Rhenium-Catalyzed 1,3-Isomerization of Allylic Alcohols: Scope and Chirality Transfer

Secondary allylic alcohols were synthesized from linear allylic halides or carbonates using a catalytic amount of a ruthenium complex in the presence of boronic acid. The effects of solvent, base, ruthenium precursor, and boronic acid were fully explored, and the scope of the reaction was extended to various substrates. We also describe a preliminary investigation towards an enantioselective process.

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“…(E)-3-(2-Nitrophenyl)prop-2-en-1-ol: [18,36] (E)-3-(3-Nitrophenyl)prop-2-en-1-ol: [37] 97 %. (E)-3-(4-Nitrophenyl)prop-2-en-1-ol: [18,39] 98 %.…”

Section: Methodsunclassified

Ruthenium‐Catalyzed Synthesis of Allylic Alcohols: Boronic Acid as a Hydroxide Source

Bouziane

Hélou

Carboni

et al. 2008

Chemistry A European J

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“…In some cases, the use of acyl donors with a longer alkyl chain, such as vinyl butyrate and vinyl decanoate, produced higher enantioselectivities (entries 5- 7, 9, 13, and 14). Moreover, it was applicable to benzyl 1 q, furyl 1 r, and propargyl alcohols 1 s to give 3 q-s in excellent yield and enantioselectivity, whereas the previous conditions using 4 or 5 [6] were relatively ineffective (entries [17][18][19]. Optically pure (R)-3 n, the key synthetic intermediate of (+)-tanikolide, which employed the less expensive cyclohexenone as the starting material, was produced in twice the previously obtained yield (entry 14).…”

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confidence: 99%

A Mesoporous‐Silica‐Immobilized Oxovanadium Cocatalyst for the Lipase‐Catalyzed Dynamic Kinetic Resolution of Racemic Alcohols

Egi¹,

Sugiyama²,

Saneto³

et al. 2013

Angew Chem Int Ed

103

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In the last decade, cooperative catalysis has received considerable attention as a powerful synthetic method. [1] Two or more catalysts function simultaneously or sequentially in a single reaction vessel to construct complicated molecules, which provides a means to perform unprecedented syntheses that cannot be achieved by a single catalyst. Various catalytic combinations involving transition metals, organocatalysts, and biocatalysts have been developed thus far. [2] A typical example is the combined use of lipases and transition metals to attain the dynamic kinetic resolution (DKR) of racemic secondary alcohols for producing single enantiomer products in up to 100 % yields, [3] in contrast to the use of lipases alone, which can only achieve maximum yields of 50 %. In this DKR process, the enzymatic enantioselective esterification of racemic alcohols is combined with the transition-metal-catalyzed continuous racemization of optically active alcohols, which remain intact during the enzymatic reaction, through a redox process. However, such cooperative cocatalysis often encounters crucial issues of low compatibility between the lipases and the transition metals. Although intense efforts have been devoted to developing highly active racemization catalysts, [4, 5] only a few ruthenium complexes have met both the requirement of sufficient compatibility with lipases and high racemization activity. [5] We recently reported that a combination of oxovanadium compounds (4 or 5) with lipases accomplished the efficient and direct conversion of racemic allylic alcohols (AE)-1 and (AE)-2 into optically active allyl esters (R)-3. [6] This method featured a unique racemization process wherein 4 (or 5) catalyzed the racemization of (S)-1 with 1,3-transposition of the hydroxy group of 1 or 2, while the lipases effected chemoand enantioselective esterification. This is significantly different from the above-mentioned ruthenium-catalyzed DKRs and offered a synthetic advantage in that both (AE)-1 and (AE)-2 were available as equivalent substrates. However, this method required further improvement in both catalytic activity and compatibility of the oxovanadium catalysts with the lipases. [7,8] Herein, we report the preparation of a novel oxovanadium catalyst (V-MPS) immobilized inside mesoporous silica (MPS) with pores of approximately 3 nm in diameter, which enabled a complete division of the racemization site and the enzymatic reaction site. The combined lipase-V-MPS catalyst is reusable and achieved DKR of a wide range of racemic alcohols with excellent chemical and optical yields (Scheme 1).The immobilization of oxovanadium species inside a solid carrier with microsized pores or multilayered structures [9] enables the minimization of interactions between the oxovanadium species and lipases while maintaining easy access of substrate molecules to the metal center. The solid carrier should be neutral and non-charged in order to exert little adverse effect on the lipases. Among the various potential solid carriers, [10,11] MPS,...

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“…Grubbs studied Osborn's reaction and found that O 3 ReOSiPh 3 isomerizes allylic alcohols stereospecifically 3. Both Osborn and Grubbs invoked a concerted [3,3] rearrangement of allylic perrhenate esters to explain this very facile and selective isomerization (Figure 1).…”

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“…Osborn proposed an ionic mechanism to explain the kinetics for formation of Z -alkenes,2b and Grubbs invoked a similar mechanism to explain the loss of optical purity with certain electron-rich allylic alcohol substrates (Figure 1). 3 The proposed ionic mechanism attracted our attention because it suggested that Re(VII) complexes might activate and solvolyze electron rich alcohols. We report herein a Prins cyclization initiated by Re(VII) catalysts4 based on this concept that is both very mild and shows unusual selectivity.…”

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confidence: 99%

Rhenium(VII) Catalysis of Prins Cyclization Reactions

Tadpetch

Rychnovsky

2008

Org. Lett.

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The rhenium(VII) complex O 3 ReOSiPh 3 are particularly effective catalyst for Prins cyclizations using aromatic and α,β-unsaturated aldehydes. The reaction conditions are mild and the highly substituted 4-hydroxy tetrahydropyran products are formed stereoselectively. Rhenium(VII) complexes appear to spontaneously form esters with alcohols and to directly activate electron rich alcohols for solvolysis. Re 2 O 7 and perrhenic acid were equally effective in catalyzing these cyclizations.Osborn reported that the Re(VII) complex O 3 ReOSiPh 3 1 was a highly effective catalyst for allylic alcohol isomerizations. 2 Grubbs studied Osborn's reaction and found that O 3 ReOSiPh 3 isomerizes allylic alcohols stereospecifically. 3 Both Osborn and Grubbs invoked a concerted [3,3] rearrangement of allylic perrhenate esters to explain this very facile and selective isomerization ( Figure 1). 2,3 An alternative mechanism was invoked to explain some of the peculiarities of the reaction. Osborn proposed an ionic mechanism to explain the kinetics for formation of Z-alkenes, 2b and Grubbs invoked a similar mechanism to explain the loss of optical purity with certain electron-rich allylic alcohol substrates (Figure 1). 3 The proposed ionic mechanism attracted our attention because it suggested that Re(VII) complexes might activate and solvolyze electron rich alcohols. We report herein a Prins cyclization initiated by Re(VII) catalysts 4 based on this concept that is both very mild and shows unusual selectivity.Prins cyclization reactions between homoallylic alcohols and aldehydes are generally promoted by strong Bronsted or Lewis acids. 5 If halide counterions are present, they are incorporated at the 4-position of the newly formed tetrahydropyran (THP) ring. 5 Oxygen atoms can be captured at the 4-position of the THP ring, 6 although most acids lead to esters that must be hydrolyzed to form 4-hydroxy THP products. 7 Most Prins cyclizations use superstoichiometric acid to promote the reaction because the acid counterion is trapped in the product, thus consuming the acid. Cyclization and trapping leads to perrhenate ester 6. Ester exchange with Ph 3 SiOH would regenerate the catalyst. The proposed Re(VII) initiated reaction has several potential advantages over traditional Prins cyclization reactions. It avoids the use of strong acid, and the facile transesterification of perrhenate esters with alcohols allows turnover and makes the system catalytic. Additionally, the alcohol product would be produced directly from the reaction rather than requiring a subsequent hydrolysis step. These potentially attractive features led us to explore this reaction. Table 1 presents an initial exploration of the Re(VII) catalyzed Prins cyclization. The aldehyde and homoallylic alcohol were selected with the same substituent to avoid complications from oxonia-Cope induced side-chain exchanges. 8 O 3 ReOSiPh 3 catalyzed the Prins cyclization effectively in most solvents except acetonitrile. Although the reaction was effective using 1 mol % cata...

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Rhenium-Catalyzed 1,3-Isomerization of Allylic Alcohols: Scope and Chirality Transfer

Cited by 69 publications

References 65 publications

Ruthenium‐Catalyzed Synthesis of Allylic Alcohols: Boronic Acid as a Hydroxide Source

Ruthenium‐Catalyzed Synthesis of Allylic Alcohols: Boronic Acid as a Hydroxide Source

A Mesoporous‐Silica‐Immobilized Oxovanadium Cocatalyst for the Lipase‐Catalyzed Dynamic Kinetic Resolution of Racemic Alcohols

Rhenium(VII) Catalysis of Prins Cyclization Reactions

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