Vinylcopper Species Research Articles

Copper‐Catalyzed and Proton‐Directed Selective Hydroxymethylation of Alkynes with CO2

AbstractAn intriguing strategy for copper‐catalyzed hydroxymethylation of alkynes with CO2 and hydrosilane was developed. Switched on/off a proton source, for example, tBuOH, direct hydroxymethylation and reductive hydroxymethylation could be triggered selectively, delivering a series of allylic alcohols and homobenzylic alcohols, respectively, with high levels of Z/E, regio‐ and enantioselectivity. Such a selective synthesis is attributed to the differences in response of vinylcopper intermediate to proton and CO2. The protonation of vinylcopper species is demonstrated to be prior to hydroxymethylation, thus allowing a diversion from direct alkyne hydroxymethylation to reductive hydroxymethylation in the presence of suitable proton.

Copper-Catalyzed and Proton-Directed Selective Hydroxymethylation of Alkynes with CO2.

An intriguing strategy for copper-catalyzed hydroxymethylation of alkynes with CO2 and hydrosilane was developed. Switched on/off a proton source, for example, t BuOH, direct hydroxymethylation and reductive hydroxymethylation could be triggered selectively, delivering a series of allylic alcohols and homobenzylic alcohols, respectively, with high levels of Z/E, regio- and enantioselectivity. Such a selective synthesis is attributed to the differences in response of vinylcopper intermediate to proton and CO2 . The protonation of vinylcopper species is demonstrated to be prior to hydroxymethylation, thus allowing a diversion from direct alkyne hydroxymethylation to reductive hydroxymethylation in the presence of suitable proton.

Synthesis of Substituted Cyclopentenol Derivatives via Intramolecular Addition Reaction of Vinylcopper Species

A new method for the synthesis of substituted cyclopentenes is developed, based on an intramolecular 1,2-addition reaction of vinylcopper species generated from 1,1-dibromoalkene derivatives. The substrates are prepared from ketones through the aldol reaction with 3,3-dibromoacrolein followed by silylation of the hydroxyl group. Treatment of the substrate with excess Me2CuLi results in the formation of 3-methyl-2-cyclopenten-1-ol derivatives with good yields.

Asymmetric Total Synthesis of Brasilicardins

Brasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti-syn-anti-fused perhydrophenanthrene terpenoid scaffold (ABC-ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC-ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)-vinyl copper species. The late-stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A-D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Asymmetric Total Synthesis of Brasilicardins

AbstractBrasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti‐syn‐anti‐fused perhydrophenanthrene terpenoid scaffold (ABC‐ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC‐ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)‐vinyl copper species. The late‐stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A–D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Cu(III)–CF3 Complex Enabled Unusual (Z)-Selective Hydro-trifluoromethylation of Terminal Alkynes

An efficient and selective hydro-trifluoromethylation of terminal alkynes is developed to enable the synthesis of 1,2-disubstituted trifluoromethylated Z-alkenes from terminal alkynes, a silane and a Cu(III)-CF3 complex in DMF. The unusual Z-selectivity and the compatibility of various functional groups make this reaction complementary to previous vinyl-CF3 bond-forming methods producing dominantly E-products or a mixture of E, Z-isomers. Extensive mechanistic studies indicate that this reaction may involve a key step of migratory insertion of initially formed Ar-C≡C-CF3 into LCu(I)-H intermediate and subsequent hydrogenation of the vinyl-copper species to give finally the Z-trifluoromethylated styrenes. Deuterium labeling experiments show that DMF acts not merely as the solvent but also as the source of α-H in the Z-trifluoromethylated styrene products. Given the novel syn-difunctionalization of alkynes using Cu(III)-CF3 complexes/a nucleophilic reagent we developed recently that are also in contrast to the previous anti-difunctionalization chemistry, Cu(III)-CF3 complexes are demonstrated to show distinct reactivity properties compared to conventional CF3 reagents (Togni's reagents and Umemoto-type reagents) and may thus enable the development of other interesting reactions.

Regio- and stereoselective carbometallation reactions of N-alkynylamides and sulfonamides

The carbocupration reactions of heterosubstituted alkynes allow the regio- and stereoselective formation of vinyl organometallic species. N-Alkynylamides (ynamides) are particularly useful substrates for the highly regioselective carbocupration reaction, as they lead to the stereodefined formation of vinylcopper species geminated to the amide moiety. The latter species are involved in numerous synthetically useful transformations leading to valuable building blocks in organic synthesis. Here we describe in full the results of our studies related to the carbometallation reactions of N-alkynylamides.

ChemInform Abstract: Synergistic Effect of Palladium and Copper Catalysts: Catalytic Cyclizative Dimerization of ortho‐(1‐Alkynyl)benzamides Leading to Axially Chiral 1,3‐Butadienes.

AbstractThe concurrent formation of vinylpalladium and vinylcopper species followed by transmetalation is the key feature in the Pd/Cu co‐catalyzed cyclizative dimerization of the alkynes (I) and (III).

Synthesis of Alicyclic Esters via an Intramolecular Conjugate Addition Reaction. New Method for Generating (Z)‐Vinylcopper Species from 1,1‐Dibromoalkenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

(Z)-Vinylcopper Species from 1,1-Dibromoalkenes and its Reactions

(<i>Z</i>)-Vinylcopper Species from 1,1-Dibromoalkenes and its Reactions

Synthesis of alicyclic esters via an intramolecular conjugate addition reaction. New method for generating ( Z)-vinylcopper species from 1,1-dibromoalkenes

A novel cyclization reaction of a 1,1-dibromoalkene derivative having an α,β-unsaturated ester moiety was developed. Under the influence of Me 2CuLi, the 1,1-dibromoalkene was converted into a ( Z)-vinylcopper species which in turn underwent an intramolecular conjugate addition reaction with the α,β-unsaturated ester moiety. Five-, six-, and seven-membered carbocycles were constructed by the present method. The substrate having an epoxide moiety also afforded a five-membered product via a 5- exo type intramolecular cyclization reaction.

Allylic phosphates and allylic phosphinates as electrophiles in efficient silylcupration reactions of acetylenes.

Atom-efficient stoichiometric silylcupration reactions of acetylenes followed by electrophilic trapping of the intermediate vinylcopper species with allylic phosphates have been developed. The reaction sequence was also carried out with the use of a catalytic amount of CuCN employing of both allylic phosphates and allylic phosphinates as electrophiles. The methods developed provide an easy access to silylated 1,4-diene systems.

A tandem allylsilane–vinylsilane difunctionalization by silylcupration of allene followed by reaction with α,β-unsaturated nitriles

Silylcupration of allene using phenyldimethylsilylcopper 1 followed by BF3-mediated reaction with alpha,beta-unsaturated nitriles at -40 degrees C affords allylsilane-vinylsilane-containing ketones resulting from consecutive addition (1,2 and 1,4) of the intermediate allyl- and vinylcopper species formed in the silylcupration of allene.

Reductive Cupration of Cyanoketene Dithioacetals. Generation of Functionalized (E)-Vinylcopper Reagents and Their Reactions with Electrophiles

Abstract Functionalized (E)-vinylcopper species, selectively generated by the effective reduction of cyanoketene dithioacetals with two equimolar amounts of cuprates, react with electrophiles such as water, allyl bromide, and acid chlorides to give the corresponding substitution products in good yields.

A Novel and Efficient Generation of Functionalized Vinylcopper Reagents and their Reactions with Electrophiles. Synthesis of β-Methylthiobutenolides

Abstract Ketene dithioacetals bearing an alkoxycarbonyl group at 2-position are effectively reduced by two equimolar amounts of dimethylcuprate derived from methyllithium and cuprous cyanide to yield the corresponding functionalized vinylcopper species. These organocopper species are efficiently trapped by carbon electrophiles. Formal substitution reactions of a methylthio group in ketene dithioacetals by electrophiles can be attained by one-pot operation. Synthesis of β-thiobutenolides was also achieved.