13080-90-5Relevant articles and documents
Stereoselective [4+2]-Cycloaddition with Chiral Alkenylboranes
Brown, M. Kevin,Houk, K. N.,Ni, Dongshun,Witherspoon, Brittany P.,Zhang, Hong,Zhou, Chen
supporting information, p. 11432 - 11439 (2020/05/18)
A method for the stereoselective [4+2]-cycloaddition of alkenylboranes and dienes is presented. This transformation was accomplished through the introduction of a new strategy that involves the use of chiral N-protonated alkenyl oxazaborolidines as dieneophiles. The reaction leads to the formation of products that can be readily derivatized to more complex structural motifs through stereospecific transformations of the C?B bond such as oxidation and homologation. Detailed computation evaluation of the reaction has uncovered a surprising role of the counterion on stereoselectivity.
Alkylhalovinylboranes: a new class of Diels-Alder dienophiles
Pisano, Pablo L.,Pellegrinet, Silvina C.
, p. 33864 - 33871 (2018/10/20)
The Diels-Alder reactions of alkylhalovinylboranes have been investigated theoretically and experimentally. Alkylhalovinylboranes presented higher reactivity than the corresponding dialkylvinylboranes. Although endo/exo selectivities were high for the reactions with cyclopentadiene, facial selectivities for the chiral analogues were low. Our results demonstrate that the replacement of an alkyl group on the boron atom by a halogen increases the dienophilicity considerably.
α-Hydroxyacids accelerate the Diels-Alder reaction of dibutyl vinylboronate with cyclopentadiene: Experimental results and mechanistic insights
Grimblat,Sarotti,Pisano,Pellegrinet
, p. 1966 - 1969 (2016/03/22)
We have found that α-hydroxyacids accelerate the Diels-Alder reaction of dibutyl vinylboronate with cyclopentadiene. When stoichiometric quantities are used, excellent yields are obtained, while catalytic activities are moderate. DFT calculations suggested that the activation of the dienophile occurs by ligand exchange with both functionalities of the α-hydroxyacid.
Diels-Alder reactions of pinacol alkenylboronates: An experimental and theoretical study
Vallejos, Margarita M.,Grimblat, Nicolas,Pellegrinet, Silvina C.
, p. 36385 - 36400 (2014/12/09)
We have studied the Diels-Alder reactions of pinacol alkenylboronates with cyclopentadiene under two different sets of conditions: thermal heating at 170 °C in a pressure tube and with catalytic TFA (5 mol%) at 80 °C. Yields varied significantly from system to system and also for the uncatalyzed and catalyzed methodologies. Moderate to excellent exo-stereoselectivities were obtained in all cases. The theoretical study of the thermal reactions sheds some light on the intriguing substituent effects observed experimentally. A variety of substituted 5-norbornen-2-ols were easily generated by subsequent in situ oxidation of the cycloadducts with alkaline hydrogen peroxide. This journal is the Partner Organisations 2014.
A facile microwave-assisted Diels-Alder reaction of vinylboronates
Sarotti, Ariel M.,Pisano, Pablo L.,Pellegrinet, Silvina C.
supporting information; experimental part, p. 5069 - 5073 (2010/12/25)
The Diels-Alder reaction of vinylboronates can be easily performed using microwave irradiation giving excellent yields of the cycloadducts. Pinacol vinylboronate was the reagent of choice due to its stability towards hydrolysis, operational simplicity and yields of Diels-Alder products. To the best of our knowledge, this is the first example of microwave-assisted Diels-Alder reaction of boron-substituted dienophiles. Subsequent in situ oxidation of the cycloadducts with alkaline hydrogen peroxide afforded the alcohols efficiently.
Stereoselectivity in the rhodium-catalysed reductions of nonconjugated dienes
Nguyen, Bao,Brown, John M.
supporting information; experimental part, p. 1333 - 1343 (2009/12/27)
The stereochemical course of rhodium-catalysed addition of hydrogen and catecholborane to bicyclo[2.2.1]heptadiene, and of hydrogen to a range of cyclic dienes has been analysed. For hydroboration, the overall catalytic reaction possesses exo-selectivity, but the initial step is endo-selective. For hydrogenation (deuteration), the first step may occur with either exo- or endo- selectivity, depending on the structure of the diene. This enables a distinction to be made between pathways involving prior dissociation of the diene, and direct addition to the complexed diene without full dissociation. The relative ease of hydrogenation of the first and second doublebonds varies markedly with reactant structure, and also depends on the choice of catalyst ligands. For dicyclopentadiene, hydrogenation of the cyclopentene double bond is accompanied by rapid alkene isomerisation, as revealed by deuterium addition. The asymmetric hydrogenation of acyclic skipped mesodienes is reported, demonstrating control of relative rates of the two sequential steps, with ees of up to 53% after the first reduction.
Design of very transparent fluoropolymer resists for semiconductor manufacture at 157 nm
Feiring, Andrew E.,Crawford,Farnham,Feldman,French,Leffew,Petrov,Schadt III,Wheland,Zumsteg
, p. 11 - 16 (2007/10/03)
Photolithography at 157 nm requires development of new photoresists that are highly transparent at this wavelength. Transparent fluoropolymer platforms have been identified which also possess other materials properties required for chemically amplified imaging and aqueous development. Polymers of tetrafluoroethylene (TFE), a fluoroalcohol-substituted norbornene and an acid-labile acrylate ester show the best combination of properties. A solution, semibatch, free-radical polymerization process was developed allowing synthesis of the terpolymers on a multikilogram scale. Further property enhancements may arise from replacing the norbornene with functionalized tricyclononenes. Formulated resists have been imaged in a 157 nm microstepper.
Ring-opening metathesis - Cross-metathesis reactions (ROM-CM) of substituted norbornadienes and norbornenes
Mayo, Peter,Tam, William
, p. 9513 - 9525 (2007/10/03)
Ring-opening metathesis - cross-metathesis reactions (ROM-CM) of substituted norbornadienes and norbornenes were investigated. The reactions with symmetrical 2,3-disubstituted norbornadienes were found to be highly chemoselective, with the ROM reactions occurring only on the less substituted or less sterically hindered double bonds regardless of the electronic nature of the substituents, giving highly substituted cyclopentenes in moderate to good yields. This study provides an efficient method for the stereoselective synthesis of highly substituted cyclopentenoids. Long-range electronic effect of a remote substituent on unsymmetrical norbornenes in the ROM-CM reactions was also investigated. Low levels of regioselectivities were observed (50:50 to 69:31) with various remote substituents on the norbornenes.
Remote substituent effects on the oxymercuration of 2-substituted norbornenes: An experimental and theoretical study
Mayo,Orlova,Goddard,Tam
, p. 5182 - 5191 (2007/10/03)
The effect of a remote substituent on regioselectivity in the oxymercuration of 2-substituted norbornenes has been investigated experimentally and theoretically using density functional theory (DFT). Regioselectivities of 1:1 to 14:1 were observed with various 2-substituted norbornenes. Exo-2-substituted norbornenes always gave greater regioselectivities compared to the corresponding endo-2-substituted norbornenes. The effects of solvents on the regioselectivity have also been examined, and ethereal solvents were found to be the best choice giving the optimal yield and regioselectivity. The relative rate of oxymercuration was estimated by competition experiments. The least reactive substrate (X = OAc) gave the highest regioselectivity. According to DFT predictions, the increased difference between the reaction barriers that results in the greater regioselectivity is correlated directly with the larger polarity of the C=C double bond, which is attacked by the mercury and oxygen. A number of stable exo and endo conformers were predicted. All exo conformers show the same polarity of the double bond, while some endo conformers have a reversal of this polarity. All the conformers except those with the OAc substituent are very close in energy and thus should react. The existence of a mixture of endo conformers with the C=C double bond of opposite polarity clearly explains a decrease in regioselectivity for the endo species. The origin of the greatest regioselectivity for the OAc-2-norbornenes lies in the fact that the conformer with the largest polarity is notably lower in energy than others due to an internal C-H-O hydrogen bond.
Convenient Enzymatic Resolution of Alcohols Using Highly Reactive, Nonharmful Acyl Donors, 1-Ethoxyvinyl Esters
Kita, Yasuyuki,Takebe, Yasushi,Murata, Kenji,Naka, Tadaatsu,Akai, Shuji
, p. 83 - 88 (2007/10/03)
1-Ethoxyvinyl esters 3, a new type of acyl donors for enzymatic resolution of racemic alcohols, were disclosed to be superior to the contemporary major reagents, vinyl esters 1 and isopropenyl esters 2. Three features of 3 are noticeable: (1) 3 generates ethyl acetate as a single coproduct, which does not affect any enzymes, while acetaldehyde liberated from 1 deactivates some kinds of lipases. (2) The reactivity of 3 was not less than that of 1 and much higher than that of 2, and the optical purity of the products was as high as that of 1 and 2. Especially, it was generally observed that 3 showed higher reactivity than 1 for reactions using Candida rugosa lipases, one of the most commonly employed lipases, having liberal applicability to substrates but sensitive to acetaldehyde. Twelve examples of the kinetic resolution of racemic secondary alcohols (5 and 10) and one desymmetrization of meso-alcohol 7 were presented employing the acetate 3a or the octanoate 3b and four types of lipases. (3) A one-pot procedure for the preparation of 3 from the corresponding carboxylic acid and the subsequent enzymatic resolution of alcohols, which has not been reported using 1 or 2, was elucidated. The chemical and optical yields of the products by this procedure were similar to those obtained using isolated 3.
