35 research outputs found
Chiral Cyclopentadienyl Ruthenium (II) Complexes:Synthesis and Applications in Catalysis
Cyclopentadienyl ruthenium(II) complexes are an important class of homogenous catalysts. They engage in a multitude of different transformations, for example cycloisomerizations. Due to a lack of suitable chiral cyclopentadienyl ligands, no efficient enantioselective version of the cationic CpRu(MeCN)3PF6 catalyst had been developed in the past, despite synthetic needs and potential. This thesis describes a general synthesis of efficient chiral CpxRu(II) catalysts. An atropchiral C2-symmetric biaryl ligand scaffold proved to be the most suitable and allows for fine-tuning of the corresponding complexes. The synthesis of the best performing ligand has been reduced to six steps form (R)-BINOL by implementing a CâH activation strategy. The cationic catalyst I enabled the highly enantioselective cyclization of yne-enone II to 4H-pyrans III. A tremendous counterion effect on the reaction outcome was observed. In situ formation of neutral CpxRu(II) species IV gave rise to a complementary set of catalysts, competent for an enantioselective formal [2+2] reaction of strained alkenes V and internal alkynes VI. Cyclobutenes VII were rapidly formed under mild conditions. Both propiolates and alkynyltriazenes were suitable substrates, enabling rich follow-up chemistry via derivatization of the product
Chiral Cationic (CpRu)-Ru-x(II) Complexes for Enantioselective Yne-Enone Cyclizations
The cydopentadienyl (Cp) group is a ligand of great importance for many transition-metal complexes used in catalysis. Cationic CpRuII complexes with three free coordination sites are highly versatile catalysts for many atom-economic transformations. We report the synthesis of a family of (CpRuII)-Ru-x complexes with chiral Cp ligands keeping the maximum number of available coordination sites. The cationic members are efficient and selective catalysts for yne-enone cyclizations via formal hetero-Diels-Alder reactions. The transformation proceeds in <1 h at -20 degrees C and provides pyrans in up to 99:1 er. Unsaturated ester or Weinrebamide substrates directly yield the iridoid skeleton
Chiral Cyclopentadienyl Ruthenium Complexes as Versatile Catalysts for Enantioselective Transformations
Ruthenium complexes, in particular cyclopentadienyl ruthenium (II) derivatives, catalyze a vast number of transformations in the field of homogenous catalysis. Herein we describe the first synthesis of efficient chiral cationic cyclopentadienyl ruthenium (II) catalysts and their application in enantioselective cycloisomerizations yielding 4H-pyrans. A tremendous counterion effect on the selectivity was observed and subsequently explored, giving rise to a complementary set of neutral cyclopentadienyl ruthenium (II) complexes able to catalyze asymmetric cyclobutene formations
Chiral Cationic Cp<sup>x</sup>Ru(II) Complexes for Enantioselective Yne-Enone Cyclizations
The
cyclopentadienyl (Cp) group is a ligand of great importance
for many transition-metal complexes used in catalysis. Cationic CpRu<sup>II</sup> complexes with three free coordination sites are highly
versatile catalysts for many atom-economic transformations. We report
the synthesis of a family of Cp<sup>x</sup>Ru<sup>II</sup> complexes
with chiral Cp ligands keeping the maximum number of available coordination
sites. The cationic members are efficient and selective catalysts
for yne-enone cyclizations via formal hetero-Diels–Alder reactions.
The transformation proceeds in <1 h at −20 °C and provides
pyrans in up to 99:1 er. Unsaturated ester or Weinreb-amide substrates
directly yield the iridoid skeleton
Asymmetric Catalysis Powered by Chiral Cyclopentadienyl Ligands
Application of chiral derivatives of the versatile and ubiquitous cyclopentadienyl ligand has long remained an underdeveloped area in asymmetric catalysis. In this Perspective we highlight recent exciting results that demonstrate their enormous potential. In particular, we provide a comparative analysis of the available ligand families, an overview of their complexation chemistry, and an examination of their application in catalytic enantioselective reactions. We also discuss current limitations and speculate on the developments that are necessary to advance the field further
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Livestock Grazing On The National Forests—Why continue to do it?
The Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform March 202
Long-Term Outcomes of Neoadjuvant Intra-arterial Cytoreductive Chemotherapy for Lacrimal Gland Adenoid Cystic Carcinoma
To compare the long-term outcomes after intra-arterial cytoreductive chemotherapy (IACC) with conventional treatment for lacrimal gland adenoid cystic carcinoma (ACC).
Retrospective case series.
Nineteen consecutive patients treated with IACC, followed by orbital exenteration, chemoradiotherapy, and intravenous chemotherapy.
Analyses of the histologic characteristics of biopsy specimens, extent of disease at the time of diagnosis, diagnostic surgical procedures, incidence of locoregional recurrences or distant metastases, disease-free survival time, response to IACC, tumor margins at definitive surgery, and toxicity and complications.
Disease relapse, disease-free survival, and chemotherapeutic complications.
Eight patients with an intact lacrimal artery had significantly better outcomes for survival (100% vs. 28.6% at 10 years), cause-specific mortality, and recurrences (all P = 0.002, log-rank test) than conventionally treated patients from the University of Miami Miller School of Medicine. These 8 patients (group 1) had cumulative 10-year disease-free survival of 100% compared with 50% for 11 patients (group 2) who had an absence of the lacrimal artery or deviated from the treatment protocol (P = 0.035) and 14.3% for conventionally treated patients (P<0.001). Likewise, group 2 was associated with lower cause-specific mortality than the institutional comparator group (P = 0.038). Prior tumor resection with lateral wall osteotomy, delay in IACC implementation or exenteration, and failure to adhere to protocol are risk factors for suboptimal outcomes.
Neoadjuvant IACC seems to improve overall survival and decrease disease recurrence. An intact lacrimal artery, no disruption of bone barrier or tumor manipulation other than incisional biopsy, and protocol compliance are factors responsible for favorable outcomes. The chemotoxicity complication rate is limited and manageable.
The author(s) have no proprietary or commercial interest in any materials discussed in this article
Lateral Canthal Tendon Disinsertion: Clinical Characteristics and Anatomical Correlates
To highlight features of lateral canthal tendon disinsertion (LCTD), provide an algorithm for systematic assessment, and describe the anatomic genesis of signs and symptoms.
Retrospective case series of consecutive patients with lateral canthal tendon disinsertion, who underwent lateral canthal tendon fixation by a single surgeon (DTT) between 2004 and 2011.
One hundred and seventeen eyes in 90 patients underwent lateral canthal tendon fixation. Average age was 69.3 ± 17.9 years. Twenty-three percentage of eyes had undergone lower eyelid blepharoplasty and 52% had undergone lateral canthal tightening; 35% had no previous periocular surgery. Patients with purely involutional lateral canthal tendon disinsertion were significantly older (76.1 ± 7.8 years of age; p < 0.03). Six key features associated with lateral canthal tendon disinsertion were identified. On static evaluation: 1) a blunted or vertically displaced lateral canthal angle; 2) a narrow horizontal fissure with reduced temporal scleral triangle; and 3) pseudo eyelid retraction. On dynamic evaluation with attempted closure: 4) medial and inferior movement of the lateral commissure; 5) incomplete apposition of the eyelid margins in the absence of anterior lamellar shortage; and 6) temporal eyelid imbrication. Improved blink dynamics with manual lateral canthal tendon complex repositioning ("the thumb test") predicted a favorable outcome with surgical tightening in 95.7% of cases.
Lateral canthal tendon disinsertion results in altered eyelid fissure symmetry, blink dynamics, and lacrimal pump function. The authors recommend the mnemonic-A.B.C.: for Aperture configuration, Blink dynamics, and eyelid Closure-to structure the examination of all symptomatic patients. Manual restoration of the disinserted lateral canthal tendon with the "thumb test" predicts favorable outcomes with surgical fixation
The Locking Y Lateral Canthopexy With Osseous Integration: Clinical Experience and Surgical Technique
To describe a surgical technique to correct lateral canthal tendon disinsertion with a strabismus surgery-inspired locking capture of the tendon complex and osseous integration via drill holes.
Retrospective interventional case series including all patients with lateral canthal tendon disinsertion who underwent locking Y lateral canthopexy with drill hole reinforcement by 1 surgeon (D.T.T.) between 2006 and 2011. Outcome measures included resolution of presenting ocular symptoms, improved blink dynamics and lid closure, correction of lagophthalmos and exposure keratopathy, and need for further surgery.
A total of 53 lateral canthopexies with osseous integration were performed in 42 patients who fulfilled clinical criteria for lateral canthal tendon disinsertion. The population was biased toward treatment failures; 81% of eyes (43/53) had a history of prior lateral canthal tightening, and of these 30.2% (16/53) had undergone 3 or more procedures. Postoperatively, all eyes demonstrated improved eyelid position and blink mechanics, and 83% (44/53) had subjective resolution of epiphora and ocular irritation. Lagophthalmos was fully corrected in 95% (19/20) of cases, and corneal staining resolved in 88% (14/16). With a mean follow-up period of 24 months, 3.7% of eyes (2/53) required additional lateral canthal tightening.
The locking Y lateral canthopexy is an effective and durable method for repositioning the lateral canthal tendon complex to improve blink dynamics, eyelid closure, and cosmesis. Even in a population heavily biased toward treatment failure, clinical results are excellent and the reoperation rate is low
Enantioselective Total Synthesis and Absolute Configuration of Apiosporic Acid
The first total synthesis of the polyketide apiosporic
acid is
presented. Key steps are a Julia–Kocienski olefination, a Suzuki–Miyaura
cross-coupling, and an intramolecular Diels–Alder reaction.
The absolute configuration of the natural product was determined