Experimental and Theoretical Study on the Regioselective Radical Cyclization Reactions of 1-(o-Alkenylaryl)-2-amido-1-ketones for the Construction of Indeno[2,1-d][1,3]oxazin-9-ones

A simple and efficient two-step method for the construction of novel 2,4,9a-trisubstituted-4a,9a-dihydroindeno[2,1-d][1,3]oxazin-9-ones has been developed. The NHC-catalyzed aza-benzoin reaction of o-alkenyl benzaldehydes with N-acylarylimines afforded 1-(o-alkenylaryl)-2-amido-2-aryl-1-ethanones, which underwent regioselective 5-exo-trig radical cyclization to furnish the three-ring-fused heterocyclic products, generally in good yields. The synthetic method displayed good tolerance toward the nature of substituents, substitution pattern, and steric hindrance of o-alkenyl benzaldehydes. Based on this method, the synthesis of unprecedented dihydrobenzo[6,7]indeno[2,1-d][1,3]oxazin-7-ones and dihydropyrido[2',3':3,4]cyclopenta[1,2-d][1,3]oxazin-9-ones has been achieved by employing o-alkenylnaphthaldehyde and o-alkenylnicotinaldehyde as substrates. The regioselectivity between 5-exo-trig and 6-endo-trig radical cyclization reactions of different 1-(o-alkenylaryl)-2-amido-2-aryl-1-ethanones were elucidated with DFT calculations.

Saturated Boronic Acids, Boronates, and Trifluoroborates: An Update on Their Synthetic and Medicinal Chemistry

This review discusses recent advances in the chemistry of saturated boronic acids, boronates, and trifluoroborates. Applications of the title compounds in the design of boron-containing drugs are surveyed, with special emphasis on α-amino boronic derivatives. A general overview of saturated boronic compounds as modern tools to construct C(sp³ )-C and C(sp³ )-heteroatom bonds is given, including recent developments in the Suzuki-Miyaura and Chan-Lam cross-couplings, single-electron-transfer processes including metallo- and organocatalytic photoredox reactions, and transformations of boron "ate" complexes. Finally, an attempt to summarize the current state of the art in the synthesis of saturated boronic acids, boronates, and trifluoroborates is made, with a brief mention of the "classical" methods (transmetallation of organolithium/magnesium reagents with boron species, anti-Markovnikov hydroboration of alkenes, and the modification of alkenyl boron compounds) and a special focus on recent methodologies (boronation of alkyl (pseudo)halides, derivatives of carboxylic acids, alcohols, and primary amines, boronative C-H activation, novel approaches to alkene hydroboration, and 1,2-metallate-type rearrangements).

Construction of congested Csp3-Csp3 bonds by a formal Ni-catalyzed alkylboration

Through the combination of a Ni-catalyzed alkene alkenylboration followed by hydrogenation, the synthesis of congested Csp³–Csp³-bonds can be achieved. Conditions have been identified that allow for the use of both alkenyl-bromides and -triflates. In addition, the hydrogenation creates another opportunity for stereocontrol, thus allowing access to multiple stereoisomers of the product. Finally, the method is demonstrated in the streamlined synthesis of a biologically relevant molecule.

Through the combination of a Ni-catalyzed alkene alkenylboration followed by hydrogenation, the synthesis of congested Csp³–Csp³-bonds can be achieved.

Copper-catalyzed borylative cyclization of γ,δ-unsaturated aromatic oxime esters to (borylmethyl)pyrrolidines

An efficient copper-catalyzed aminoborylation of γ,δ-unsaturated aromatic oxime esters with bis(pinacolato)diboron has been developed. A variety of α-(borylmethyl)pyrrolidine derivatives were constructed in high yields under mild conditions.

C–C and C–X coupling reactions of unactivated alkyl electrophiles using copper catalysis

Copper catalysts enable cross-coupling reactions of unactivated alkyl electrophiles to generate C–C and C–X bonds.

Palladium-catalyzed intermolecular [4 + 2] formal cycloaddition with (Z)-3-iodo allylic nucleophiles and allenamides

A highly chemo- and regioselective [4 + 2] formal cycloaddition of (Z)-3-iodo allylic nucleophiles and allenamides catalyzed by palladium is reported. The methodology proceeds under mild reaction conditions and is tolerant of alkyl and aryl functional groups. The SN2' substitution at the proximal C[double bond, length as m-dash]C bond performed against the Heck or SN2 pathway delivered a variety of 2-amino-dihydropyrans and 2-amino-tetrahydropiperidines in moderate to satisfactory yields. The [4 + 2] formal cycloaddition derivatives are convertible to interesting scaffolds 2,6,7,7a-tetrahydropyrano[2,3-b]pyrrole and 2,6,7,7a-tetrahydro-1H-pyrrolo[2,3-b]pyridine derivatives via ring-closing metathesis (RCM) with Grubbs catalyst II.

New avenues for C-B bond formation via radical intermediates

This perspective gives an overview on recent findings in the emerging area of C-radical borylation using diborons as radical trapping reagents. Aryl, vinyl and alkyl boronic esters can be accessed via such an approach under mild conditions. These processes are complementary to established transition metal catalysed cross coupling reactions. Radical borylations can be conducted in the absence of a transition metal but some processes require transition metals as catalysts. It will be shown that various readily available C-radical precursors can be used to run these borylations. For a better understanding of the chemistry, mechanistic discussions are also presented and an outlook on this topic will be provided at the end of the article.

Hybrid Reaction Systems for the Synthesis of Alkylated Compounds Based upon Cu-Catalyzed Coupling of Radicals and Organometallic Species

A transition metal catalyzed alkylation with an alkyl halide is one of the most difficult reactions to achieve, because of the difficult oxidative addition of an alkyl-halogen bond to a metal, and the tendency of the resulting alkylmetal intermediate to undergo a β-hydride elimination reaction to give an olefin. In this review, we discuss hybrid reaction systems involving Cu catalyzed combination of radicals and organometallic species, which enable facile alkylation reactions to construct C-C and C-heteroatom bonds. This paper highlights recent progress in arylation, alkenylation, alkynylation, cyclization, addition and introduction of heteroatoms via these hybrid reaction systems.

A palladium-catalyzed regiocontrollable hydroarylation reaction of allenamides with B2pin2/H2O

A novel palladium-catalyzed regiocontrollable hydroarylation reaction of allenamides with B₂pin₂/H₂O has been disclosed.

Total Synthesis of (±)-Crinane from 6,6-Dibromobicyclo[3.1.0]hexane Using a 5- exo- trig Radical Cyclization Reaction to Assemble the C3a-Arylated Perhydroindole Substructure

Crinane embodies the tetracyclic framework associated with some of the most common Amaryllidaceae alkaloids. It has now been prepared in 10 steps from 6,6-dibromobicyclo[3.1.0]hexane (2). The initial step involves the thermally induced electrocyclic ring opening of cyclopropane 3 and capture of the resulting π-allyl cation with benzylamine to give an allylic amine that is readily elaborated to the 3°-amine 10. This last compound was engaged in a 5- exo- trig free radical cyclization reaction to give the C3a-arylated perhydroindole 11. Compound 11 was then converted, over two steps, into (±)-crinane, the hydrochloride salt of which has been subjected to single-crystal X-ray analysis.

Palladium-catalyzed heck-type cascade cyclization of (Z)-1-iodo-1,6-dienes with N-tosyl hydrazones

A new way to synthesize tetrahydropyridine derivatives bearing a terminal alkene due to highly regioselective β-H elimination of alkylpalladium species.