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Asymmetric Organocatalysis - download pdf or read online

By Benjamin List

ISBN-10: 3642028152

ISBN-13: 9783642028151

As nucleophiles, easy alkenes tend to be so unreactive that in basic terms hugely energetic electrophiles, akin to carbocations, peroxides, and halogens will react with them. For the iteration of carbon-carbon bonds, milder tools will usually be required. thankfully, it really is attainable to extend the reactivity of alkene-type p-nucleophiles by way of introducing electron-donating substituents. Substitution of 1 H with an OH or OR provides an enol or a vinyl ether, that are already far better nucleophiles. utilizing nitrogen rather than oxygen, one obtains even higher nucleophiles, enamines. Enamines are one of the such a lot reactive impartial carbon nucleophiles, displaying premiums which are even resembling a few charged nucleophiles, resembling enolates [1, 2]. such a lot enamines, regrettably, are delicate to hydrolysis. The mother or father enamine, N, N-dimethylvinylamine, has in truth been ready [3], yet seems to be uns- ble. Enamines of cyclic ketones and lots of aldehydes can effortlessly be remoted, even though [4-7]. The instability of enamines may well at the beginning seem to cut back the application of enamines as nucleophiles, yet truly this estate could be considered as an additional benefit: enamines will be simply and speedily generated catalytically through the use of an appropriate amine and a carbonyl compound. The condensation of aldehydes or ketones with amines first and foremost offers an imine or iminium ion, which then quickly loses a proton to have the funds for the corresponding enamine (Scheme 1).

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Asymmetric Organocatalysis by Benjamin List PDF

As nucleophiles, easy alkenes tend to be so unreactive that merely hugely energetic electrophiles, reminiscent of carbocations, peroxides, and halogens will react with them. For the iteration of carbon-carbon bonds, milder tools will frequently be required. thankfully, it really is attainable to extend the reactivity of alkene-type p-nucleophiles by way of introducing electron-donating substituents.

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The best results were obtained with 139c and 139d providing 1,4-dicarbonyls 140c and 140d, respectively, in 80% yield. HO O O n H O n O 138 OAc 3 steps 137 Me Cl 139 H O S N Bn 100 mol% 74 n Et3N, EtOH, 78 oC a b c d O 140 n = 1, 50% n = 2, 66% n = 3, 80% n = 4, 80% (14) Carbene Catalysts 105 Suzuki and co-workers achieve aromatic substitution of fluoroarenes with a variety of aldehydes in good yields [91, 92]. Imidazolilydene carbene formed from 143 catalyzes the reaction between 4-methoxybenzaldehyde 22a and 4-fluoronitrobezene 141 to provide ketone 142 in 77% yield (Scheme 20).

Of 3,4-dimethyl5-(2’-hydroxyethyl) thiazolium iodide 54 and 50 equiv. of triethylamine. 3 eq 54 Et3N, i-PrOH 9 steps O MeO2C CN 149 150 5 steps HMe Me H O Me MeO2C CN MeO2C O 151 67% OH HMe O H (± )-hirsutic acid C MeO2C H 152 Scheme 22 Trost et al. synthesis of (±)-hirsutic acid C The Stetter reaction has also been shown to be an important tool in the synthesis of CI-981, also known as LIPITOR® [96]. Roth and co-workers demonstrate the ability of commercially available starting materials 153 and 154 to couple in the presence of 20 mol% thiazolium pre-catalyst 121 (Scheme 23) [97, 98].

HO O O n H O n O 138 OAc 3 steps 137 Me Cl 139 H O S N Bn 100 mol% 74 n Et3N, EtOH, 78 oC a b c d O 140 n = 1, 50% n = 2, 66% n = 3, 80% n = 4, 80% (14) Carbene Catalysts 105 Suzuki and co-workers achieve aromatic substitution of fluoroarenes with a variety of aldehydes in good yields [91, 92]. Imidazolilydene carbene formed from 143 catalyzes the reaction between 4-methoxybenzaldehyde 22a and 4-fluoronitrobezene 141 to provide ketone 142 in 77% yield (Scheme 20). Replacement of the nitro group with cyano or benzoyl results in low yields of the corresponding ketones.

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Asymmetric Organocatalysis by Benjamin List


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