81826-67-7Relevant articles and documents
Tebbe-like and Phosphonioalkylidene and -alkylidyne Complexes of Scandium
Baik, Mu-Hyun,Carroll, Patrick J.,Gau, Michael R.,Gu, Jun,Lee, Eunji,Mindiola, Daniel J.,Zatsepin, Pavel
, p. 10143 - 10152 (2020)
The bonding between scandium and carbon in a series of alkylidene- and alkylidyne-like moieties is compared. The Tebbe analogue complex (PNP)Sc(μ2-CHSiMe3)(μ2-CH3)[Al(CH3)(CH2SiMe3)] (2) (PNP- = N[2-PiPr2-4-methylphenyl]2) could be formed by adding AlMe3 to (PNP)Sc(CH2SiMe3)2 (1). The fluxional behavior of 2 is studied by a combination of 2D 13C-1H HMQC, HMBC, and other heteronuclear NMR spectroscopic experiments. The phosphonioalkylidene complex (PNP)Sc(CHPPh3)(CH3) (3) could be prepared from 2 by treatment with 2 equiv of the ylide H2CPPh3 or by methane elimination from (PNP)Sc(CH3)2 and 1 equiv of H2CPPh3. The reactivity of the alkylidene in 2 was further explored with N3Ad, which gave insertion at the Sc-C bond, yielding (PNP)Sc(CH3)[η2-N3AdCHSiMe3Al(CH3)(CH2SiMe3)] (4), while DMAP provided C-H activation across the alkylidene with loss of the Al-C bond to form (PNP)Sc(η2-NC5H3NMe2)(CH2SiMe3) (5). Utilizing the same approach that yielded 2, methane elimination in 3 could further be promoted with Al(CH3)3 to furnish the first example of a scandium phosphonioalkylidyne complex, (PNP)Sc(μ2-CPh3)(μ2-CH3)Al(CH3)2 (6). Experimental and theoretical studies were combined to compare the bonding in 2, 3, and 6, in order to understand the legitimacy of Sc-C multiple bond character.
Kinetics of initiation, propagation, and termination for the [rac-(C2H4(1-indenyl)2)ZrMe][MeB(C 6F5)3]-catalyzed polymerization of 1-hexene
Liu,Somsook,White,Rosaaen,Landis
, p. 11193 - 11207 (2001)
Metallocene-catalyzed polymerization of 1-alkenes offers fine control of critical polymer attributes such as molecular weight, polydispersity, tacticity, and comonomer incorporation. Enormous effort has been expended on the synthesis and discovery of new
Sterically crowded cyclohexanes - 9. Synthesis, conformation and dynamics of hexaspiro[2.0.4.0.2.0.4.0.2.0.4.0]tetracosane
Wulf, Karin,Klages, Ulrich,Rissom, Beate,Fitjer, Lutz
, p. 6011 - 6018 (1997)
The synthesis, conformation and dynamics of hexaspiro[2.0.4.0.2.0.4.0.2.0.4.0]tetracosane (3) are described. At room temperature in solution, 3 exists as 4 : 1 mixture of a rapidly interconverting twistboat conformation and a fixed chair conformation. The
Rhodium-Catalyzed Stitching Polymerization of 1,5-Hexadiynes and Related Oligoalkynes
Ikeda, Sho,Shintani, Ryo
, p. 5734 - 5738 (2019)
A new mode of polymerization, rhodium-catalyzed stitching polymerization, has been developed for the synthesis of π-conjugated polymers with bridged repeating units from nonconjugated 1,5-hexadiynes containing both terminal and internal alkyne moieties as monomers. The polymerization proceeded smoothly with a high degree of stitching efficiency under mild conditions, and 1,5,9-decatriyne and 1,5,9,13-tetradecatetrayne monomers could also be employed. The present polymerization strategy would be particularly beneficial for the synthesis of polymers consisting of a repeating unit that is difficult to prepare as a stable monomer because it does not require the use of a preformed bridged π-conjugated monomer.
An α-Cyclopropanation of Carbonyl Derivatives by Oxidative Umpolung
Bauer, Adriano,Di Mauro, Giovanni,Li, Jing,Maulide, Nuno
supporting information, p. 18208 - 18212 (2020/08/21)
The reactivity of iodine(III) reagents towards nucleophiles is often associated with umpolung and cationic mechanisms. Herein, we report a general process converting a range of ketone derivatives into α-cyclopropanated ketones by oxidative umpolung. Mechanistic investigation and careful characterization of side products revealed that the reaction follows an unexpected pathway and suggests the intermediacy of non-classical carbocations.
Hemisynthesis of 2,3,4-13C3-1,4-androstadien-3,17-dione: A key precursor for the synthesis of 13C3-androstanes and 13C3-estranes
Berthonneau, Clément,Nun, Pierrick,Rivière, Matthieu,Pauvert, Mickael,Dénès, Fabrice,Lebreton, Jacques
supporting information, p. 3727 - 3737 (2018/04/14)
In this contribution, we describe two simple and efficient routes for the preparation of keto-aldehyde 1, a key intermediate for the synthesis of 13C3-androstanes and 13C3-estranes. In the first route, the targeted aldehyde 1 was obtained in 40% overall yield from 1,4-androstadien-3,17-dione (3 mmol scale) via a two-step sequence involving a one-pot, abnormal ozonolysis/sulfur oxidation/retro-Michael/ozonolysis process. Alternatively, a second route from 4-androsten-3,17-dione, using a six-step sequence, was optimized to produce 40 mmol batches of the key intermediate 1 in 42% overall yield. At the final stage, the A-ring was reconstructed through a Wittig reaction with the 1-triphenylphosphoranylidene-13C3-2-propanone 2, followed by an intramolecular condensation assisted by thioacetic acid via a Michael addition/retro-Michael reaction sequence to provide 2,3,4-13C3-1,4-androstadien-3,17-dione.
Intramolecular Acetyl Transfer to Olefins by Catalytic C?C Bond Activation of Unstrained Ketones
Rong, Zi-Qiang,Lim, Hee Nam,Dong, Guangbin
supporting information, p. 475 - 479 (2018/02/21)
A rhodium-catalyzed intramolecular acetyl-group transfer has been achieved through a “cut and sew” process. The challenge arises from the existence of different competitive pathways. Preliminary success has been achieved with unstrained enones that contain a biaryl linker. The use of an electron-rich N-heterocycilc carbene (NHC) ligand is effective to inhibit undesired β-hydrogen elimination. Various 9,10-dihydrophenanthrene derivatives can be prepared with excellent functional-group compatibility. The 13C-labelling study suggests that the reaction begins with cleavage of the unstrained C?C bond, followed by migratory insertion and reductive elimination.
Synergistic O3 + OH oxidation pathway to extremely low-volatility dimers revealed in β-pinene secondary organic aerosol
Kenseth, Christopher M.,Huang, Yuanlong,Zhao, Ran,Dalleska, Nathan F.,Caleb Hethcox,Stoltz, Brian M.,Seinfeld, John H.
, p. 8301 - 8306 (2018/09/11)
Dimeric compounds contribute significantly to the formation and growth of atmospheric secondary organic aerosol (SOA) derived from monoterpene oxidation. However, the mechanisms of dimer production, in particular the relevance of gas- vs. particle-phase c
Z -selective alkene isomerization by high-spin cobalt(II) complexes
Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
supporting information, p. 945 - 955 (2014/02/14)
The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
Epoxidation of bromoallenes connects red algae metabolites by an intersecting bromoallene oxide-Favorskii manifold
Christopher Braddock,Clarke, James,Rzepa, Henry S.
supporting information, p. 11176 - 11178 (2013/11/19)
DMDO epoxidation of bromoallenes gives directly α,β-unsaturated carboxylic acids under the reaction conditions. Calculated (ωB97XD/6- 311G(d,p)/SCRF = acetone) potential energy surfaces and 2H- and 13C-labeling experiments are consistent with bromoallene oxide intermediates which spontaneously rearrange via a bromocyclopropanone in an intersecting bromoallene oxide-Favorskii manifold.
