- Asymmetric Cation-Olefin Monocyclization by Engineered Squalene–Hopene Cyclases
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Squalene–hopene cyclases (SHCs) have great potential for the industrial synthesis of enantiopure cyclic terpenoids. A limitation of SHC catalysis has been the enzymes’ strict (S)-enantioselectivity at the stereocenter formed after the first cyclization step. To gain enantio-complementary access to valuable monocyclic terpenoids, an SHC-wild-type library including 18 novel homologs was set up. A previously not described SHC (AciSHC) was found to synthesize small amounts of monocyclic (R)-γ-dihydroionone from (E/Z)-geranylacetone. Using enzyme and process optimization, the conversion to the desired product was increased to 79 %. Notably, analyzed AciSHC variants could finely differentiate between the geometric geranylacetone isomers: While the (Z)-isomer yielded the desired monocyclic (R)-γ-dihydroionone (>99 % ee), the (E)-isomer was converted to the (S,S)-bicyclic ether (>95 % ee). Applying the knowledge gained from the observed stereodivergent and enantioselective transformations to an additional SHC-substrate pair, access to the complementary (S)-γ-dihydroionone (>99.9 % ee) could be obtained.
- Aeberli, Natalie,Berweger, Raphael,Bornscheuer, Uwe T.,Buller, Rebecca,Dossenbach, Sandro,Eichenberger, Michael,Eichhorn, Eric,Flachsmann, Felix,Hüppi, Sean,Hortencio, Lucas,Patsch, David,Voirol, Francis,Vollenweider, Sabine
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p. 26080 - 26086
(2021/09/20)
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- Olefination via Cu-Mediated Dehydroacylation of Unstrained Ketones
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The dehydroacylation of ketones to olefins is realized under mild conditions, which exhibits a unique reaction pathway involving aromatization-driven C-C cleavage to remove the acyl moiety, followed by Cu-mediated oxidative elimination to form an alkene between the α and β carbons. The newly adopted N′-methylpicolinohydrazonamide (MPHA) reagent is key to enable efficient cleavage of ketone C-C bonds at room temperature. Diverse alkyl- and aryl-substituted olefins, dienes, and special alkenes are generated with broad functional group tolerance. Strategic applications of this method are also demonstrated.
- Dong, Guangbin,Xu, Yan,Zhou, Xukai
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supporting information
p. 20042 - 20048
(2021/12/03)
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- Enantioselective synthesis of α-ionone derivatives using an anti SN2′ substitution of functionalized zinc organometallics
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(Equation Presented) The allylic substitution of sterically hindered (2-iodocycloalkyl)phosphates proceeds with complete anti SN2′ stereoselectivity with mixed diorganozincs of the type RZnCH 2SiMe3 in the presence of CuCN·2LiCI. Only the group R of the copper-zinc reagent is transferred in the allylic substitution. This method was used to prepare odoriferous substances such as (R)-α-ionone in 97% ee and (R)-dihydro-α-ionone in 98% ee.
- Soorukram, Darunee,Knochel, Paul
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p. 2409 - 2411
(2007/10/03)
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- Preparative Bioorganic Chemistry, XV. - Preparation of Optically pure 2,4,4-Trimethyl-2-cyclohexen-1-ol, a New and Versatile Chiral Building Block in Terpene Synthesis
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Enzymatic hydrolysis of (+/-)-2,4,4-trimethyl-2-cyclohexenyl acetate with pig liver esterase yielded (R)-(+)-2,4,4-trimethyl-2-cyclohexen-1-ol and unchanged (S)-(-)-acetate (S)-3.Enantiomerically pure (S)-2 was converted into (R)-dihydro
- Mori, Kenji,Puapoomchareon, Prapai
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p. 1053 - 1056
(2007/10/02)
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