Highly stereoselective synthesis of trisubstituted olefins via addition of alkylcopper complexes to acetylenes

Heterogeneous Copper-Catalyzed Cross-Coupling for Sustainable Synthesis of Chiral Allenes: Application to the Synthesis of Allenic Natural Products

Classical Crabbé type SN 2' substitutions of propargylic substrates has served as one of the standard methods for the synthesis of allenes. However, the stereospecific version of this transformation often requires either stoichiometric amounts of organocopper reagents or special functional groups on the substrates, and the chirality transfer efficiency is also capricious. Herein, we report a sustainable methodology for the synthesis of diverse 1,3-di and tri-substituted allenes by using a simple and cheap cellulose supported heterogeneous nanocopper catalyst (MCC-Amp-Cu(I/II)). This approach represents the first example of heterogeneous catalysis for the synthesis of chiral allenes. High yields and excellent enantiospecificity (up to 97 % yield, 99 % ee) were achieved for a wide range of di- and tri-substituted allenes bearing various functional groups. It is worth noting that the applied heterogeneous catalyst could be recycled at least 5 times without any reduced reactivity. To demonstrate the synthetic utility of the developed protocol, we have applied it to the total synthesis of several chiral allenic natural products.

(E)-α-Iodovinylstannanes as Convenient Precursors for Stereoselective Synthesis of Trisubstituted Alkenes

Based on the different reactivities of iodo-groups and tributylstannyl groups, ( E)-α-iodovinylstannanes can undergo sequential cross-coupling reactions in the presence of a palladium(0) catalyst to form two carbon-carbon bonds to the same olefinic carbon leading to trisubstituted alkenes stereoselectively.

Direct, catalytic, and regioselective synthesis of 2-alkyl-, aryl-, and alkenyl-substituted N-heterocycles from N-oxides

A one-step transformation of heterocyclic N-oxides to 2-alkyl-, aryl-, and alkenyl-substituted N-heterocycles is described. The success of this broad-scope methodology hinges on the combination of copper catalysis and activation by lithium fluoride or magnesium chloride. The utility of this method for the late-stage modification of complex N-heterocycles is exemplified by facile syntheses of new structural analogues of several antimalarial, antimicrobial, and fungicidal agents.

Aggregation pheromone of square-necked grain beetle,Cathartus quadricollis (Guér.)

When feeding on rolled oats, male square-necked grain beetles,Cathartus quadricollis (Guér.), produced the aggregation pheromone (3R,6E)-7-methyl-6-nonen-3-yl acetate, for which the trival name "quadrilure" is proposed. The pheromone was highly attractive to both sexes in a two-choice, pitfall olfactometer modified to retain responding beetles by placing a food stimulus (an oat flake) in the glass vials containing the experimental and control stimuli. TheS enantiomer of the pheromone was inactive. Males also produced small amounts of (E)-7-methyl-6-nonen-3-one, (E)-7-methyl-6-nonen-3-ol, and (6E)-7-methyl-3-propyl-2,6-nonadienyl acetate, but these compounds were inactive in the laboratory bioassay. Segregated males and females both produced (R)-(-)-1-octen-3-ol, which by itself was repellent to both sexes but did not diminish beetle response to the aggregation pheromone.

Exploration of an epoxidation-ring-opening strategy for the synthesis of lyconadin A and discovery of an unexpected Payne rearrangement

In the context of synthetic efforts targeting the alkaloid lyconadin A, scalemic epoxide 25 was prepared by a highly stereoselective sequence involving a Myers alkylation and a Shi epoxidation. Ring-opening of this epoxide with a vinylcopper complex afforded alcohol 26 instead of the expected product 27. An unusual Lewis acid promoted Payne rearrangement of an α-trityloxy epoxide is proposed to account for this outcome.

Alkyne elementometalation-Pd-catalyzed cross-coupling. Toward synthesis of all conceivable types of acyclic alkenes in high yields, efficiently, selectively, economically, and safely: "green" way

Palladium-catalyzed cross-coupling reactions, especially those involving Zn, Al, Zr (Negishi coupling), and B (Suzuki coupling), collectively have brought about "revolutionary" changes in organic synthesis. Thus, two regio- and stereodefined carbon groups generated as R(1)M (M = Zn, Al, B, Cu, Zr, etc.) and R(2)X (X = I, Br, OTs, etc.) may now be cross-coupled to give R(1)-R(2) with essentially full retention of all structural features. For alkene syntheses, alkyne elementometalation reactions including hydrometalation (B, Al, Zr, etc.), carbometalation (Cu, Al-Zr, etc.), and haloboration (BX(3) where X is Cl, Br, and I) have proven to be critically important. Some representative examples of highly efficient and selective (>or=98%) syntheses of di-, tri-, and oligoenes containing regio- and stereodefined di- and trisubstituted alkenes of all conceivable types will be discussed with emphasis on those of natural products. Some interesting but undesirable cases involving loss of the initial structural identities of the alkenyl groups are attributable to the formation of allylpalladium species, which must be either tamed or avoided. Some such examples involving the synthesis of 1,3-, 1,4-, and 1,5-dienes will also be discussed.

A One-Pot, Stereoselective Synthesis of (Z)-1,2-disubstituted Vinyl Sulfides by Sequential Hydrostannylation and Stille reaction of Acetylenic Sulfides with Tributyltin Hydride and then with aryl iodides

( Z)-1,2-Disubstituted vinyl sulfides can be stereoselectively synthesised in one pot under mild conditions, in good yields, by the palladium-catalysed hydrostannylation of acetylenic sulfides, followed by Stille coupling with aryl iodides.

Stereoselective Synthesis of (Z)-α-Arylsulfenylvinyl Tellurides Via Hydrozirconation of Alkynyltellurides

Hydrozirconation of alkynyltellurides 1 in THF at room temperature gave ( Z)-α- tellurenylvinylzirconium complexes 2, which were reacted with arylsulfenyl chlorides 3 to afford stereoselectively ( Z)-α-arylsulfenylvinyl tellurides 4 in good yields.

Organic Reactions in Water: An Efficient Zinc-Mediated Stereoselective Synthesis of (E)- and (Z)-Trisubstituted Alkenes Using Unactivated Alkyl Halides

[reaction: see text] Treatment of the acetyl derivatives of the Baylis-Hillman adducts 3-hydroxy-2-methylene-alkanoates and 3-hydroxy-2-methylene-alkanenitriles with unactivated alkyl halides in the presence of Zn in saturated aqueous NH(4)Cl solution at room temperature afforded (2E)-2-substituted-alk-2-enoates in the first case and (2Z)-2-substituted-alk-2-enenitriles with high (Z)-selectivity in the second case.

Stereoselective Synthesis of (E)-α-Silylvinyl Tellurides via the Hydrozirconation Reaction of Alkynylsilanes

( E)-α-silylvinyl tellurides have been synthesised stereoselectively via the hydrozirconation of alkynylsilanes, followed by reaction with aryltellurenyl iodides. ( E)-α-Silylvinyl tellurides can undergo cross coupling reaction with Grignard reagents in the presence of [NiCl2(PPh3)2] catalyst to give ( Z)-1,2-disubstituted vinylsilanes in good yields.

First highly stereoselective synthesis of fungicide systhane

[reaction: see text] Highly enantiopure (R)-2-p-chlorophenyl-2-(1H-1,2,4-triazol-1-ylmethyl)hexanenitrile 1 (myclobutanil or systhane) was obtained in six synthetic steps from commercially available 1-hexyne (35% yield, 92% ee). The sulfinyl group controls the two key steps of the synthetic sequence, the highly stereoselective hydrocyanation of vinyl sulfoxides with Et(2)AlCN and the further introduction of the proper functionality into the molecule.

Synthesis of Methoxynor Polyisoprenoid Alcohols by Alkylation of (3-Methoxyallyl)lithium Reagents

A series of six methyl enol ether analogs 8-13 of geraniol, (E,E)-farnesol, and (E,E,E)-geranylgeraniol was synthesized from a group of three allylic methyl ethers and three allylic chlorides. Lithiation of the 1-methyl-, or 1-alkenylvinyl ethers with sec-butyllithium at -78 °C followed by alkylations of the resulting (Z)-(3-methoxyallyl)lithium reagents afforded the six possible Z-configured(trans) methoxynor polyprenyl benzyl ethers bearing the methoxy substituent at the internal and terminal double bonds with high Z/E ratios (5 : 1-31 : 1) and 47-80% yields. Reductive cleavage of the benzyl groups with lithium in liquid ammonia gave the corresponding methoxynor polyprenols. 11-Methoxy-18-nor and 7-methoxy-19-nor geranylgeraniols (13 and 12) were converted to the corresponding diphosphates, 7 and 32, by the Poulter displacement method. The stability of the enol ether in 7 in aqueous solution at pH 8 was verified by NMR analyses. The diphosphates of the methoxynor polyprenols may prove useful as substrate analogs for terpene synthases to capture transient intermediates in cyclization reactions catalyzed by these enzymes.