions.

Copper-Catalyzed Oxidative ipso-Annulation of Activated Alkynes with Silanes: An Approach to 3-Silyl Azaspiro[4,5]trienones

A novel strategy of silylation and dearomatization of activated alkynes with silanes to synthesize azaspiro[4,5]trienones is developed, which could be facilely achieved through a tandem difunctionalization of alkyne, dearomatization, and oxidation and provided a facile approach to produce useful 3-silyl azaspiro[4,5]trienones in an efficient manner.

Radical Smiles Rearrangement: An Update

Over the decades the Smiles rearrangement and its variants have become essential synthetic tools in modern synthetic organic chemistry. In this mini-review we summarized some very recent results of the radical version of these rearrangements. The selected examples illustrate the synthetic power of this approach, especially if it is incorporated into a domino process, for the preparation of polyfunctionalized complex molecules.

Transition metal-free decarboxylative alkylation reactions

This review summarizes recent advances in the transition metal-free decarboxylative alkylation of carboxylic acids and their derivatives.