Suzuki-Miyaura cross-coupling of alkenyl tosylates with alkenyl MIDA boronates

A practical procedure for the palladium-catalysed Suzuki-Miyaura coupling of various alkenyl tosylates with alkenyl MIDA boronates has been developed. Commercially available trans-bromo[N-succinimidyl-bis(triphenylphosphine)]palladium(II) [Pd(PPh₃)₂NBS] is an effective catalyst under the slow release conditions of MIDA boronates; with less activated alkenyl tosylates addition of the cheap, air-stable tricyclohexylphosphine tetrafluoroborate enhances reactivity.     

Sulfotrioxidation of perfluoroisopropyl alkenyl ethers

Conclusions The reactions of perfluoroisopropyl allyl I and perfluoroisopropyl propenyl ethers with SO₃ have been examined. In the presence of B₂O₃, (I) forms perfluoro--isopropoxyallyl fluorosulfate, which is an alkylating agent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimcheskaya, No. 12, pp. 2796–2798, December, 1982.     

Anionic cross-coupling reaction of alpha-metallated alkenyl sulfoximines and alkenyl sulfoximines with cuprates featuring a 1,2-metal-ate rearrangement of sulfoximine-substituted higher order alkenyl cuprates and an alpha-metallation of alkenyl sulfoximines by cuprates

(E)- and (Z)-configured alpha-lithioalkenyl sulfoximines, which are available through lithiation of the corresponding alkenyl sulfoximines, undergo a anionic cross-coupling reaction (ACCR) with organocuprates with formation of the corresponding alkenyl cuprates and sulfinamide. The alkenyl cuprates can be trapped by electrophiles. The ACCR presumably proceeds via the formation of a higher-order sulfoximine-substituted alkenyl cuprate, which undergoes a 1,2-metal-ate rearrangement whereby the sulfoximine group acts as the nucleofuge. The parent (E)- and (Z)-configured alkenyl sulfoximines suffer upon treatment with an organocuprate a deprotonation at the alpha-position with formation of the corresponding alpha-cuprioalkenyl sulfoximines. These derivatives also enter into a similar ACCR with organocuprates. The ACCR of sulfoximines substituted homoallylic alcohols allows a stereoselective access to enantio- and diastereopure substituted homoallylic alcohols.     

Novel applications of alkenyl zirconocenes

Alkenyl zirconocene complexes are readily obtained by diverse processes including hydrozirconation, carbozirconation, and cyclozirconation of alkynes, transmetalations, and bond insertions. In combination with other metals, novel reaction manifolds can emerge and provide access to useful synthetic building blocks. Both catalytic asymmetric processes and highly diastereoselective multicomponent transformations that involve the formation of three or more new carbon-carbon bonds are feasible. This Concept paper summarizes the current state of the art and opportunities for future reaction discovery in this field of research, with particular emphasis on synergistic effects of bimetallic combinations of zirconocenes and zinc.     

Direct carbamoylation of alkenyl halides

Alkenyl chlorides and bromides are converted into tertiary enamides by treatment with a carbamoylsilane in toluene at 110 degrees C in the presence of phosphine-palladium(0) catalysts. [reaction: see text]     

Copper-catalyzed hydroboration of alkenyl oxindoles

Herein we describe the NHC-Cu(I)-catalyzed hydroboration of alkenyl oxindoles. The corresponding boronates were obtained in good yields, under operationally simple and environmentally friendly conditions, using ethanol as the solvent. Our studies revealed that water-based systems were not very effective. Furthermore, the obtained products are amenable to further elaboration and can be useful to the synthesis of a broader range of oxindole-containing molecules with biological relevance.     

Iron-catalyzed alkylation of alkenyl Grignard reagents

The first iron-catalyzed cross-coupling reaction between alkenyl Grignard reagents and n- or s-alkyl bromides is described. The reaction is stereoselective and takes place in the presence of 5 mol % of [Fe(acac)3/TMEDA/HMTA] (1:2:1) under very mild conditions (THF, 0 degrees C, 45 min).     

Mass spectra of alkenyl methyl ethers

Electron impact ionization mass spectra of numerous alkenyl methyl ethers C_nH_2n-1OCH₃ (n = 3–6) recorded under normal (4 kV, 70 eV, 175°C) and low-energy, low-temperature (8 kV, 12 eV, 75 °C) conditions are reported. The influence of the position and stereochemistry of the double bond on the dissociation of ionized alkenyl methyl ethers is discussed. The mechanisms by which these ethers fragment after ionization have been further investigated using extensive ²H-labelling experiments and by studying the energy dependence of the reactions. Ethers of allylic alcohols show spectra that are distinct from those of the isomeric species in which the double bond is separated by one or more sp³ carbon atoms from the carbon atom carrying the methoxy group. Three principal primary fragmentations are observed. The most common process, especially for ionized ethers of allylic alcohols, is loss of an alkyl group. This reaction often occurs by simple α-cleavage of radical-cations of the appropriate structure; however, alkyl groups attached to either end of the double bond are also readily lost. These formal β- and γ-cleavages are explained in terms of rearrangements via distonic ions and, at least in the case of γ-cleavages, ionized methoxycyclopropanes. Ionized homoallyl methyl ethers tend to eliminate an allylic radical, particularly at high internal energies, with formation of an oxonium ion (CH₃ ⁺O?CH₂ or CH₃ ⁺O?CHCH₃). The ethers of linear pentenols and hexenols show abundant [M - CH₃OH]⁺? ions in their spectra, especially when a terminal methoxy group is present Methanol loss also takes place from ionized ethers of allylic alcohols in which there is a Δ-hydrogen atom; this process is significantly favoured by cis, rather than trans, stereochemistry of the double bond.     

The facile preparation of alkenyl metathesis synthons

We report synthetic methodology allowing the preparation of any length alkenyl halide from inexpensive starting reagents. Standard organic transformations were used to prepare straight chain α-olefin halides in excellent overall yields with no detectable olefin isomerization and full recovery of any unreacted starting material. Reported transformations can be used for the selective incorporation of pure α-olefin metathesis sites in highly functionalized molecules.     

Palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles

Reaction of 1-methyl-2-(4-pentenyl)indole with a catalytic amount of PdCl2(CH3CN)2 (5 mol %) and a stoichiometric amount of CuCl2 (3 equiv) in methanol under CO (1 atm) at room temperature for 30 min led to cyclization/carboalkoxylation to form the corresponding tetrahydrocarbazole in 83% isolated yield as a single regioisomer. Palladium-catalyzed cyclization/carboalkoxylation of 2-(4-pentenyl)indoles tolerated substitution along the alkenyl chain and at the internal and cis-terminal olefinic positions. Palladium-catalyzed cyclization/carboalkoxylation tolerated a range of alcohols and was effective for the cyclization of 2-(3-butenyl)indoles, 3-(3-butenyl)indoles, 3-(4-pentenyl)indoles, and 2-(5-hexenyl)indoles.     

Synthesis of alkenyl 3-hydroxy-2-naphthoates

Esterification of 3-hydroxy-2-naphthoic acid with homologous primary and secondary alkenyl alcohols with different chain lengths in the presence of N,N'-carbonyldiimidazole (CDI) and 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide gave the corresponding esters.     

Intramolecular palladium-catalyzed direct arylation of alkenyl triflates

A catalyst generated from Pd(OAc)2 and dppp is effective for the direct intramolecular arylation of alkenyl triflates. Conjugated alkene-arene-containing carbocycles are produced in good yield. The process tolerates a variety of aryl substituents as well a simple heteroaryl groups. Electron-deficient aryl rings deliver faster reactions.     

Indium-catalyzed homo-Nazarov cyclizations of alkenyl cyclopropyl ketones

Herein, an efficient Lewis acid catalyzed protocol for the homo-Nazarov cyclizations of alkenyl cyclopropyl ketones is reported. Alkenes bearing β-hydrogens (or silyl groups) provide 1.5:1 mixtures of methylene cyclohexenols and cyclohexenones. When no β-hydrogens (or silyl groups) are present, only cyclohexenones are observed. Products are rapidly formed in good to high yields (up to 93%) under mild conditions and could be readily derivatized.     

Sigmatropic rearrangements of alkenyl benzofuryl and benzothienyl sulfides

The thio Claisen rearrangement of 2-butenyl 2-benzofuryl sulfide, cyclopenten-2-yl 2-benzofuryl sulfide, 2-butenyl 2-benzothienyl sulfide, and cyclopenten-2-yl 2-benzothienyl sulfide was investigated. The rates, energies and entropies of activation of the process were calculated, and the effect of the structure of the sulfide, the polarity of the solvent, and the temperature was demonstrated by comparison of these values. The 1,3-thioallyl rearrangement of 1-methylallyl 3-methyl-2-benzothienyl sulfide was studied, and it was shown that this reaction competes with the thio Claisen rearrangement.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1338–1341, October, 1982.     

A force-field study of alkenyl radical ring closure

In accord with stereoelectronic considerations there is a good correlation between the relative rates, regiochemistry, and stereochemistry of ring closure of ω-alkenyl radicals, and the strain energies of transition structures determined by force field calculations.     

Palladium-catalyzed direct functionalization of benzoxazoles with alkenyl iodides

A straightforward procedure for the palladium-catalyzed direct functionalization of benzoxazoles with alkenyl iodides is described. The reactions employ a Pd(II)-precatalyst and use ‘on water’ conditions to achieve the ready union of a range of di- and tri-substituted alkenyl iodides with a small range of benzoxazoles.     

Ruthenium-catalyzed reaction of alkenyl triflates with zinc thiolates

A ruthenium complex coordinated with 3,4,7,8-tetramethyl-1,10-phenanthroline catalyzed the reaction of alkenyl triflates with zinc dithiolates to give alkenyl sulfides.