Gold(I)-catalyzed propargyl Claisen rearrangement

Homoallenic alcohols are prepared from propargyl vinyl ethers using a trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, as a catalyst for propargyl Claisen rearrangement at room temperature. The gold(I)-catalyzed reaction is effective for a diverse collection of propargyl vinyl ethers, including substrates containing aryl and alkyl groups at the propargylic position, and hydrogen, aryl, and alkyl substituents at the alkyne terminus. Tertiary propargyl vinyl ethers can be employed in the reaction, at slightly elevated temperatures, to afford tetrasubstituted allenes. Importantly, the rearrangement of 1,2-disubstituted vinyl ethers proceeds with excellent diastereoselectivity, and the rearrangement of chiral nonracemic propargyl vinyl ethers proceeds with excellent chirality transfer to furnish enantioenriched allenes.     

Microwave-assisted domino access to C2-chain functionalized furans from tertiary propargyl vinyl ethers

Tertiary propargyl vinyl ethers armed with an electron-withdrawing group (amide or ester) at the tertiary propargylic position have been efficiently transformed into trisubstituted C(2)-chain functionalized furans. The metal-free domino transformation involves a microwave-assisted tandem [3,3]-propargyl Claisen rearrangement/5-exo-dig O-cyclization reaction. The manifold can be performed in a one-pot fashion from the primary components (1,2-ketoester/1,2-ketoamide or tertiary propargyl alcohols).     

One-pot synthesis of 1,2-dihydropyridines: expanding the diverse reactivity of propargyl vinyl ethers

The catalyzed synthesis of 1,2-dihydropyridines starting from easily accessible propargyl vinyl ethers was realized. The reaction sequence involving a transition metal-catalyzed propargyl-Claisen rearrangement, a condensation step, and a Br?nsted acid-catalyzed heterocyclization furnishes the highly substituted heterocycles in moderate to excellent yields. Additionally, a practical one-pot protocol toward 1,2-dihydropyridines and 2H-pyrans starting from propargylic alcohols was developed.     

Reductive deprotection of propargyl ether by a SmI2-amine-water system and its application to polymer-supported oligosaccharide synthesis

A SmI₂-amine-water system instantaneously deprotected aryl and alkyl propargyl ethers in a reductive manner. The utility of the propargyl group as a protecting group in oligosaccharide synthesis, and its application to polymer-supported oligosaccharide synthesis is described.     

Addition of a 3-alkoxy allenylzinc to N-acyliminium ions: new entry to propargyl syn-1,2-aminoalcohol units

A new addition reaction of a 3-alkoxy allenylzinc reagent to N-acyliminiums prepared in situ from imines and acid halides is reported. Unlike addition onto imines or nitrones that affords the trans adducts, acetylenic syn-1,2 amino ethers are yielded with good selectivities, thus providing a new entry to propargyl syn-1,2-aminoalcohol units.     

Spectroscopic investigation of propargyl aryl ethers

Conclusions The UV, Raman, and IR spectra of propargyl ethers are evidence of the absence of interaction between the CC group and the oxygen atom through the methylene bridge.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 84–87, January, 1974.     

Regio- and stereoselective homolytic hydrostannylation of propargyl alcohols and ethers with dibutylchlorostannane

The Et3B-initiated reaction of gamma-unsubstituted propargyl alcohols with dibutylchlorostannane (Bu2SnClH) at low temperature gave (Z)-vinylstannanes with high regio- and stereoselectivity. The corresponding alkyl propargyl ethers also underwent regio- and stereoselective homolytic hydrostannylation with Bu2SnClH; however, the regioselectivity was not so high as that with the propargyl alcohols.     

Synthesis of propargyl ethers,possessing bactericidal properties

Conclusions Some derivatives of the propargyl ethers of phenols, possessing bactericidal properties, were synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimieheskaya, No. 11, pp. 2591–2593, November, 1968.     

Synthesis of Fréchet type dendritic benzyl propargyl ether and Fréchet type triazole dendrimer

Fréchet type dendritic benzyl propargyl ethers were synthesized by the reaction of propargyl bromide with the corresponding Fréchet type dendritic benzyl alcohol. A propargyl focal point functionalized dendrons were applied for the construction of symmetric and unsymmetric dendrimers containing 1,2,3-triazole rings as connectors via click chemistry with a tripodal azide core or a azide focal point functionalized Fréchet type dendrons.     

Enhanced diastereoselectivity in beta-mannopyranosylation through the use of sterically minimal propargyl ether protecting groups

[reaction: see text] 2-O-Propargyl ethers are shown to be advantageous in the 4,6-O-benzylidene acetal directed beta-mannosylation reaction. The effect is most pronounced when the O3 protecting group is a bulky silyl ether or a glycosidic bond; however, even with a 3-O-benzyl ether, the use of a 2-O-propargyl ether results in a significant increase in diastereoselectivity. The beneficial effect of the propargyl ether is thought to be a combination of its minimal steric bulk, as determined by a measurement of the steric A-value and of its moderately disarming nature, as reflected in the pKa of propargyl alcohol. Conversely, the application of a 3-O-propargyl ether in the benzylidene acetal directed mannosylation has a detrimental effect on stereoselectivity, for which no explanation is at present available. Deprotection is achieved by base-catalyzed isomerization of the propargyl ether group to the corresponding allenyl ether, followed by oxidative cleavage with N-methylmorpholine N-oxide and catalytic osmium tetroxide.     

Cobalt-catalyzed cycloisomerization of 1,6-enynes and allyl propargyl ethers

[reaction: see text] 1,6-Enynes and allyl propargyl ethers undergo a cobalt-catalyzed formal 5-endo-dig cyclization to form vinyl cyclopentenes and dihydrofurans, respectively. The use of equimolar amounts of dicobalt octacarbonyl and trimethyl phosphite affords optimum yields and improved selectivity for cycloisomerization vs alkene isomerization.     

Haloheterocyclization of 2-methallyl(propargyl)-thioquinoline-3-carbaldehydes

Interaction of 2-methallyl(propargyl)thioquinoline-3-carbaldehydes with halogens leads to the formation of 4-formyl-1-halomethyl(halomethylidene)-1,2-dihydrothiazolo[3,2-a]quinolinium halides.     

Novel carbon-carbon bond-forming reactions using carbocations produced from substituted propargyl silyl ethers by the action of TMSOTf.

Highly useful carbon-carbon bond forming reactions using stable allenyl, propargyl, or allyl-propargyl hybrid cations have been developed. These carbocations could be generated from silyl 1-(pi-donor)-substituted propargyl ethers by the action of trimethylsilyl trifluoromethanesulfonate in dichloromethane at -78 degrees C to room temperature and could be attacked nucleophilically by electron rich arenes, allylsilanes, or enol silyl ethers, giving rise to allenes, alkynes, and their derivatives. A novel method for regio- and stereoselective synthesis of conjugated enynes utilizing allyl-propargyl hybrid cations has also been established.     

Selective cleavage of allyl and propargyl ethers to alcohols catalyzed by Ti(O-i-Pr)4/MXn/Mg

[reaction: see text] Allyl and propargyl ethers were effectively deallylated or depropargylated to the parent alcohols via a C-O bond cleavage catalyzed by a low-valent titanium reagent (LVT), Ti(O-i-Pr)4/TMSCl/Mg or Ti(O-i-Pr)4/MgBr2/Mg, under mild reaction conditions. Differentiation between the allyl and propargyl ethers was achieved by the reaction in the presence of AcOEt as an additive. The reagent also catalyzed intra- and intermolecular cyclotrimerization reactions of alkynes to substituted benzenes.     

Facile synthesis of unusual glycosyl carbamates and amino acid glycosides from propargyl 1,2-orthoesters as glycosyl donors

Propargyl 1,2-O-orthoesters are exploited for the synthesis of 1,2-trans O-glycosides of protected amino acids. N-Fmoc- and N-Cbz protected serine/threonine - benzyl/methyl esters reacted well with glucosyl-, galactosyl-, mannosyl- and lactosyl- derived propargyl 1,2-orthoesters affording respective 1,2-trans glycosides in good yields under AuBr(3)/4 ? MS Powder/CH(2)Cl(2)/rt. t-Boc serine derivative gave serine 1,2-orthoester and glycosyl carbamate. Optimized conditions enabled preparation of new glycosyl carbamates from N-Boc protected amines in a single step using gold catalysts and propargyl 1,2-orthoesters in excellent yields.     

Synthesis of 1,2-Bis[propargyl(or allyl)oxy]cycloalkanes

Reactions of cyclic olefins with propargyl and allyl alcohols in the presence of crystalline iodine and a catalytic amount of Ag₃PW₁₂O₄₀ afforded in one step trans-1,2-bis[propargyl(allyl)oxy]cycloalkanes.     

Synthesis of propargyl C-glycosides using allenyltributylstannane

Protected propargyl C-glycosides have been prepared by activation of the anomeric centres of 2,3,4,6-tetra-O-benzyl- derivatives of d-glucose and d-galactose, followed by treatment with allenyltributylstannane in the presence of Lewis-acid. Activation was by formation of the anomeric acetates, trichloroacetimidates or fluorides; boron trifluoride etherate and trimethylsilyl trifluoromethanesulfonate were particularly effective Lewis-acids. Attempts to perform similar reactions on 1,2,3,4,6-penta-O-acetyl-d-glucose led to participation by the C-2 acetate group and formation of 3,4,6-tri-O-acetyl-1,2-O-[1-(prop-2-ynyl)ethylidene]-α-d-glucopyranose.     

Ruthenium-catalyzed functionalization of pyrroles and indoles with propargyl alcohols

Several ruthenium-catalyzed atom-economic transformations of propargyl alcohols with pyrroles or indoles leading to alkylated, propargylated, or annulated heteroaromatics are reported. The mechanistically distinct reactions are catalyzed by a single ruthenium(0) complex containing a redox-coupled dienone ligand. The mode of activation regarding the propargyl alcohols determines the reaction pathway and depends on the alcohols' substitution pattern. Secondary substrates form alkenyl complexes by a 1,2-hydrogen shift, whereas the transformation of tertiary substrates involves allenylidene intermediates. 1-Vinyl propargyl alcohols are converted by a cascade allylation/cyclization sequence. The environmentally benign processes are of broad scope and allow the selective synthesis of highly functionalized pyrroles and indoles generating water as the only waste product.     

Haloheterocyclization of 2-allyl(propargyl)oxyquinoline-3-carbaldehydes

The reaction of 2-allyl(propargyl)oxyquinoline-3-carbaldehydes with halogens gives 1-bromomethyl(bromomethylidene)-4-formyl-1,2-dihydrooxazolo[3,2-a]quinolinium halides. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1204–1207, August, 2007.     

The role of cesium fluoride in aryl propargyl ether Claisen rearrangement and its mechanistic elucidation: a theoretical study

The role of cesium fluoride (CsF) in aryl propargyl ether Claisen rearrangement and its mechanistic pathway have been investigated in gas and solvent phase using the density functional theory implemented in Gaussian 09. Our results indicate that the [3,3]-sigmatropic rearrangement is the rate-limiting step with ΔG ^? value of 37.1 kcal/mol in solvent phase. Furthermore, the results show that the enolization of α-allenylketone intermediate (Int1-CsF) has a higher free energy barrier, which implies that the formation of benzopyran is not favored in the presence of CsF. However, the abstraction of the α-hydrogen atom in Int1-CsF with CsF shows a very low free energy barrier and is the most favored pathway for aryl propargyl ether Claisen rearrangement in the presence of CsF to form benzofuran. In the case of substituted aryl propargyl ethers, a methoxy group on the benzene ring lowers the activation barrier. The HOMO–LUMO, conformational and NBO analysis indicate that increasing methyl substitution on the propargyl residue enhances the rearrangement reaction.