Selenosulfonation of 1,3-dienes: One-pot synthesis of 2-(phenylsulfonyl)-1,3-dienes

A one-pot procedure for the transformation of a 1,3-diene into the corresponding 2-(phenylsulfonyl)-1,3-diene was developed. The reaction involves a 1,2-selenosulfonation-oxidation sequence.     

Au-catalyzed synthesis of (1Z,3E)-2-pivaloxy-1,3-dienes from propargylic pivalates

Propargylic pivalates with electronically unbiased internal alkynes are selectively transformed into (1Z,3E)-2-pivaloxy-1,3-dienes containing various functionalities. The unusual selectivity of 1,2-acyloxy migration over the structurally preferred 3,3-rearrangement is realized. This reaction is highly stereoselective and offers rapid access to dienes for one-pot intra-/intermolecular Diels-Alder reactions either under thermal conditions or with Lewis acid catalysis.     

Stereoselective preparation of 1-chloro-(E,E)-1,3-dienes. Application to the synthesis of methyl eleostearate.

The nickel (or palladium) catalyzd reaction of alkenylalanes with (E)-di-chloroethylene affords 1-chloro-(E,E)-1,3-dienes under mild conditions. The syntheses of methyl -eleostearate which is reported to be a feeding deterrent for the boll weevil on cotton, and one of its isomers, methyl punicate, are described.     

Gamma-allyl phosphinoyl phenyl sulfone (GAPPS): a conjunctive reagent for the synthesis of EE, EZ, and ET 1,3-dienes

A three-operation conjunctive strategy is available for the synthesis of EE, EZ, and ET dienes. This protocol employs a sequential Wadsworth-Emmons reaction using a GAPPS reagent followed by alkylation of an allylic sulfone anion, and finally ligand-mediated, palladium-catalyzed desulfonylation.     

A highly stereoselective synthesis of (E)-1-substituted-1,3-dienes

(E)-1-substituted-1,3-dienes are obtained with high stereoselectivity by the thermal extrusion of SO₂ from 2-substituted-2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels-Alder reaction. An application to the synthesis of (E)-9,11-dodecadien- 1-yl acetate, a sex pheromone of the red-bollworm moth is described.     

A facile stereospecific synthesis of （Z）-2-sulfonyl-substituted 1,3-enynes via Sonogashira coupling of （E）-α-iodovinyl sulfones with 1-alkynes

(E)-a-Iodovinyl sulfones 1 underwent the Sonogashira coupling reactions with terminal alkynes 2 in piperidine at room temperature in the presence of 5 mol% of Pd(PPh3)4 and 10 mol% of CuI to stereospecifically afford the corresponding (Z)-2- sulfonyl-substituted 1,3-enynes 3 in high yields.     

Equilibrium control in enyne metathesis: crossover studies and the kinetic reactivity of (E,Z)-1,3-disubstituted-1,3-dienes

The stereoselectivity of diene bond formation in the ruthenium-carbene mediated intermolecular enyne metathesis was studied. Initial reaction between an alkyne and 1-hexene gave mixtures of E- and Z-isomers in the newly formed 1,3-diene. However, over time the mixtures equilibrated to form mostly the diene of the E-configuration. To evaluate individual reactivity of the E- and Z-dienes, they were independently synthesized. The E-diene was found to be kinetically-stable under nominal metathesis conditions while the Z-diene isomerized to the E-isomer. The Z-isomeric dienes were found to react with other alkenes to produce a new diene of E-configuration. A secondary metathesis mechanism involving ruthenium alkylidene intermediates was invoked to explain the dynamic stereochemistry observed in this study.     

Conformational Properties of (Z,Z)-, (E,Z)-, and (E,E)-Cycloocta-1,4-dienes

Summary.  Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and the MP2/6-31G^*//HF/6-31G^* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C ₂-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C _S-symmetric boat-boat geometry is 19.1 kJ·mol⁻¹. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C ₁) transition state which is 43.5 kJ·mol⁻¹ above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol⁻¹ more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol⁻¹, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol⁻¹. The C _S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C _S) transition state which is 37.2 kJ·mol⁻¹ above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol⁻¹ less stable than the crown conformation. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 3, 2002     

Reaction of (Z)-1-aryl-3-hexen-1,5-diynes with sodium azide: synthesis of 1-aryl-1H-benzotriazoles

[reaction: see text] A novel tandem cascade reaction involving 1,3-dipolar cycloaddition reaction, anionic cyclization, and sigmatropic rearrangement for the synthesis of 1-aryl-1H-benzotriazoles 2 and 3 was accomplished by treatment of the (Z)-1-aryl-3-henen-1,5-diynes (1) with sodium azide in DMF or DMSO at 80 degrees C for 12 h and gives 65-91% yields.     

Mild and selective palladium-catalyzed dimerization of terminal alkynes to form symmetrical (Z,Z)-1,4-dihalo-1,3-dienes

A regioselective and stereoselective palladium-catalyzed dimerization of terminal alkynes method for the synthesis of symmetrical (Z,Z)-1,4-dihalo-1,3-dienes is presented. In the presence of a catalytic amount of PdX(2) and 3 equiv of CuX(2) (X = Cl and Br), terminal alkynes were dimerized to afford (Z,Z)-1,4-dihalo-1,3-dienes in good yields. The results showed that the effect of solvent had a fundamental influence on the chemoselectivity of the dimerization reaction. The mechanism of the palladium-catalyzed dimerization reaction is also discussed.     

Probing the Lewis acid-catalyzed intramolecular Diels-Alder cyclizations of allylic alkoxy-substituted (Z)-1,3-dienes

[reaction: see text] The Lewis acid-promoted Diels-Alder reaction of (E,Z,E)-trienal 1 provides not only the expected cis-fused cycloadduct 16 but also the trans-fused products 17 and 18. Trans-fused cycloadducts 17 and 18 are also products of the Lewis acid-promoted cyclization of (E,Z,E)-trienyl acetal 2. These products presumably derive from a stepwise cyclization pathway.     

Flash vacuum pyrolysis of 1-methoxy-1,3-bis(trimethylsiloxy)-1,3-dienes: synthesis of α-allenic acids.

Flash vacuum pyrolysis at 680–700°C of 2- and 4- substituted 1-methoxy-1,3-bis (trimethylsiloxy)-1,3-butadienes yields α-allenic silyl esters which, upon hydrolysis, provide a direct route to α-allenic acids with good overall yield.     

(Z,Z)-2,3-bis(trimethylsilyl)-1,4-dibromo- and 2,3-bis(trimethylsilyl)-1,1,4,4-tetrabromobuta-1,3-dienes. Synthesis and Diels-Alder reactions.

The two title compounds (1,2) have been prepared and some Diels-Alder reactions investigated.     

Electron-deficient 1- and 2-azabuta-1,3-dienes: a comprehensive survey of their synthesis and reactivity

Electron-deficient 1- and 2-azabuta-1,3-dienes are reagents intrinsically able to provide a wide range of cyclic and acyclic N-containing building blocks. Depending on their substitution, they behave as dienes for Diels-Alder reactions, as partners for [4+1], [3+2], [2+2]-cycloadditions, for aziridinations and as electrophiles for 1,2 and 1,4-additions. Nowadays, they are a very versatile family of compounds, despite their usual instability and complex reactivity. Four decades of research in this challenging area are reviewed in this critical review: their synthetic aspects and their reactivity towards a wide range of dienophiles, dipoles and nucleophiles are described as well. The introduction focuses on their electronic properties in order to get a clear picture of their reactivity (190 references).