- A Concise Synthesis of rac-Ambrox via the Palladium(0)-Catalyzed Carboalkoxylation of an Allylic Ammonium Salt, as Compared to a Formaldehyde Hetero Diels–Alder Approach
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Acidic cyclization of either the diethylallylamines 29b or 30, followed by a 1.5 mol-% Pd-catalyzed carbomethoxylation of quaternized 31b, leads to the methyl ester 36a. This latter could also be obtained in optically pure form by carbomethoxylation of the corresponding (+)-acetate. Final reduction-cyclization may be conducted as earlier described, towards the desired odoriferous rac-Ambrox 38a, or its pure (?)-enantiomer. Generation of a π-allyl Pd complex from an allylic ammonium salt, followed by carboalkoxylation is novel. In only five chemical steps starting from farnesene 2, the present work constitutes the most concise total synthesis of rac-Ambrox 38a to date.
- Chapuis, Christian,Skuy, David,Richard, Claude-Alain
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- Tungsten-catalyzed asymmetric epoxidation of allylic and homoallylic alcohols with hydrogen peroxide
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A simple, efficient, and environmentally friendly asymmetric epoxidation of primary, secondary, tertiary allylic, and homoallylic alcohols has been accomplished. This process was promoted by a tungsten-bishydroxamic acid complex at room temperature with the use of aqueous 30% H2O2 as oxidant, yielding the products in 84-98% ee.
- Wang, Chuan,Yamamoto, Hisashi
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supporting information
p. 1222 - 1225
(2014/02/14)
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- Iron-catalyzed intramolecular allylic C-H amination
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A highly selective C-H amination reaction under iron catalysis has been developed. This novel system, which employs an inexpensive, nontoxic [Fe IIIPc] catalyst (typically used as an industrial ink additive), displays a strong preference for allylic C-H amination over aziridination and all other C-H bond types (i.e., allylic > benzylic > ethereal > 3° > 2° ? 1°). Moreover, in polyolefinic substrates, the site selectivity can be controlled by the electronic and steric character of the allylic C-H bond. Although this reaction is shown to proceed via a stepwise mechanism, the stereoretentive nature of C-H amination for 3° aliphatic C-H bonds suggests a very rapid radical rebound step.
- Paradine, Shauna M.,White, M. Christina
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supporting information; scheme or table
p. 2036 - 2039
(2012/03/11)
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- Microbial synthesis of optically pure (R)-2,4,4-trimethyl-3-(2'-hydroxyethyl)-cyclohex-2-en-1-ol, a new and versatile chiral building block for terpene synthesis
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The hydroxylation of 2,4,4-trimethyl-3-(2'-hydroxyethyl)-2-cyclohexene by Mucor plumbeus, after usual work up and a subsequent single crystallization, gave the corresponding optically pure (1R)-hydroxy synthon.
- Aranda,Bertranne,Azerad,Maurs
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p. 675 - 678
(2007/10/02)
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- Fermentation of Fragrances: Biotransformation of β-Ionone by Lasiodiplodia theobromae
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Pre-grown mycelia of Lasiodiplodia theobromae ATCC 28570 transform β-ionone (1) into a large variety of metabolites, by mainly degrading the side-chain of the β-ionone molecule by a C2-unity.The enzyme system responsible for this degradation is proposed to be an oxygenase, which gives rise to the formation of the main product β-cyclo-homogeraniol (8) in analogy to a Baeyer-Villiger oxidation.Further enzymic actions of Lasiodiplodia such as hydrogenations and hydroxylations lead to an accumulation of several not yet described β-ionone metabolites.
- Krasnobajew, Victor,Helmlinger, Daniel
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p. 1590 - 1601
(2007/10/02)
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