Exploring hydroamination-cycloaddition-fragmentation sequences to access polycyclicguanidines and vinyl-2-aminoimidazoles.

The intramolecular hydroamination of a guanidine on an eneyne unit affords a guanidine-substituted diene capable of reacting with dienophiles. These substrates undergo [4+2]-cycloaddition reactions to generate a series of complex cyclic- and spirocyclic-guanidines. Select substrates can further undergo a ring opening-elimination cascade that ultimately reveals a vinyl-2-aminoimidazole. As such this cascade reaction may find application in the synthesis of oroidin-type natural products and their analogues.

Synthesis of Naamidine A and Selective Access to N(2)-Acyl-2-aminoimidazole Analogues.

A short and scalable synthesis of naamidine A, a marine alkaloid with a selective ability to inhibit epidermal growth factor receptor (EGFR)-dependent cellular proliferation, has been achieved. A key achievement in this synthesis was the development of a regioselective hydroamination of a monoprotected propargylguanidine to deliver N(3)-protected cyclic ene-guanidines. This permits the extension of this methodology to prepare N(2)-acyl analogues in a fashion that obviates the troublesome acylation of the free 2-aminoimidazoles, which typically yields mixtures of N(2)- and N(2),N(2)-diacylated products.

Dehydrative C-H alkylation and alkenylation of phenols with alcohols: expedient synthesis for substituted phenols and benzofurans.

A well-defined cationic Ru-H complex catalyzes the dehydrative C-H alkylation reaction of phenols with alcohols to form ortho-substituted phenol products. Benzofuran derivatives are efficiently synthesized from the dehydrative C-H alkenylation and annulation reaction of phenols with 1,2-diols. The catalytic C-H coupling method employs cheaply available phenols and alcohols, exhibits a broad substrate scope, tolerates carbonyl and amine functional groups, and liberates water as the only byproduct.

Design and Testing of Augmented Reality-Based Fluorescence Imaging Goggle for Intraoperative Imaging-Guided Surgery.

The different pathways between the position of a near-infrared camera and the user's eye limit the use of existing near-infrared fluorescence imaging systems for tumor margin assessments. By utilizing an optical system that precisely matches the near-infrared fluorescence image and the optical path of visible light, we developed an augmented reality (AR)-based fluorescence imaging system that provides users with a fluorescence image that matches the real-field, without requiring any additional algorithms. Commercial smart glasses, dichroic beam splitters, mirrors, and custom near-infrared cameras were employed to develop the proposed system, and each mount was designed and utilized. After its performance was assessed in the laboratory, preclinical experiments involving tumor detection and lung lobectomy in mice and rabbits by using indocyanine green (ICG) were conducted. The results showed that the proposed system provided a stable image of fluorescence that matched the actual site. In addition, preclinical experiments confirmed that the proposed system could be used to detect tumors using ICG and evaluate lung lobectomies. The AR-based intraoperative smart goggle system could detect fluorescence images for tumor margin assessments in animal models, without disrupting the surgical workflow in an operating room. Additionally, it was confirmed that, even when the system itself was distorted when worn, the fluorescence image consistently matched the actual site.

Endoscopic sentinel lymph node biopsy using indocyanine green-neomannosyl human serum albumin.

OBJECTIVE: The aim of this study was to determine the possibility of endoscopic sentinel lymph node biopsy of the head and neck region using indocyanine green-neomannosyl human serum albumin (ICG:MSA) and a custom-made intraoperative color-and-fluorescence-merged imaging system (ICFIS). METHODS: Using mouse and rabbit models of tongue cancer, we performed sentinel lymph node biopsy using an ICG:MSA tracer and custom imaging system equipped with an endoscope. RESULTS: ICG:MSA was localized to the cervical lymph node on the ipsilateral side for up to 30 minutes compared to ICG tracer (ICG n = 3, IGC:MSA n = 3). Detection of sentinel lymph nodes was attempted after injecting ICG:MSA in the mouse tongue cancer model (n = 3). During the operation, lymph nodes were easily identified and resected using ICFIS without the aid of other magnifiers. In the rabbit tongue cancer model (n = 3), the ICFIS equipped with 30-degree endoscopy was used to confirm the feasibility of endoscopic sentinel lymph node biopsy. The entire sentinel lymph node biopsy procedure was performed using the ICFIS with the 30-degree endoscope. We detected and dissected sentinel lymph nodes in the rabbit model without the other sentinel lymph node detection tools. CONCLUSION: We confirmed the usefulness of sentinel lymph node biopsy using a near infrared fluorescence technique and endoscopic system. Avoidance of radiation exposure and shine-through phenomena, which are problems of sentinel lymph node biopsy using conventional radioisotopes, are advantages of our surgical technique. By combining the endoscopic system with a sentinel lymph node biopsy procedure, we avoided visible neck scars, which lead to excellent cosmetic outcomes. LEVEL OF EVIDENCE: NA. Laryngoscope, 128:E135-E140, 2018.

Synthesis of bicyclic guanidines via cascade hydroamination/Michael additions of mono-N-acryloylpropargylguanidines.

A cascade silver(I)-catalyzed hydroamination/Michael addition sequence has been developed to deliver highly substituted bicyclic guanidines. This transformation gives rise to geometrically and constitutionally stable ene-guanidines and generates a remote stereocenter with moderate to high diastereoselectivity.

Scope and Mechanistic Study of the Coupling Reaction of α, ß-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways.

The cationic ruthenium-hydride complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to α,ß-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic C-H bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as: rate = k[1](1)[propene](0)[cinnamate](-1). A negligible deuterium kinetic isotope effect (k(H)/k(D) = 1.1±0.1) was measured from both (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) and (E)-C(6)H(5)CD=C(CH(3))CONHCH(3) with styrene. In contrast, a significant normal isotope effect (k(H)/k(D) = 1.7±0.1) was observed from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene and styrene-d(10). A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C(6)H(5)CH=CHCO(2)Et with propene ((13)C(recovered)/(13)C(virgin) at C(ß) = 1.019(6)), while a negligible carbon isotope effect ((13)C(recovered)/(13)C(virgin) at C(ß) = 0.999(4)) was obtained from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene. Hammett plots from the correlation of para-substituted p-X-C(6)H(4)CH=CHCO(2)Et (X = OCH(3), CH(3), H, F, Cl, CO(2)Me, CF(3)) with propene and from the treatment of (E)-C(6)H(5)CH=CHCO(2)Et with a series of para-substituted styrenes p-Y-C(6)H(4)CH=CH(2) (Y = OCH(3), CH(3), H, F, Cl, CF(3)) gave the positive slopes for both cases (ρ = +1.1±0.1 and +1.5±0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, Δ H(‡) = 20±2 kcal mol(-1) and S(‡) = -42±5 e.u. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies.

Selective catalytic C-H alkylation of alkenes with alcohols.

Alkenes and alcohols are among the most abundant and commonly used organic feedstock in industrial processes. We report a selective catalytic alkylation reaction of alkenes with alcohols that forms a carbon-carbon bond between vinyl carbon-hydrogen (C-H) and carbon-hydroxy centers with the concomitant loss of water. The cationic ruthenium complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4)(-) (Cy, cyclohexyl) catalyzes the alkylation in solution within 2 to 8 hours at temperatures ranging from 75° to 110°C and tolerates a broad range of substrate functionality, including amines and carbonyls. Preliminary mechanistic studies are inconsistent with Friedel-Crafts-type electrophilic activation of the alcohols, suggesting instead a vinyl C-H activation pathway with opposite electronic polarization.

Chelate-Assisted Oxidative Coupling Reaction of Arylamides and Unactivated Alkenes: Mechanistic Evidence for Vinyl C-H Bond Activation Promoted by an Electrophilic Ruthenium-Hydride Catalyst.

The cationic ruthenium-hydride complex [(η(6)-C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) was found to be a highly regioselective catalyst for the oxidative C-H coupling reaction of aryl-substituted amides and unactivated alkenes to give ortho-alkenylamide products. The kinetic and spectroscopic analyses support a mechanism involving a rapid vinyl C-H activation followed by a rate-limiting C-C bond formation steps.

Aqueous phase C-H bond oxidation reaction of arylalkanes catalyzed by a water-soluble cationic Ru(III) complex [(pymox-Me2)2RuCl2]+BF4-.

The cationic complex [(pymox-Me(2))RuCl(2)](+)BF(4)(-) was found to be a highly effective catalyst for the C-H bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH(3) at room temperature. Both a large kinetic isotope effect (k(H)/k(D) = 14) and a relatively large Hammett value (rho = -1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species.