- (Poly)cationic λ3-Iodane-Mediated Oxidative Ring Expansion of Secondary Alcohols
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Herein, a simplified approach to the synthesis of medium-ring ethers through the electrophilic activation of secondary alcohols with (poly)cationic λ3-iodanes (N-HVIs) is reported. Excellent levels of selectivity are achieved for C–O bond migration over established α-elimination pathways, enabled by the unique reactivity of a novel 2-OMe-pyridine-ligated N-HVI. The resulting hexafluoroisopropanol (HFIP) acetals are readily derivatized with a range of nucleophiles, providing a versatile functional handle for subsequent manipulations. The utility of this methodology for late-stage natural product derivatization was also demonstrated, providing a new tool for diversity-oriented synthesis and complexity-to-diversity (CTD) efforts. Preliminary mechanistic investigations reveal a strong effect of alcohol conformation on the reactive pathway, thus providing a predictive power in the application of this approach to complex molecule synthesis.
- Walters, Jennifer C.,Tierno, Anthony F.,Dubin, Aimee H.,Wengryniuk, Sarah E.
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supporting information
p. 1460 - 1464
(2018/04/06)
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- Diastereoselective and enantioselective alkaline-hydrolysis of 2-aryl-1-cyclohexyl acetate: a CAL-B catalyzed deacylation/acylation tandem process
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Candida antarctica lipase proved to be a particularly efficient lipase for the resolution of racemic 2-arylcyclohexyl acetate in hydrolysis reaction with Na2CO3 in an organic medium. The (1R,2S)-trans-2-arylcyclohexanols 2a–2d were obtained with high ee values (up to >99%) and the selectivity reached E > 200. The influence of the enol ester and the solvent on (±)-trans-2-arylcyclohexanol in the CAL-B catalyzed acylation was also studied and compared with the deacylation. The CAL-B exhibits a better affinity for the alkaline hydrolysis reaction compared with acylation with the enol esters in the same organic solvents. The best conditions were applied to resolve a stereoisomeric mixture cis/trans-2-phenyl-1-cyclohexanol and its corresponding acetate by acylation and deacylation. The obtained results show a highly enantio- and diastereoselectivity of the CAL-B during the acylation and the deacylation in favor of the trans-(R)-enantiomer product. The resolution of a mixture of cis/trans-2-arylcyclohexanols was an easy, convenient approach to provide only one stereoisomer of a mixture of four with high enantiomeric excess.
- Belkacemi, Fatma Zahra,Merabet-Khelassi, Mounia,Aribi-Zouioueche, Louisa,Riant, Olivier
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supporting information
p. 1644 - 1650
(2017/10/12)
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- Directed β C-H Amination of Alcohols via Radical Relay Chaperones
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A radical-mediated strategy for β C-H amination of alcohols has been developed. This approach employs a radical relay chaperone, which serves as a traceless director that facilitates selective C-H functionalization via 1,5-hydrogen atom transfer (HAT) and enables net incorporation of ammonia at the β carbon of alcohols. The chaperones presented herein enable direct access to imidate radicals, allowing their first use for H atom abstraction. A streamlined protocol enables rapid conversion of alcohols to their β-amino analogs (via in situ conversion of alcohols to imidates, directed C-H amination, and hydrolysis to NH2). Mechanistic experiments indicate HAT is rate-limiting, whereas intramolecular amination is product- and stereo-determining.
- Wappes, Ethan A.,Nakafuku, Kohki M.,Nagib, David A.
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supporting information
p. 10204 - 10207
(2017/08/10)
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- Diastereoselective and Enantioselective Silylation of 2-Arylcyclohexanols
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The silylation-based kinetic resolution of trans 2-arylcyclohexanols was accomplished by employing a triaryl silyl chloride as the derivatizing reagent with a commercially available isothiourea catalyst. The methodology is selective for the trans diastereomer over the cis, which provides an opportunity to selectively derivatize one stereoisomer out of a mixture of four. By employing this technology, a facile, convenient method to form a highly enantiomerically enriched silylated alcohol was accomplished through a one-pot reduction-silylation sequence that started with a 2-aryl-substituted ketone.
- Wang, Li,Akhani, Ravish K.,Wiskur, Sheryl L.
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supporting information
p. 2408 - 2411
(2015/05/27)
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- Nickel-catalyzed regiodivergent opening of epoxides with aryl halides: Co-catalysis controls regioselectivity
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Epoxides are versatile intermediates in organic synthesis, but have rarely been employed in cross-coupling reactions. We report that bipyridine-ligated nickel can mediate the addition of functionalized aryl halides, a vinyl halide, and a vinyl triflate to epoxides under reducing conditions. For terminal epoxides, the regioselectivity of the reaction depends upon the cocatalyst employed. Iodide cocatalysis results in opening at the less hindered position via an iodohydrin intermediate. Titanocene cocatalysis results in opening at the more hindered position, presumably via TiIII-mediated radical generation. 1,2-Disubstituted epoxides are opened under both conditions to form predominantly the trans product.
- Zhao, Yang,Weix, Daniel J.
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supporting information
p. 48 - 51
(2014/01/23)
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- Influence of chiral thiols on the diastereoselective synthesis of γ-lactams from cyclic anhydrides
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The synthesis of γ-lactams from both four-component and imine-anhydride reactions is reported. The synthesis of 2-phenylcyclohexanethiol is described and this compound was evaluated along with an additional seven chiral thiols. A range of selectivity and yields was observed and comparisons to established reactions are made in order to account for the observed reactivity.
- Younai, Ashkaan,Fettinger, James C.,Shaw, Jared T.
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scheme or table
p. 4320 - 4327
(2012/07/28)
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- Reduction of carbonyl compounds by lanthanide metal/2-propanol: In-situ generation of samarium isopropyloxide for stereoselective Meerwein-Ponndorf- Verley reduction
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The reduction of ketones and aldehydes with lanthanide metals (La, Ce, Sm, Yb) and a catalytic amount of iodine (5 mol %) in iPrOH proceeded smoothly to produce the corresponding alcohols as the major products in good yield, while in THF, methanol, and ethanol the pinacols were mainly produced. The yields of alcohols were improved most effectively by the use of Sm metal, the amount of pinacol produced thus being minimized. The actual reducing agent may be samarium isopropyloxide, which mediates the Meerwein-Ponndorf-Verley-type hydride-transfer reaction, since the reaction can be carried out catalytically with respect to samarium. The stereoselectivities of the reductions of the 2- and 4-substituted cyclohexanones with Sm/iPrOH were higher than those achieved with SmI2/iPrOH or Sm/ H20. The asymmetric reduction of acetophenone could be achieved to give the 1-phenylethanol in up to 95% ee in the presence of the chiral ligand 7. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Fukuzawa, Shin-Ichi,Nakano, Narihito,Saitoh, Takahide
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p. 2863 - 2867
(2007/10/03)
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- The design of novel N-4′-pyridinyl-α-methyl proline derivatives as potent catalysts for the kinetic resolution of alcohols
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A novel family of chiral acylation catalysts based on a N-4′-pyridinyl-α-methyl proline structure has been studied. A set of 31 compounds has been easily prepared and screened in the kinetic resolution of racemic alcohol 33 resulting in high enantioselectivities in most cases. From results obtained, H-bonding interactions between the catalyst and the substrate would appear essential to afford high enantioselectivity during the catalytic acylation. Additional solvent dependence and anhydride studies have been made to better identify the mechanism. This work has been further extended to the study of a number of structurally different alcohols. Ethanolamine derivatives in particular were found to be highly effective substrates (up to S = 18.8) in the kinetic resolution.
- Priem, Ghislaine,Pelotier, Béatrice,Macdonald, Simon J. F.,Anson, Mike S.,Campbell, Ian B.
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p. 3844 - 3848
(2007/10/03)
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- Recyclable Polyurea-Microencapsulated Pd(0) Nanoparticles: An Efficient Catalyst for Hydrogenolysis of Epoxides
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(Matrix presented) Pd nanoparticles (~2 nm in size) microencapsulated in polyurea is an efficient and recyclable catalyst for reductive ring-opening hydrogenolysis of epoxides, using either HCOOH/Et3N or H2 as a hydrogen donor.
- Ley, Steven V.,Mitchell, Claire,Pears, David,Ramarao, Chandrashekar,Yu, Jin-Quan,Zhou, Wuzong
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p. 4665 - 4668
(2007/10/03)
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- Diastereoselective reduction of alkenylboronic esters as a new method for controlling the stereochemistry of up to three adjacent centers in cyclic and acyclic molecules
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(figure presented) cis-Boronates are readily available via a diastereoselective Pd-catalyzed reduction of tetrasubstituted alkenylboronic esters using H2. Applying the reaction conditions presented to unsaturated open-chain boronic esters allows the stereochemistry of up to three adjacent centers to be controlled.
- Hupe, Eike,Marek, Ilan,Knochel, Paul
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p. 2861 - 2863
(2007/10/03)
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- Free-radical hydroxylation reactions of alkylboronates
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The radical hydroxylation of B-alkylcatecholboranes, easily prepared by hydroboration of olefins, has been investigated. When molecular oxygen was used as oxidizing agent, the corresponding alcohols were obtained directly without alkaline treatment. The presence of Lewis base additives such as Et3N or DABCO has a benefic effect on the selectivity and yield. Alternatively, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) reacts cleanly with B-alkylcatecholboranes to afford alkyl radicals that can be trapped by a second equivalent of TEMPO to give alkoxyamines. Reduction of the alkoxyamines with zinc in acetic acid affords the desired alcohols. The whole procedure is particularly mild and does not require any basic condition. The two approaches presented in this paper are valuable and represent mild alternatives to the classical alkaline oxidation of organoboranes to alcohols.
- Cadot, Christine,Dalko, Peter I.,Cossy, Janine,Ollivier, Cyril,Chuard, Rachel,Renaud, Philippe
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p. 7193 - 7202
(2007/10/03)
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- Diastereoselective reduction of cyclohexanones with diisobutylaluminium phenoxides in terms of the isoinversion principle
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The diastereoselectivity of the reduction of 2-substituted cyclohexanones 1-6 with 4-substituted diisobutylaluminium phenoxides a-d has been investigated as a function of temperature. The high-temperature region is found to be dominated by hydride transfer, which is controlled by steric as well as electronic effects. However, at low temperatures the Meerwein-Ponndorf-Verley reaction gains in Importance. This phenomenon is quantified by an isoinversion relationship.
- Meyer-Stork, Markus A.,Haag, Dieter,Scharf, Hans-Dieter
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p. 593 - 595
(2007/10/03)
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- Asymmetric synthesis of CDP840 by Jacobsen epoxidation. An unusual syn selective reduction of an epoxide
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An asymmetric synthesis of the PDE IV inhibitor, CDP840 (3) is reported. The absolute stereochemistry was controlled by a Jacobsen epoxidation of the Z triaryl olefin 8 (89% ee) or the E triaryl olefin 9 (48% ee). The disparate results in stereocontrol were interpreted in terms of the 'skewed side-on approach model' proposed by Jacobsen. LiBH4 · BH3 reduction of the epoxides was found to proceed with retention of configuration.
- Lynch,Choi,Churchill,Volante,Reamer,Ball
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p. 9223 - 9228
(2007/10/03)
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- Silica Gel Supported Zinc Borohydride. A Novel Reagent for Hydration of Unactivated Alkenes and Alkynes
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A simple and general procedure for hydration of unactivated alkenes and alkynes producing less substituted alcohols selectively has been achieved by the reaction of the corresponding alkenes or alkynes on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu, Brindaban C.,Sarkar, Arunkanti,Saha, Manika,Chakraborty, Rupak
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p. 6579 - 6584
(2007/10/02)
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- An Unusual Anti-Markovnikov Hydration of Alkenes with Titanium(III) Tetrahydroborates
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Titanium(III) tetrahydroborate formed by the reaction of titanium tetrachloride and benzyltriethylammonium borohydride (1:4) reacts with alkenes in dichloromethane (-20 deg C) very readily to yield directly the corresponding alcohols in excellent yields after a simple aqueous work up.
- Kumar, K. S. Ravi,Baskaran, S.,Chandrasekaran, S.
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p. 171 - 174
(2007/10/02)
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- An unusual regioselctive anti-Markovnikov hydration of alkenes with zinc borohydride on silica gel support
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An efficient and general procedure of regioselective anti-Markovnikov hydration of alkenes producing less-substituted alcohols has been achieved by a simple reaction of alkene on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu,Chakraborty,Saha
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p. 4659 - 4662
(2007/10/02)
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- An Internally Activated Tin Hydride with Enhanced Reducing Ability
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Tin hydride 1 is activated for nucleophilic hydride transfer and also for radical chain reduction, depending on solvent.The nucleophilic hydride pathway is favored in methanol, and 1 can be used as a selective reducing agent for ketones.Simple ketones are not reduced in aprotic solvents, but β-hydroxy ketones are activated internally by the hydroxyl group and can be reduced in THF with good control of stereochemistry, as in the conversion from 7 to 9 (30:1 9:8).A catalytic version of the nucleophilic hydride reductions in methanol has been developed using PhSiH3 as the stoichiometric hydride source.Radical chain dehalogenations can also be achieved with 1 at room temperature and without added radical initiators.Simple xanthates are not reduced efficiently in the absence of an initiator, but the reaction proceeds in the presence of AIBN.
- Vedejs, E.,Duncan, S. M.,Haight, A. R.
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p. 3046 - 3050
(2007/10/02)
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- A Facile Conversion of Alkenes to Alcohols with Benzyltriethylammonium Borohydride-Chlorotrimethylsilane
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A combination of benzyltrimethylammonium borohydride and chlorotrimethylsilane (1:1) in dichloromethane at 0 deg C has been found to be a convenient reagent system for the conversion of alkenes to alcohols, the hydroxy group of which is introduced in an anti-Markovnikov manner.
- Baskaran, Sundarababu,Gupta, Varsha,Chidambaram, Nallaperumal,Chandrasekaran, Srinivasan
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p. 903 - 904
(2007/10/02)
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- Solvolysis of cis- and trans-2-Phenylcyclohexyl-p-bromobenzene Sulphonate
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Die Solvolyse von cis- and trans-2-Phenyl-cyclohexyl-p-brombenzensulfonaten wurde in Essigsaeure, waessrigem Dioxan und waessrigem Ethanol untersucht und mit der des Cyclohexylsulfonatesters verglichen.In Essigsaeure liegt die Geschwindigkeit des cis-Isomeren gegenueber dem trans-Isomeren um den Faktor 5 hoeher, in waessrigem Dioxan und waessrigem Alkohol dagegen um den Faktor 10 bzw. 12.Produkte der Acetolyse sind hauptsaechlich Eliminierungsprodukte (1- und 3-Phenylcyclohexen 75 percent) und cis- und trans-Acetate (25 percent).In waessrigen Loesungsmitteln entstehen vorwiegend Eliminierungsprodukte (98 percent).Die Erhoehung der Geschwindigkeit des cis-Isomeren gegenueber der trans-Verbindung ist auf eine sterische Beschleunigung zurueckzufuehren.Ein solvatisiertes Ionenpaar wurde als Zwischenprodukt postuliert; fuer eine Phenylnachbargruppenwirkung ergab sich kein Hinweis.
- Youssef, Abdel-Hamid A.,Sharaf, Saber M.,Hegazy, Fatma M. El
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p. 725 - 734
(2007/10/02)
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- Properties of Bis(trifluoroacetoxy)borane as a Reducing Agent of Organic Compounds
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Reactions of bis(trifluoroacetoxy)borane-THF (1) with compounds containing representative organic functional groups were studied to determine the usefulness of 1 as a selective reducing agent.Reducible functionalities were indoles, ketones, aldehydes, imines, and compounds that readily generate carbocations in trifluoroacetic acid.Many functionalities were inert to 1.Epoxides and ortho esters suffered decomposition under the reaction conditions.Olefins and acetylenes were not hydroborated, and carboxylic acids were not reduced by 1.
- Maryanoff, Bruce E.,McComsey, David F.,Nortey, Samuel O.
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p. 355 - 360
(2007/10/02)
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- Formation of Alcohols from Alkenes with TiCl4-NaBH4
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The reaction of alkenes with TiCl4-NaBH4 in 1,2-dimethoxyethane afforded alcohols, the hydroxy group of which was introduced in an anti-Markovnikov direction.
- Kano, Shinzo,Tanaka, Yasuyuki,Hibino, Satoshi
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p. 414 - 415
(2007/10/02)
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