Conjugate Reduction Of Enones Research Articles

Catalytic Hydrogenations with Cationic Heteroleptic Copper(I)/N-Heterocyclic Carbene Complexes

A new heteroleptic cationic copper(I) complex bearing two N-heterocyclic carbene (NHC) ligands has been prepared. In situ, a Cu–O­ bond can be generated which enables the complex to catalytically activate H2. The resulting complex shows activity in catalytic chemo- and stereoselective alkyne semihydrogenations as well as conjugate reductions of enones.

PMHS‐Containing Semi‐Penetrating Networks as Multifunctional Hydrosilanes for Highly Efficient Palladium‐Catalyzed Conjugate Reduction of Enones

AbstractThe polymethylhydrosiloxane (PMHS)–containing organosilicon materials (PMHS‐SIPNs) was proved to be a useful reducing agent and palladium support in the conjugate reductions of various α,β–unsaturated ketones, providing a direct and effective route to a variety of substituted ketones. In addition, the PMHS‐SIPNs–derived palladium catalyst was shown to be recyclable up to 5 times without any observable decrease in yield and efficiency, and it exhibited low metal leaching under the mild reaction conditions. The resulting heterogeneous palladium catalyst in this reaction featured with easy preparation, facile recovery and reuse, and high selectivity.

Diastereo‐ and Enantioselective Reductive Aldol Reaction with Trichlorosilane Using Chiral Lewis Bases as Organocatalysts

The catalytic enantioselective tandem reaction is an efficient synthetic methodology in which optically active compounds are assembled from simple prochiral substrates via two (or more) distinct catalytic processes taking place under the same conditions. The synthetic efficiency is enhanced by avoiding the time-intensive and yield-reducing isolation and purification of synthetic intermediates and by decreasing the amounts of chemicals and solvents used. The asymmetric catalytic reductive aldol reaction is an efficient tandem transformation involving conjugate reduction of a,b-unsaturated carbonyl compounds followed by aldol reaction of the enolate intermediate with aldehydes or ketones. Chiral transition-metal catalysts have been used to control the stereochemistry of these transformations. We recently reported that achiral phosphorus oxides function as Lewis base organocatalysts to promote both the conjugate reduction of enones with trichlorosilane and the reductive aldol reaction of enones with aldehydes. Herein we report that enantioselective catalysis of this tandem reaction by chiral Lewis bases provides good to high diastereoand enantioselectivities. Scheme 1 outlines the current catalytic method. Our previous study had shown that the Lewis base catalyzed conjugate reduction with trichlorosilane proceeds via a six-membered transition state with an enone in the s-cis conformation to give the (Z)-trichlorosilyl enolate exclusively. Therefore, high syn selectivity is expected for the subsequent aldol process, assuming that the reaction proceeds through a chair-like cyclic transition state. Moreover, high enantioselectivity could also be achieved by judicious selection of chiral Lewis base catalysts (LB*). We first examined various chiral Lewis base catalysts (Figure 1) for the reductive aldol reaction of chalcone (1a) and benzaldehyde (2a) with trichlorosilane at 78 8C (Table 1). With (S)-BINAPO, the reaction in dichloromethane gave aldol adduct 3a with respectable stereoselectivities (Table 1, entry 1). By simply changing the solvent from dichloromethane to propionitrile, both the stereoselectivities and chemical yield dramatically improved (Table 1, entry 2). Other Lewis base catalysts were then examined using this solvent (Table 1, entries 3–6). (R,R)-DIOPO showed a comparable activity to BINAPO to afford similar enantioselectivity with a slight loss of diastereoselectivity (Table 1, entry 3). Although structurally similar to BINAPO, (S)[a] Prof. Dr. M. Sugiura, N. Sato, Y. Sonoda, Prof. Dr. M. Nakajima Graduate School of Pharmaceutical Sciences Kumamoto University 5-1 Oe-honmachi, Kumamoto 862-0973 (Japan) Fax: (+81)96-362-7692 E-mail : msugiura@kumamoto-u.ac.jp (M. Sugiura) nakajima@gpo.kumamoto-u.ac.jp (M. Nakajima) [b] Prof. Dr. S. Kotani Priority Organization for Innovation and Excellence Kumamoto University 5-1 Oe-honmachi, Kumamoto 862-0973 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.200900450. Scheme 1. The enantioselective reductive aldol reaction with trichlorosilane catalyzed by a chiral Lewis base catalyst.

Palladium‐Catalyzed Conjugate Reduction of Enones into α,β‐Dideuterioketones with Hexamethyldisilane and Deuterium Oxide.

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Palladium-Catalyzed Enantioselective Conjugate Reduction of Enones

Palladium-Catalyzed Enantioselective Conjugate Reduction of Enones

Mechanism and stereochemistry of conjugate reduction of enones from gibberellins A3 and A7

Conjugate reduction of the methyl esters of 3-didehydrogibberellin A3 13-acetate and of 3-didehydrogibberellin A7, in aprotic solvents by borohydride (or borodeuteride), is shown to introduce hydrogen (or deuterium) at the 1β- and 3β-positions in the products, 3-epi-gibberellin A1 13-acetate and 3-epi-gibberellin A4 methyl esters. The third hydrogen (or deuterium) comes from the proton (or deuteron) source used in the work-up. A mechanism for conjugate reduction of enones is proposed. The products from the borodeuteride reduction of 3-didehydrogibberellin A7 methyl ester with proton and deuteron work-up were chemically converted into [1β-2H1]-, [1β,22H2]-, and [1β3α-2H2]-gibberellin A4 and the stereochemistries of the deuterium atoms were determined from the deuterium content of the metabolites, formed from these labelled gibberellins in cultures of Gibberella fujikuroi, mutant B1-41a.