Allenic Alcohols Research Articles

Cascade Catalysis Through Bifunctional Lipase Metal Biohybrids for the Synthesis of Enantioenriched O-Heterocycles from Allenes.

Lipase/metal nanobiohybrids, generated by growth of silver or gold nanoparticles on protein matrixes are used as highly effective dual‐activity heterogeneous catalysts for the production of enantiomerically enriched 2,5‐dihydrofurans from allenic acetates in a one‐pot cascade process combining a lipase‐mediated hydrolytic kinetic resolution with a metal‐catalyzed allene cycloisomerization. Incorporating a novel strategy based on enzyme‐polymer bioconjugates in the nanobiohybrid preparation enables excellent conversions in the process. Candida antarctica lipase B (CALB) in combination with a dextran‐based polymer modifier (DexAsp) proved to be most efficient when merged with silver nanoparticles. A range of hybrid materials were produced, combining Ag or Au metals with Thermomyces lanuginosus lipase (TLL) or CALB and its DexAsp or polyethyleneimine polymer bioconjugates. The wider applicability of the biohybrids is demonstrated by their use in allenic alcohol cyclizations, where a variety of dihydrofurans are obtained using a CALB/gold nanomaterial. These results underline the potential of the nanobiohybrid catalysis as promising approach to intricate one‐pot synthetic strategies.

Cu-catalyzed, Mn-mediated propargylation and allenylation of aldehydes with propargyl bromides

A simple, practical, and high chemo-selective method for the synthesis of propargyl alcohol and allenyl alcohols via Cu-catalyzed, Mn-mediated propargylation and allenylation of aldehydes with propargyl bromides has been established. When 3-bromo-1-propyne was conducted under the standard condition, the aldehydes were transformed to the corresponding propargylation products completely, while when 1-bromo-2-pentyne was used, allenic alcohol was the only product. Variety of homopropargyl alcohols and allenyl alcohols were obtained in high yields and the reaction is compatible with broad substrate scopes. In addition, the large-scale reaction could also be proceeded smoothly indicating the potential synthetic applications of this transformation.Graphical

Radical modulated regioselective difunctionalization of vinyl enynes: tunable access to naphthalen-1(2H)-ones and allenic alcohols.

A novel and efficient radical-modulated difunctionalization of vinyl enynes has been disclosed using TEMPO as a radical regulator. Facile access to structurally diverse 3-bromo-naphthalen-1(2H)-ones and 4-bromo-allenic alcohols was realized via 1,2-addition/1,2-migration or 1,4-addition, respectively. This protocol represents the first example of radical-modulated metal-free difunctionalization of 1,3-enynes with high regioselectivity.

Visible-Light-Induced 1,4-Hydroxysulfonylation of Vinyl Enynes with Sulfonyl Chlorides: The Bridge of Chloride Linking Water and Enynes

A novel visible-light-induced 1,4-hydroxysulfonylation of vinyl enynes with sulfonyl chlorides has been established, providing a highly efficient protocol to access multisubstituted sulfonyl allenic alcohols. Control experiments and mechanistic studies disclose that the target products result from sequential reactions of hydroxyl and tosyl radicals, among which chloride anion plays a key role to generate the requisite •OH, thus bridging water and enynes. Moreover, the vinyl pendant is believed to decisively affect the site-selectivity of hydroxyl radical.

Palladium-catalyzed C-P cross-coupling of allenic alcohols with H-phosphonates leading to 2-phosphinoyl-1,3-butadienes.

The first facile, efficient, atom-economical and regioselective palladium-catalyzed direct C-P cross-coupling of unprotected allenic alcohols with H-phosphonates for the one-pot synthesis of structurally diverse multisubstituted 2-phosphinoyl-1,3-butadienes was developed. This strategy would enrich the allene chemistry and afford new scaffolds to construct complex molecular skeletons.

Arylative Allenol Cyclization via Sequential One‐pot Enzyme & Palladium Catalysis

AbstractThe one‐pot combination of halogenation biocatalysis and Suzuki‐type cross coupling enables the direct arylative cyclization of allenic alcohols with boronic acids. This modular approach to unsaturated five‐membered O‐heterocycles proceeds in an aqueous emulsion with air as terminal oxidant. Here, the enzymatic oxidative activation of simple halide salts acts as traceless ring‐closure‐inducing event to trigger the subsequent C−C coupling. With the original protocol merging soluble proteins and a homogeneous SPhos‐based palladium catalyst as a template, a novel heterogeneous nanobiohybrid was developed. Consisting of an oxidase matrix hosting small spherical palladium nanoparticles, this enzyme‐metal hybrid exhibits catalytic competence for both the biocyclization as well as the C−C bond‐forming cross coupling, underlining the potential of this new techniques for streamlining chemoenzymatic approaches.

Lithiation of 1-alkynyl-1-chlorocyclopropanes and subsequent reactions with electrophilic reagents: synthesis of functionalized alkynyl- and vinylidenecyclopropanes

1-Alkynyl-1-chlorocyclopropanes undergo chlorine-lithium exchange on treatment with BunLi in THF at -40—0 °C. Thus generated organolithium species react with carbon dioxide (dry ice) and acetone to give selectively hitherto unknown 1-alkynylcyclopropanecarboxylic acids and the corresponding alcohols in up to 74% yields. Similar reactions involving methyl chloroformate result in the mixtures of cyclopropylacetylenic and vinylidenecyclopropanic esters, while the use of aliphatic aldehydes as electrophiles provides secondary allenic alcohols in up to 64% yields.

Enantioselective Allenylation of Aldehydes via Brønsted Acid Catalysis

AbstractAn enantioselective allenylation of aldehydes catalyzed by a chiral, nonracemic phosphoric acid was reported. Under the developed conditions, 1,1′‐disubstituted allenic alcohols were obtained in 64–98% yields with 88–99% ee. Computational studies were conducted to probe the origin of asymmetric induction. Mechanistic studies suggest that the pinacol moiety of the propargylboronate is critical to the enantioselectivity of the reaction that was supported by experimental data.magnified image

Rhodium‐Catalyzed Arylative Transformations of Propargylic Diols: Dual Role of the Rhodium Catalyst

AbstractControllable synthesis of a variety of allenic alcohols and 2,5‐dihydrofurans by rhodium(I)‐catalyzed arylative transformations of propargylic diols is reported. The hydroxorhodium catalyst was found to play dual role: it catalyzed the arylation/dehydroxylation reaction of propargylic diols to afford allenic alcohols, and besides, it could convert to a cationic rhodium species in situ, which catalyzed the intramolecular hydroalkoxylation of allenic alcohols to form dihydrofurans. Remarkably, generation of the cationic rhodium species is dependent on the arylboron reagent used. Thus, the controllable synthesis is achieved by simply changing the arylboron reagent.magnified image

Palladium-catalyzed three-component reaction for the synthesis of 3,3-disubstituted allylic alcohols with regio- and stereoselectivity

A novel three-component assembly of allenic alcohols, aryl iodides and 1,3-dicarbonyl compounds into 3,3-disubstituted allylic alcohols was promoted in the presence of a palladium source.

3,3]-Sigmatropic rearrangement of allenic alcohols: stereoselective synthesis of 1,3-diene-2-ol sulfonates.

An efficient synthetic pathway to 1,3-diene-2-ol sulfonates involving the [3,3]-sigmatropic rearrangement of allenic alcohols with sulfonic acids under mild reaction conditions is described. These products can easily undergo reduction or transition-metal catalyzed cross-coupling reactions to yield a series of stereodefined multisubstituted 1,3-dienes.

Enzymatic halocyclization of allenic alcohols and carboxylates: a biocatalytic entry to functionalized O-heterocycles

Chloroperoxidase (C. fumago) catalyzes the aerobic halogenative 5-endo-trig cyclization of allenes in an aqueous emulsion system yielding functionalized O-heterocyclic building blocks.

Convergent Synthesis of the Dihydropyran Core Containing the C1-C15 Subunit of Sorangicin A Employing Gold(I)-Catalyzed Cyclization of an Allenic Alcohol.

A convergent route to the C1-C15 subunit of sorangicin A is disclosed. The key steps include carbon-carbon bond formation using an α-chloro sulfide, regioselective hydrozirconation of an internal alkyne for the preparation of a trisubstituted iodoalkene, allene formation using the Myers-Movassaghi protocol, stereoselective reduction of allylic and propargylic ketones using Noyori's catalyst, and gold(I)-catalyzed cyclization of a β-hydroxy allene to construct the dihydropyran ring.

ChemInform Abstract: Enantioselective Desymmetrization of Prochiral Allenic Diols via Cooperative Catalysis of Pd(OAc)2 and a Chiral Phosphoric Acid.

AbstractThe title reaction allows the preparation of optically active disubstituted dihydrofurans (II) through Pd‐mediated 5‐endo‐trig cyclization of allenic alcohols (I).

Highly stereoselective kinetic resolution of α-allenic alcohols: an enzymatic approach

A highly efficient lipase AK-catalyzed direct kinetic resolution of a variety of α-allenic alcohols was developed. With the complementary to previous studies, the current reaction system is effective on a broad range of substituents (R1) at C(1), such as alkyl, aryl, alkenyl, and alkynyl groups. The Jones–Burgess empirical model was modified to interpret the reversed selectivity during the acetylation of secondary alcohol. The methyl group at C(2) of allenic alcohols implied a small structural adjustment in the catalytic triad of lipase AK, representing a potential direction for future site-directed mutagenesis.

Versatile PdTe/C catalyst for liquid-phase oxidations of 1,3-butadiene

A commercial Pd catalyst based on Sibunit carbon support was treated with H6TeO6 in a reducing media to obtain a Te coating on the surface of Pd particles. The PdTe/C catalyst prepared in this way showed the ability to control the radical chain oxidation of 1,3-butadiene by promoting the selective formation of 2-butene-1,4-diol, 4-hydroxybut-2-enal and furan in DMA (total selectivity of 61% and yield of 7%). At the same time, the catalyst induced oxidation of 1,3-butadiene by a non-radical heterolytic mechanism involving the formation of two groups of primary products: (1) сrotonaldehyde and methyl vinyl ketone and (2) the products of oxygenation at the 1,4-positions. The compounds of the second group including 1,4-dimethoxy-2-butene and maleic acid dimethyl ester were formed on PdTe centers in MeOH. Increasing the Te concentration in the PdTe/C catalyst forced the conversion of 1,3-butadiene toward 1,4-oxygenation and simultaneously decreased the intensity of secondary oxidation, resulting in the selective formation of derivatives of the 1,4-oxygenation—1,4-dimethoxy-2-butene and allenic alcohol methyl ether (total selectivity of 84% and yield of 48%).

Enantioselective desymmetrization of prochiral allenic diols via cooperative catalysis of Pd(OAc)2 and a chiral phosphoric acid

The first non-enzymatic desymmetrization of prochiral allenic diols via cooperative binary catalysis of Pd(OAc)2 and (R)-STRIP has been reported. This method allows easy access to a series of optically active disubstituted dihydrofurans through palladium mediated 5-endo-trig cyclizations of allenic alcohol with high yields and good to excellent enantioselectivity. A broad substrate scope has been demonstrated.

Synthesis of (−)‐Deoxynupharidine by Allenic Hydroxylamine Cyclisation

Abstract(−)‐Deoxynupharidine has been synthesised via an intermediate that can also be used for other Nuphar alkaloids. Significant steps include the optimised enzymatic resolution of an allenic alcohol, highly diastereoselective silver‐catalysed cyclisation of an allenic hydroxylamine, selective cross‐metathesis, diastereoselective intramolecular reductive amination, and stereoelectronically controlled enolate alkylation.

ChemInform Abstract: Total Synthesis of (‐)‐HM‐3 (Ia) and (‐)‐HM‐4 (Ib) Utilizing a Palladium‐Catalyzed Addition of an Arylboronic Acid to an Allenic Alcohol Followed by Eschenmoser—Claisen Rearrangement.

ChemInform Abstract: Total Synthesis of (‐)‐HM‐3 (Ia) and (‐)‐HM‐4 (Ib) Utilizing a Palladium‐Catalyzed Addition of an Arylboronic Acid to an Allenic Alcohol Followed by Eschenmoser—Claisen Rearrangement.

Total Synthesis of (–)-HM-3 and (–)-HM-4 Utilizing a Palladium-Catalyzed Addition of an Arylboronic Acid to an Allenic Alcohol Followed by Eschenmoser–Claisen Rearrangement

The first asymmetric total synthesis of (–)-HM-3 and (–)-HM-4, aromatic sesquiterpenes isolated from the phytopathogenic fungus Helicobasidium mompa, has been achieved. Highlight of the synthesis is an enantiospecific construction of the quaternary carbon stereocenter utilizing a palladium-catalyzed addition of arylboronic acid to the allenic alcohol followed by Eschenmoser–Claisen rearrangement.