Practical Radical Cyclizations with Arylboronic Acids and Trifluoroborates (original) (raw)
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Journal of Organic Chemistry, 2009
Dicyclohexyl-6-iodohexenylborane efficiently undergoes radical cyclization at room temperature using tri-n-butyltin hydride as a hydrogen donor and without the aide of a radical initiator. Efforts to develop environmentally friendly reagents using hypophosphites as substitutes for tin hydrides in this reaction provided a 60% yield of cyclopentanemethanol when tetrabutylammonium hypophosphite was used. Air was necessary as an initiator when hypophosphites were used. During investigations of the radical cyclization reactions, it was discovered that excess tetrabutylammonium hydroxide provided the rearrangement-cyclization product in excellent yield. Since this product was chiral, efforts were focused on achieving enantioselectivity. Oxazaborolidines made from chiral amino alcohols and 6-tosyl-1hexenylboronic acid were treated with methyllithium to give 1-cyclopentylethanol after oxidation in 60% ee, demonstrating that oxazaborolidines were effective chiral directors for this reaction.
Die Anwendungen von fluorinierten Arylboronaten in der organischen Synthese
2020
Fluorinated compounds are an important motif, particularly in pharmaceuticals, as one-third of the top performing drugs have fluorine in their structures. Fluorinated biaryls also have numerous applications in areas such as material science, agriculture, crystal engineering, supramolecular chemistry, etc. Thus, the development of new synthetic routes to fluorinated chemical compounds is an important area of current research. One promising method is the borylation of suitable precursors to generate fluorinated aryl boronates as versatile building blocks for organic synthesis. Chapter 1 In this chapter, the latest developments in the synthesis, stability issues, and applications of fluorinated aryl boronates in organic synthesis are reviewed. The catalytic synthesis of fluorinated aryl boronates using different methods, such as C–H, C–F, and C–X (X = Cl, Br, I, OTf) borylations are discussed. Further studies covering instability issues of the fluorinated boronate derivatives, which ar...
Organic Letters, 2011
Potassium Boc-protected aminomethyltrifluoroborate, a primary aminomethyl equivalent, was synthesized successfully through a "one-pot" process. With this trifluoroborate, Suzuki-Miyaura cross-coupling reactions were investigated with a variety of both aryl-and hetaryl chlorides in good to excellent yields. Aminomethyl moieties, especially aminomethylated arenes, might be considered privileged substructures because they appear in many bioactive natural products, 1 and they are also used as important intermediates in synthetic organic chemistry (Figure 1). 2 Aminomethylarenes are often synthesized by either reduction of aryl cyanides 3 or oximes 4 (Scheme 1, path A). However, access to primary aminomethyl aryl-and hetaryl compounds with reducible functional groups would not be compatible with this method. An alternative way to install the aminomethylarene moiety is the Staudinger reaction 5 of organic azides with trivalent phosphorus compounds (Scheme 1, path B). Unfortunately, some aryl-and hetaryl azides exhibit significant thermal-or shock-sensitivity. 6 Moreover, the benzylic or pseudobenzylic halide precursors required to prepare the azides are often not readily available.
2013
Chapter 1 briefly covers the development and utility of allylboron reagents in organic synthesis. Transition models proposed for addition to carbonyl groups and imines are discussed and selected examples of the utility of these reagents to the synthesis of complex molecule covered. In chapter 2 the allylation and crotylation of ketones using allyl-and crotyltrifluoroborates and montmorillonite K-10 are described. The method is scalable and utilizes a reliable catalyst with high functional group tolerance. A conventional work-up is not required for further purification, I would like to thank my supervisor Prof. Batey for his exceptional patience, guidance and advice throughout my studies at U of T. You have been a great mentor. I would like to acknowledge Professors Lautens, Dong and Yudin as my thesis committee members for their advice during the committee meetings and informal discussions. I would like to thank my external examiner Prof. Ward for taking time to read my thesis. I am grateful to my former supervisors and indomitable scientists, from whom I have learned life lessons; Prof. Firouzabadi and Prof. Sneickus. My sincerest thanks to John Janetzko, my enthusiastic undergraduate student who collaborated with me on one project and I also cordially thank him and Jordan Goodreid for proof reading my thesis. I have been blessed to work with a cheerful group of people in Batey's lab who have created a fabulous environment for research and fun. Special thanks to current students; Petar Duspara,
ChemInform, 1999
ring closure reactions ring closure reactions O 0130 31-059 Tandem Cyclization of Amidyl Radicals Derived from O-Acyl Hydroxamic Acid Derivatives.-An approach to biologically active bicyclic and tricyclic nitrogen heterocycles is investigated. Tributylstannane/AIBNmediated homolysis of O-acyl hydroxamic acid derivatives (I) and (V) gives amidyl radicals which undergo tandem cyclization, monocyclization, and direct reduction reactions. A similar behavior is observed when Cu(O-Tf) 2 /DBN is employed.-(CLARK,
Radical Fluoroalkylation Reactions
ACS Catalysis
Recent protocols and reactions for catalytic radical perfluoroalkylations (R F = C n F 2n+1 , n ≥ 2) will be described. The production of R F radicals that effect both addition and substitution reactions on organic substrates can be realized through a range of diverse methods such as the well-established visible light transition metal-mediated photocatalysis, organic dye-photocatalyzed reactions, by Electron Donor Acceptor (EDA) complexes or more recently through Frustrated Lewis Pairs (FLP). Thus, perfluoroalkylation reactions of carboncarbon multiple bonds, isocyanides, nitrones, hydrazones, β-ketoesters, αcyano arylacetates, sulfides, and (hetero)arenes will be described. Specially emphasis will be made on examples published after 2015 where higher fluorinated series of fluoroalkylating reagents are studied.
Org. Biomol. Chem., 2009
General details of equipment and techniques used are the same as those we have reported previously. 1 All reactions were carried out under an argon atmosphere, glassware was either flame dried or dried in the oven prior to use. All reactions were set up outside of a glovebox, including the weighing of solid substrates. Pd(PPh) 3 Cl 2 was supplied from Vertellus Specialties UK Ltd or prepared in house, 2 Pd(OAc) 2 was purchased from Aldrich, Pd 2 (dba) 3 was purchased from Alfa Aesar. t-Bu 3 P and D-t-BPF were purchased from Strem, PCy 3 was purchased from Molekula. All other reagents employed were of standard reagent grade, purchased from either Aldrich or Alfa Aesar and used without further purification. Anhydrous solvents were dried through a HPLC column on an Innovative Technology Inc. solvent purification system. All other solvents in this work were used without prior purification. Column chromatography was carried out using 40-60 µm mesh silica (Fluorochem). Thin-layer chromatography (TLC) was performed on 20 mm precoated plates of silica gel (Merck, silica gel 60F 254), visualisation was made using ultraviolet light (254 nm). NMR spectra were recorded on Bruker Avance-400 [ 1 H NMR (400 MHz), 13 C NMR (100 MHz), 11 B NMR (128 MHz)], Varian 500 [ 13 C NMR (125 MHz)], Varian VNMRS 700 [ 13 C NMR (175 MHz)] or Varian 200 [ 19 F NMR (188 MHz)] instruments, using deuterated solvent as a lock. Chemical shifts are quoted in ppm, relative to tetramethylsilane (TMS), using TMS or the residual solvent as internal reference for 1 H and 13 C NMR, and CFCl 3 as internal reference for 19 F NMR. Melting points were determined on a Stuart Scientific SMP3 melting point apparatus and are uncorrected. Electron Impact (EI) mass spectra were recorded on a Thermo-Finnigan Trace with positive ionisation mode. Electrospray (ES +) mass spectra were recorded on a Micromass LCT mass spectrometer. Elemental analyses were obtained on an Exeter analytical Inc. CE-440 elemental analyser. Supplementary Material (ESI) for Organic & Biomolecular Chemistry This journal is (c) The Royal Society of Chemistry 2009 S3 6-(Trifluoromethyl)-3-pyridylboronic acid (3) n-Butyllithium (2.5 M in hexane, 19.5 cm 3 , 49 mmol) was added to a mixture of 5-bromo-2-(trifluoromethyl)pyridine 1 (10.0 g, 44 mmol) and triisopropylborate (12.3 cm 3 , 53 mmol) in anhydrous THF (80 cm 3) at-78 °C under argon. The reaction was stirred at-78 °C for 3 h before warming gradually to-10 °C when the reaction was quenched with deionised water (100 cm 3). The organic solvent was removed in vacuo. The resulting aqueous phase was treated with solid NaOH to obtain pH 10, then washed with diethyl ether (50 cm 3) and acidified to pH 5 using acetic acid. The solution was extracted with EtOAc (200 cm 3) and evaporated to dryness in vacuo to yield 3 as a white solid (8.04 g, 95%): mp