- (Z)-Selective Hydroboration of Terminal Alkynes Catalyzed by a PSP-Pincer Rhodium Complex
-
A highly (Z)-selective hydroboration of terminal alkynes was achieved using a thioxanthene-based PSP-pincer rhodium catalyst. This hydroboration exhibited good chemoselectivity toward alkynes over carbonyl compounds such as ketones and aldehydes. The mechanistic studies indicated the involvement of rhodium-vinylidene intermediates, and the high (Z)-selectivity could be attributed to the rigid and electron-rich nature of the PSP-rhodium catalyst.
- Lyu, Yanzong,Toriumi, Naoyuki,Iwasawa, Nobuharu
-
supporting information
p. 9262 - 9266
(2021/11/30)
-
- Aliphatic α-Boryl-α-bromoketones: Synthesis and Reactivity
-
A protocol for the preparation of α-boryl-α-bromoketones from alkenyl MIDA boronates was developed and applied to functionalized aliphatic derivatives. The reaction sequence included regioselective hydroxybromination of olefin moiety, followed by oxidation of alcohol group with Dess–Martin periodinane. The target trifunctional boronate-containing derivatives were obtained in up to 94 % yield over two steps starting from alkenyl MIDA boronates. In some cases, functional groups present in the substrate participated in the bromohydroxylation step via intramolecular nucleophilic attack at the bromonium cation leading to cyclic products. Additionally, the reactivity of aliphatic α-boryl-α-bromoketones was illustrated by nucleophilic substitution at the α-C atom and heterocyclization reactions.
- Ivon, Yevhen M.,Kuchkovska, Yuliya O.,Voitenko, Zoya V.,Grygorenko, Oleksandr O.
-
p. 3367 - 3377
(2020/03/13)
-
- Stereoselective Bromoboration of Acetylene with Boron Tribromide: Preparation and Cross-Coupling Reactions of (Z)-Bromovinylboronates
-
The mechanism of acetylene bromoboration in neat boron tribromide was studied carefully by means of experiment and theory. Besides the syn-addition mechanism through a four-center transition state, radical and polar anti-addition mechanisms are postulated, both triggered by HBr, which is evidenced also to take part in the Z/E isomerization of the product. The proposed mechanism is well supported by ab initio calculations at the MP2/6-31+G? level with Ahlrichs' SVP all-electron basis for Br. Implicit solvation in CH2Cl2 has been included using the PCM and/or SMD continuum solvent models. Comparative case studies have been performed involving the B3LYP/6-31+G? with Ahlrichs' SVP for Br and MP2/Def2TZVPP levels. The mechanistic studies resulted in development of a procedure for stereoselective bromoboration of acetylene yielding E/Z mixtures of dibromo(bromovinyl)borane with the Z-isomer as a major product (up to 85%). Transformation to the corresponding pinacol and neopentyl glycol boronates and stereoselective decomposition of their E-isomer provided pure (Z)-(2-bromovinyl)boronates in 57-60% overall yield. Their reactivity in a Negishi cross-coupling reaction was tested. An example of the one-pot reaction sequence of Negishi and Suzuki-Miyaura cross-couplings for synthesis of combretastatin A4 is also presented.
- Polá?ek, Jan,Paciorek, Jan,Sto?ek, Jakub,Semrád, Hugo,Munzarová, Markéta,Mazal, Ctibor
-
p. 6992 - 7000
(2020/06/05)
-
- ISOMERIZATION OF ALKENES
-
The present invention relates to an isomerization method for alkenes, comprising of reaction an alkene with a Ni(I)-compound. By this method, E-Alkenes are obtained in excellent yield.
- -
-
Page/Page column 20-21; 23
(2020/04/25)
-
- Ru-catalyzed isomerization of ω-alkenylboronates towards stereoselective synthesis of vinylboronates with subsequent: In situ functionalization
-
The stereoselective preparation of synthetically versatile vinylboronates from ω-alkenylboronates is achieved through a ruthenium-catalyzed isomerization reaction. A variety of di- A nd trisubstituted vinylboronates were conveniently produced and could be
- Ho, Guo-Ming,Marek, Ilan,Segura, Lucas
-
p. 5944 - 5949
(2020/07/10)
-
- E-Olefins through intramolecular radical relocation
-
Full control over the selectivity of carbon-carbon double-bond migrations would enable access to stereochemically defined olefins that are central to the pharmaceutical, food, fragrance, materials, and petrochemical arenas. The vast majority of double-bond migrations investigated over the past 60 years capitalize on precious-metal hydrides that are frequently associated with reversible equilibria, hydrogen scrambling, incomplete E/Z stereoselection, and/or high cost. Here, we report a fundamentally different, radical-based approach.We showcase a nonprecious, reductant-free, and atom-economical nickel (Ni)(I)-catalyzed intramolecular 1,3-hydrogen atom relocation to yield E-olefins within 3 hours at room temperature. Remote installations of E-olefins over extended distances are also demonstrated.
- Kapat, Ajoy,Sperger, Theresa,Guven, Sinem,Schoenebeck, Franziska
-
p. 391 - 396
(2019/02/03)
-
- Enantioselective Conjunctive Cross-Coupling of Bis(alkenyl)borates: A General Synthesis of Chiral Allylboron Reagents
-
Palladium-catalyzed conjunctive cross-coupling is used for the synthesis of enantioenriched allylboron reagents. This reaction employs nonsymmetric bis(alkenyl)borates as substrates and appears to occur by a mechanism that involves selective activation of the less substituted alkene followed by migration of the more substituted alkene during the course of a Pd-induced metalate rearrangement.
- Edelstein, Emma K.,Namirembe, Sheila,Morken, James P.
-
supporting information
p. 5027 - 5030
(2017/05/04)
-
- Enantioselective syn and anti homocrotylation of aldehydes: Application to the formal synthesis of spongidepsin
-
Whereas crotylboration has been a useful method for synthesis of stereochemically complex products, we have shown that homocrotylboration can be achieved with cyclopropanated crotylation reagents, and that the stereoselectivity of the reaction can be predicted by analogous models. This paper presents a full account of this work, including the first examples of asymmetric anti homocrotylation. The scope of this reaction is demonstrated with highly enantioselective homocrotylation of both aliphatic and aromatic aldehydes, as well as double diastereoselection studies. An application of the synthesis of the marine natural product spongidepsin is presented, as well as streamlined syntheses of homocrotylation reagents.
- Lin, Hongkun,Tian, Leiming,Krauss, Isaac J.
-
supporting information
p. 13176 - 13182
(2015/10/28)
-
- Double-Bond Isomerization: Highly Reactive Nickel Catalyst Applied in the Synthesis of the Pheromone (9 Z,12 Z)-Tetradeca-9,12-dienyl Acetate
-
A highly reactive nickel catalyst comprising NiCl2(dppp) or NiCl2(dppe) with zinc powder, ZnI2 and Ph2PH, was applied in the isomerization of terminal alkenes to Z-2-alkenes. The double-bond geometry of the 2-alkene can be controlled via the reaction temperature to yield the 2-Z-alkenes in excellent yields and high Z-selectivities. The formation of other constitutional isomers, such as 3-alkenes, is suppressed on the basis of the proposed mechanism via a 1,2-hydride shift from the metal to the Ph2P ligand. The nickel-catalyzed isomerization reaction was then applied in the synthesis of (9Z,12Z)-tetradeca-9,12-dienyl acetate, a pheromone with a 2Z,5Z-diene subunit.
- Weber, Felicia,Schmidt, Anastasia,R?se, Philipp,Fischer, Michel,Burghaus, Olaf,Hilt, Gerhard
-
supporting information
p. 2952 - 2955
(2015/06/30)
-
- Enantiospecific, regioselective cross-coupling reactions of secondary allylic boronic esters
-
An original syn: The first enantioselective Suzuki-Miyaura cross-coupling of chiral, enantioenriched secondary allylic boronic esters is described (see scheme; DME=dimethoxyethane, Bpin = pinacolboryl, dba = dibenzylideneacetone). Mechanistic studies show that the reactions proceed via γ-selective transmetalation followed by reductive elimination. The reaction provides the first independent confirmation that the transmetalation of boronic esters proceeds via a syn pathway. Copyright
- Chausset-Boissarie, Laetitia,Ghozati, Kazem,Labine, Emily,Chen, Jack L.-Y.,Aggarwal, Varinder K.,Crudden, Cathleen M.
-
supporting information
p. 17698 - 17701
(2014/01/17)
-
- Z -selective homodimerization of terminal olefins with a ruthenium metathesis catalyst
-
The cross-metathesis of terminal olefins using a novel ruthenium catalyst results in excellent selectivity for the Z-olefin homodimer. The reaction was found to tolerate a large number of functional groups, solvents, and temperatures while maintaining excellent Z-selectivity, even at high reaction conversions.
- Keitz, Benjamin K.,Endo, Koji,Herbert, Myles B.,Grubbs, Robert H.
-
supporting information; experimental part
p. 9686 - 9688
(2011/08/05)
-
- AMINO HETEROARYL COMPOUNDS AS BETA-SECRETASE MODULATORS AND METHODS OF USE
-
The present invention comprises a new class of compounds useful for the modulation of Beta-secretase enzyme activity and for the treatment of Beta-secretase mediated diseases, including Alzheimer?s disease (AD) and related conditions. In one embodiment, the compounds have a general Formula I wherein ring A, B1, B2, B3, L, R1, R4, R5 and m of Formula I are defined herein. The invention also includes use of these compounds in pharmaceutical compositions for treatment, prophylactic or therapeutic, of disorders and conditions related to the activity of beta-secretase protein. Such disorders include, for example, Alzheimer?s Disease (AD), cognitive deficits, cognitive impairment, schizophrenia and other central nervous system conditions related to and/or caused by the formation and/or deposition of plaque on the brain. The invention also comprises further embodiments of Formula I, intermediates and processes useful for the preparation of compounds of Formula I
- -
-
Page/Page column 68
(2011/06/19)
-
- Application of the lithiation-bborylation reaction to the preparation of enantioenriched allylic boron reagents and subsequent in situ conversion into 1,2,4-trisubstituted homoallylic alcohols with complete control over all elements of stereochemistry
-
The reactions of Hoppe's lithiated carbamates with vinylboranes and boronic esters give allylic boranes/boronic esters, and subsequent addition of aldehydes provides a new route to enantioenriched homoallylic alcohols with high enantiomeric ratios and diastereomeric ratios. Specifically, reactions of sparteine-complexed lithiated carbamates with frans-alkenyl-9-BBN derivatives followed by addition of aldehydes gave (Z)-anti-homoallylic alcohols in greater than 95:5 er and 99:1 dr. However, in the special case of the methyl-substituted lithiated carbamate, diamine-free conditions were required to achieve high selectivity. Reactions of sparteine-complexed lithiated carbamates with (2)-alkenyl pinacol boronic esters and (E)-alkenyl neopentyl boronic esters gave (E)-syn- and (E)-anti-homoallylic alcohols, respectively, in greater than 96:4 er and 98:2 dr. In these reactions, a Lewis acid (MgBr2 or BF 3·OEt2) was required to promote both the 1,2-metalate rearrangement and the addition of the intermediate allylic boronic ester to the aldehyde. This methodology provides a general route to each of the three classes of homoallylic alcohols with high selectivity.
- Althaus, Martin,Mahmood, Adeem,Suarez, Jose Ramon,Thomas, Stephen P.,Aggarwal, Varinder K.
-
supporting information; experimental part
p. 4025 - 4028
(2010/05/14)
-
- Diastereoselective addition of zincated hydrazones to alkenylboronates and stereospecific trapping of boron/zinc bimetallic intermediates by carbon electrophiles
-
Zincated hydrazones possessing a tert-butyl group on the zinc atom undergo addition to (E)- or (Z)-alkenylboronic acid pinacol esters to produce α-alkylated-γ-boryl-γ-zinciohydrazone intermediates with good to excellent diastereoselectivity (ds). The 1,1 -organodimetallic intermediate possessing a boron atom and a zinc atom in the position γ to the hydrazone group undergoes further C-C bond formation with a carbon electrophile to give a γ-boryl hydrazone possessing several contiguous stereogenic centers with up to 99% ds. The (S)-1-amino-2-methoxymethylpyrrolidine hydrazone shows a high level of asymmetric induction in the addition/trapping sequence. Density functional theory calculations on the pathways of the addition reaction revealed a metallo-ene mechanism consisting of the formation of a π complex between a zincated hydrazone and a vinylborane followed by a six-centered bond reorganization of a highly ordered boat conformation transition state. The calculations indicated that the use of the zinc atom together with the imine or hydrazone is the key for the success of the olefinic variant of the aldol reaction that has long been considered not to take place because of the endothermicity of the reaction and has never been examined with any seriousness by chemists. The steric repulsion caused by the bulky tert-butyl ligand on the zinc atom and the pinacol moiety of the vinylboronate substrates in the highly ordered transition structures gives rise to the observed high ds of the present carbozincation reaction.
- Hatakeyama, Takuji,Nakamura, Masaharu,Nakamura, Eiichi
-
supporting information; experimental part
p. 15688 - 15701
(2009/03/12)
-
- Sequential coupling of zincated hydrazone, alkenylboronate, and electrophile that creates several contiguous stereogenic centers
-
A zincated N,N-dimethylhydrazone of a ketone undergoes stereospecific syn addition to E- or Z-alkenylboronate to generate a γ-Zn/B dimetallic intermediate, which reacts with a carbon electrophile to give a γ-borylhydrazone in good yield with excellent dia
- Nakamura, Masaharu,Hatakeyama, Takuji,Hara, Kenji,Fukudome, Hiroki,Nakamura, Eiichi
-
p. 14344 - 14345
(2007/10/03)
-
- Synthesis of functionalized vinyl boronates via ruthenium-catalyzed olefin cross-metathesis and subsequent conversion to vinyl halides
-
Functionalized vinyl pinacol boronates suitable for Suzuki cross-coupling reactions are synthesized using ruthenium-catalyzed olefin cross-metathesis of 1-propenyl pinacol boronate and various alkenes, including functionalized and 1,1-disubstituted alkenes. The resultant boronate cross products are stereoselectively transformed into predominantly Z-vinyl bromides and E-vinyl iodides. The vinyl bromides may be synthesized in a two-step, one-pot synthesis from a variety of olefins, resulting in a Z-selective formal vinyl bromide cross-metathesis reaction.
- Morrill, Christie,Grubbs, Robert H.
-
p. 6031 - 6034
(2007/10/03)
-