Visible-Light-Promoted Tandem Skeletal Rearrangement/Dearomatization of Heteroaryl Enallenes.

Access to complex three-dimensional molecular architectures via dearomatization of ubiquitous aryl rings is a powerful synthetic tool, which faces, however, an inherent challenge to overcome energetic costs due to the loss of aromatic stabilization energy. Photochemical methods that allow one to populate high-energy states can thus be an ideal strategy to accomplish otherwise prohibitive reaction pathways. We present an original dearomative rearrangement of heteroaryl acryloylallenamides that leads to complex fused tricycles. The visible-light-promoted method occurs under mild conditions and tolerates a variety of functional groups. According to DFT modeling used to rationalize the outcome of the cascade, the reaction involves a sequential [2+2] allene-alkene photocycloaddition, which is followed by a selective retro- [2+2] step that paves the way for the dearomatization of the heteroaryl partner. This scenario is original with respect to the reported photochemical reactivity of similar substrates and thus holds promise for ample future developments.

Visible-Light-Driven Decarboxylative Borylation: Rapid Access to α- and ß-Amino-boronamides.

In this study, we described a two-step process involving an efficient visible-light-induced decarboxylative borylation of α- and ß-amino redox-active esters with bis(catecholato)diboron, followed by transamination with 1,8-diaminonapthalene (DANH2). A series of boronamides were obtained in moderate to excellent yields in this one-pot procedure. The photochemical process proved to be very efficient even when conducted under flow conditions with shorter reaction durations and scalable synthesis of DAN boronates.

Base-promoted Conia-ene cyclization of propargyl amides.

We report a tBuOK-promoted synthesis of 1,3-dihydro-2H-pyrrol-2-one and 4-methylenepyrrolidin-2-one systems via Conia-ene like intramolecular cyclization. The method features extremely short reaction times (5 min) and mild reaction conditions (rt), enabling the trapping of a propargyl unit by an amide enolate. An intriguing anionic chain mechanism is at work, which can trigger the isomerization of an exo-alkene giving access to the otherwise elusive endo-product.

Visible-Light Promoted Intramolecular para-Cycloadditions on Simple Aromatics.

Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitization of allenamides. The visible-light-promoted process gives complex [2.2.2]-(hetero)-bicyclooctadienes at room temperature, likely through the stabilization of transient (bi)radicals by naphthalene. The reaction tolerates several valuable functionalities, offering a convenient handle for a myriad of applications, including original isoindoles and metal complexes.

Dimerizing cascades of enallenamides reveal the visible-light-promoted activation of cumulated C-C double bonds.

The visible-light-promoted activation of conjugated C-C double bonds is well developed, while that of cumulated systems is underexplored. We present the feasibility of this challenging approach. The localization of a triplet on an allenamide arm can be favored over that on a conjugated alkene. Allenamides with an arylacryloyl arm dimerize at room temperature in the presence of visible light and an iridium(iii) photocatalyst. Two orthogonal polycyclizations took place and their outcome is entirely dictated by the substitution of the alkene partner. Both cascades afford complex molecular architectures with high selectivity. Products form through the ordered rearrangement of twelve π electrons, providing a [3.2.0] bicyclic unit tethered to a fused tricycle, whose formation included an aryl C-H functionalization step, using disubstituted alkenes. The outcome was reverted with trisubstituted ones, which gave rise to taxane-like bridged tricycles that had two six-membered lactams flanking a cyclooctane ring, which was established through the creation of four alternate C-C bonds.

Inter/Intramolecular Cascade of 1,6-Enynes Catalyzed by All-Metal Aromatic Tripalladium Complexes and Carboxylic Acids.

Trinuclear all-metal aromatic clusters are an original class of molecules with a cyclic and planar metal core. Characterized by peculiar metal-metal delocalized bonds, they represent a new frontier in transition-metal catalysis. We report a study on C-C-forming reactions of polyunsaturated substrates catalyzed by trinuclear all-metal aromatic palladium clusters. The synthesis of two new families of tricyclic compounds was obtained with a broad functional group tolerance under mild reaction conditions. A peculiar regio- and diastereoselectivity characterized the method, demonstrating that trinuclear palladium complexes are complementary to their popular mononuclear peers. Furthermore, preliminary studies on the mechanism of these polycyclization reactions revealed unique features of the homogeneous catalytic system.

Orthogonal Syntheses of 3.2.0 Bicycles from Enallenes Promoted by Visible Light.

Enallenes can be readily converted into two families of 3.2.0 (hetero)bicycles with high diastereoselectivities through the combination of visible light with a suitable Ir(III) complex (1 mol %). Two complementary pathways, namely, a photocycloaddition versus a radical chain, can then take place. Both manifolds grant complete regiocontrol of the allene difunctionalization. This is accompanied by an original 1,3-group shift using sulfonyl allenamides that deliver a congested tetrasubstituted headbridging carbon in the corresponding product.