The intramolecular addition of both an alkoxy and acyl substituent across an alkene, oxyacylation of alkenes, using rhodium catalyzed C–O bond activation of an 8-quinolinyl ester is described. Our unsuccessful attempts at intramolecular carboacylation of ketones via C–C bond activation ultimately informed our choice to pursue and develop the intramolecular oxyacylation of alkenes via quinoline-directed C–O bond activation. We provide a full account of our catalyst discovery, substrate scope, and mechanistic experiments for quinoline-directed alkene oxyacylation.

We studied key aspects of the mechanism of Pd-catalyzed C–CN bond activation and intramolecular enantioselective alkene cyanoamidation. An Abboud–Abraham–Kamlet–Taft (AAKT) linear solvation energy relationship (LSER) model for enantioselectivity was established. We investigated the impact of Lewis acid (BPh3), Lewis base (DMPU), and no additives. BPh3 additive led to diminished enantioselectivity and differing results in 13CN crossover experiments, initial rate kinetics, and natural abundance 12C/13C kinetic isotope effect measurements. We propose two catalytic mechanisms to account for our experimental results. We propose that the DMPU/nonadditive pathway passes through a κ2-phosphoramidite-stabilized Pd+ intermediate, resulting in high enantioselectivity. BPh3 prevents the dissociation of CN–, leading to a less rigid κ2-phosphoramidite-neutral Pd intermediate.

Through a close examination of the intermolecular interactions of rubrene (1a) and select derivatives (1b–1p), a clearer understanding of why certain fluorinated rubrene derivatives pack with planar tetracene backbones has been achieved. In this study we synthesized, crystallized, and determined the packing structure of new rubrene derivatives (1h–p). Previously, we proposed that introducing electron-withdrawing CF3 substituents induced planarity by reducing intramolecular repulsion between the peripheral aryl groups (1e–g). However, we found that in most cases, further increasing the fluorine content of rubrene lead to twisted tetracene backbones in the solid state. To understand how rubrene (1a) and its derivatives (1b–p) pack in the solid state, we (re)examined the crystal structures through a systematic study of the close contacts. We found that planar tetracene cores occur when close contacts organize to produce an S symmetry element about a given rubrene molecule. We report the first instance of rubrene derivatives (1l and 1n) that pack in a two-dimensional brick motif. The prospects for new rubrene derivatives in semiconductors were estimated by calculating the reorganization energies of the monomers and transfer integrals of the dimers we observed. Our work allows for the rational design and improved crystal engineering of new rubrene derivatives.

A synthesis of perfluorinated rubrene is reported. Electrochemical analysis revealed the significantly increased electron affinity of perfluororubrene compared with non-modified rubrene. Crystallographic investigation revealed two polymorphs and a solvate, each displaying twisted backbone conformations of perfluororubrene. Taken together, these results suggest perfluororubrene will find applications as a new n-type semiconductor.

The cyclization of an alkene-bearing cyclopentanone to a [2.2.1]-norcamphor ring system is described. The reaction is catalyzed by a combination of rhodium and Brønsted acid. Control experiments indicate that both are needed for acceptable yield. Control experiments with bulky base additives show that rhodium promotes alkene isomerization, likely the first step of this cascade reaction, and that rhodium alone does not promote cyclization. Cyclization is promoted by Brønsted acid in a Prins-type cyclization and carbocation rearrangement process. Trace Brønsted acid present in commercial samples of Rh(cod)2OTf is likely responsible for the observed reaction. Indeed, the norcamphor product can be obtained simply with strong acid, presumably initiated by acid-promoted alkene isomerization. Since our initial motivation for this work was the development of rhodium catalysts for the activation of C–C bonds adjacent to ketones, this communication serves to identify other, perhaps less obvious, pathways for the reactions of unsaturated ketone compounds by the action of rhodium catalysts.

Reported here is a palladium catalyzed intramolecular acylcyanation of alkenes using α-iminonitriles. Through this method, highly functionalized indanones are synthesized in moderate to high yields using Pd(PPh3)4, without need for any additional ligands, and a common Lewis acid (ZnCl2). Additionally, the reaction tolerates substitution at various positions on the aromatic ring including electron donating and electron withdrawing groups.

Alkene oxyacylation is a new strategy for the preparation of β-oxygenated ketones. Now, with Ir catalysis and low-cost salicylate esters, alkene oxyacylation can be promoted by simple and versatile hydroxyl directing groups. This paper discusses catalyst optimization, substituent effects, mechanistic experiments, and the challenges associated with asymmetric catalysis. Crossover experiments point to several key steps of the mechanism being reversible, including the most likely enantiodetermining steps. The oxyacylation products are also prone to racemization without catalyst when heated alone; however, crossover is not observed without catalyst. These observations account for the low levels of enantioinduction in alkene oxyacylation. The versatility of the hydroxyl directing group is highlighted by demonstrating further transformations of the products.

Correlations among the molecular structure, crystal structure, electronic structure, and charge-carrier transport phenomena have been derived from six congeners (2–7) of rubrene (1). The congeners were synthesized via a three-step route from known 6,11-dichloro-5,12-tetracenedione. After crystallization, their packing structures were solved using single-crystal X-ray diffraction. Rubrenes 5–7 maintain the orthorhombic features of the parent rubrene (1) in their solid-state packing structures. Control of the packing structure in 5–7 provided the first series of systematically manipulated rubrenes that preserve the π-stacking motif of 1. Density functional theory calculations were performed at the B3LYP/6-31G(d,p) level of theory to evaluate the geometric and electronic structure of each derivative and reveal that key properties of rubrene (1) have been maintained. Intermolecular electronic couplings (transfer integrals) were calculated for each derivative to determine the propensity for charge-carrier transport. For rubrenes 5–7, evaluations of the transfer integrals and periodic electronic structures suggest these derivatives should exhibit transport characteristics equivalent to, or in some cases improved on, those of the parent rubrene (1), as well as the potential for ambipolar behavior. Single-crystal field-effect transistors were fabricated for 5–7, and these derivatives show ambipolar transport as predicted. Although device architecture has yet to be fully optimized, maximum hole (electron) mobilities of 1.54 (0.28) cm2 V–1 s–1 were measured for rubrene 5. This work lays a foundation to improve our understanding of charge-carrier transport phenomena in organic single-crystal semiconductors through the correlation of designed molecular and crystallographic changes to electronic and transport properties.Keywords: ambipolar transport; crystal engineering; electronic band structure; rubrene derivatives; single-crystal field-effect transistors;

Prior examples of hydroacylation to form six- and seven-membered ring ketones require either embedded chelating groups or other substrate design strategies to circumvent competitive aldehyde decarbonylation. A cooperative catalysis strategy enabled intramolecular hydroacylation of disubstituted alkenes to form seven- and six-membered rings without requiring substrate-embedded chelating groups.

Conditions for the C−CN activation and intramolecular cyanoesterification of alkynes to provide butenolides in good to excellent yields are presented. Pd catalysts, high temperatures/short reaction times (microwave irradiation), and Lewis basic solvents minimized competitive decarbonylation. Less sterically encumbered, electron-rich alkynes underwent cyanoesterification with greater ease compared to sterically encumbered, electron-deficient alkynes. The results led to the hypothesis that migratory insertion of the alkyne, rather than C−CN activation, might be the product-determining step.

The first asymmetric cyanoamidation with synthetically useful enantioselectivity (ee up to 99%) to produce 3,3-disubstituted oxindoles is reported. Palladium catalysts with chiral phosphoramidite ligands activate the cyanoformamide C−CN bond, which is subsequently functionalized with a tethered alkene to give all-carbon quaternary stereocenters. The use of the N,N-(i-Pr)2 derivative of octahydro-MonoPhos allowed the production of oxindoles with high enantioselectivities. Cyanoformamides bearing free N−H groups are now tolerated, potentially allowing protecting-group-free synthesis. Oxindole products of cyanoamidation are rapidly transformed into (+)-horsfiline, (−)-coerulescine, and (−)-esermethole.

Tetrachlorotetracene is an organic semiconductor and has possible applications in flexible organic devices. We have synthesized tetrachlorotetracene in multigram quantities in three steps from commercially available substances, with an overall yield of 52%. X-ray crystallographic analysis of tetrachlorotetracene and its precursor dihydroxytetracenedione showed similar packing structures, with better pitch stacking and roll stacking angles observed for tetrachlorotetracene. Single crystals of tetrachlorotetracene are semiconducting with field effect hole mobility values up to 0.2 cm2/V s. The hole mobility has been measured in the temperature range of 230−290 K, and Arrhenius behavior was observed, with an activation energy of nearly 200 meV. Such a large activation energy suggests significant carrier trapping. Air stability studies showed slow degradation of the crystal surface by atomic force microscopy, along with degradation of the semiconducting properties. We hypothesize that the instability of tetrachlorotetracene to air is the result of decomposition to a quinone species, a degradation previously observed in solution phase studies.

A direct synthesis of new donor materials for organic photovoltaic cells is reported. Diaryindenotetracenes were synthesized utilizing a Kumada–Tamao–Corriu cross-coupling of peri-substituted tetrachlorotetracene with spontaneous indene annulation via C–H activation. Vacuum deposited planar heterojunction organic photovoltaic cells incorporating these molecules as electron donors exhibit power conversion efficiencies exceeding 1.5% with open-circuit voltages ranging from 0.7 to 1.1 V when coupled with C60 as an electron acceptor.

A synthesis of perfluorinated rubrene is reported. Electrochemical analysis revealed the significantly increased electron affinity of perfluororubrene compared with non-modified rubrene. Crystallographic investigation revealed two polymorphs and a solvate, each displaying twisted backbone conformations of perfluororubrene. Taken together, these results suggest perfluororubrene will find applications as a new n-type semiconductor.

Reported here is a palladium catalyzed intramolecular acylcyanation of alkenes using α-iminonitriles. Through this method, highly functionalized indanones are synthesized in moderate to high yields using Pd(PPh3)4, without need for any additional ligands, and a common Lewis acid (ZnCl2). Additionally, the reaction tolerates substitution at various positions on the aromatic ring including electron donating and electron withdrawing groups.