Palladium-catalyzed alkylation of vinyl oxiranes with substituted allenes. Direct access to bifunctionalized allylic alcohols

The first palladium-catalyzed alkylation of vinyl oxiranes with substituted allenes to form functionalized allylic alcohols is described. The reaction of activated allenes 5 with vinyl oxiranes 1 in the presence of catalytic amounts of Pd(PPh(3))(4) (10 mol %) and 1,3-bis(diphenylphosphino)propane (dppp) (20 mol %) in THF at 60 degrees C gave the corresponding allylic alcohols 6 in good to excellent yields. The allylic alcohols were obtained in different ratios of trans/ cis isomers.     

Nucleophilic epoxidation of alpha'-hydroxy vinyl sulfoxides

The nucleophilic epoxidation of a variety of alpha'-(1-hydroxyalkyl) vinyl sulfones and sulfoxides has been studied. The sulfones give rise to anti oxiranes with modest (E) or excellent (Z) selectivities and in good yields. The (E)-sulfoxides display low reactivity within a reinforcing/nonreinforcing scenario. The use of t-BuOOLi in Et(2)O allows for a highly syn-selective epoxidation-oxidation. The (Z)-sulfoxides display a remarkably high reactivity under these conditions. The reinforcing (S,S(S)) diastereomers (3e-g) yield hydroxy sulfinyl oxiranes with high yields and selectivities. In contrast, the (R,S(S)) diastereomers (4e-g) show diminished reactivities and a very substrate-dependent stereochemical outcome. The structure of these oxiranes has been secured by chemical correlations and an X-ray crystal structure.     

Remarkable selectivity in addition of alcohols to epoxydienes of 5,7 bicyclic and 5,7,6 tricyclic systems

Acid-catalyzed addition of alcohols to tricyclic dienyl epoxides such as 4 or bicyclic vinyl oxiranes such as 17 exclusively occurred at the vinyl terminus of unsaturated system through a typical S(N)2' process affording 1,6- and 1,4-dioxygenated derivatives, respectively.     

Stereoselective 1,4-addition of dialkylaluminum benzenethiolate to vinyl oxiranes

Reactions of vinyl oxiranes and diethylaluminum benzenethiolate in benzene at room temperature proceed regio- and stereoselectively to afford mainly ($\text{Z}$)-4-phenylthio-2-buten-1-ol derivatives in good yields.     

Novel supramolecular catalysis in the controlled synthesis of polymers and block copolymers

Novel carbanionic polymerization of vinyl monomers as styrene, methyl methacrylate, as well as ring opening polymerization of oxiranes and lactones mediated by supramolecular complexes of alkali metals is demonstrated.     

An efficient construction of bicyclic systems containing a seven-membered ring by tandem ring-closing metathesis reactions of dienynes

Various (5–7) and (6–7) bicyclic dienes bearing quaternary methyl group and ester functionality have been synthesized from acyclic dienynes by tandem ring-closing metathesis (RCM) reaction. Epoxidation of these conjugated dienes led to bicyclic vinyl oxiranes which undergo acid-catalyzed addition of alcohols to afford highly oxygenated compounds.     

Triaryl(1-pyrenyl)bismuthonium salts: efficient photoinitiators for cationic polymerization of oxiranes and a vinyl ether

Photoirradiation of triaryl(1-pyrenyl)bismuthonium salts in acetonitrile afforded triarylbismuthanes and pyrene, accompanied by the generation of protic acids. Triaryl(1-pyrenyl)bismuthonium hexafluoroantimonates have proven to behave as efficient photoinitiators for cationic polymerization of oxiranes and a vinyl ether, affording the corresponding polymers in good yields within 1 min.     

First enantioselective synthesis of vinyl oxiranes from aldehydes and ylides generated from allyl halides and chiral sulfides

Asymmetric allylidenation of aldehydes with sulfur ylides is possible with proper substitution of the initial sulfide, to avoid the [2,3] sigmatropic rearrangement of the unsaturated ylides. One-pot reaction of (2R,5R)-dimethylthiolane with allyl halides, aldehydes, and sodium hydroxide in tert-butyl alcohol affords vinyl oxiranes in good yields. Enantiomeric excesses up to 90% and trans selectivities have been achieved with methallyl-type halides.     

A facile method for the synthesis of 1,3-oxathiolan-2-ones by reaction of oxiranes, sulfur, and carbon monoxide

A new method for the synthesis of 1,3-oxathiolan-2-ones has been developed. When oxiranes were allowed to react with sulfur in the presence of a catalytic amount of sodium hydride under pressurized carbon monoxide, the three-component coupling of oxiranes, sulfur, and carbon monoxide smoothly proceeded to give the 1,3-oxathiolan-2-ones in moderate to good yields. The reaction proceeded with a high regioselectivity and stereospecificity. For the reaction of oxiranes possessing an aromatic ring, the yields of the 1,3-oxathiolan-2-ones were lower than that of the oxiranes possessing no aromatic ring due to the formation of alkenes and thiiranes as byproducts. However, the product yields were improved by the addition of a catalytic amount of selenium.     

A stereodivergent synthesis of beta-hydroxy-alpha-methylene lactones via vinyl epoxides

A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalized building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards beta-hydroxy-alpha-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into trans beta-hydroxy-alpha-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO2 insertion and cyclisation sequence gave the cis beta-hydroxy-alpha-methylene lactone counterparts along with an interesting cis-trans equilibration of the pi-allyl intermediates.     

Efficient Regioselective Ring Opening of Oxiranes with Thioacids in the Presence of β‐Cyclodextrin in Water

A mild and convenient synthesis of β‐hydroxy thioesters has been achieved by the regioselective ring opening of oxiranes using thioacetic acid and thiobenzoic acid in the presence of β‐cyclodextrin in water at room temperature. β‐Hydroxy thioesters are realized in high yields, and β‐cyclodextrin can also be recovered and reused.     

Copper Salt Catalyzed Synthesis of Functionalized 2H‐Pyranes

A copper‐catalyzed reaction between terminal alkynes, oxiranes, and malonitrile has been described. In this transformation, copper acetylide was attacked on oxiranes to form homopropargyl alkoxy‐copper intermediate that was further transferred to 2H‐pyrane skeletons by reaction with malonitrile. We found that the reaction was not productive without hexafluoroisopropanol.     

Pd/C‐Catalyzed Carbonylative Esterification of Aryl Halides with Alcohols by Using Oxiranes as CO Sources

A carbonylative esterification reaction between aryl bromides and alcohols, promoted by Pd/C and NaF in the presence of oxiranes, has been developed. In this process, oxiranes serve as sources of carbon monoxide by their conversion to aldehydes through a palladium‐promoted Meinwald rearrangement pathway. Intramolecular versions of this process serve as methods for the synthesis of lactones and phthalimides.     

Benzophenone based addition fragmentation agent for photoinitiated cationic polymerization

Photoactive allyl ammonium salt (BPEA) containing benzophenone moiety in the structure was synthesized and characterized. Its capability to act as a self-initiating addition fragmentation agent in the photoinitiated cationic polymerization of oxiranes such as cyclohexene oxide and vinyl monomers such as butylvinyl ether was investigated. These monomers turned out to be polymerizable in the presence of BPEA provided free radicals are generated photochemically at λ>300 nm by hydrogen abstraction of excited benzophenone moiety. Accordingly, a free radical adds to the carbon-carbon double bond of a ground state BPEA and fragmentation of the adduct radical results in the formation of reactive ammonium radical cation which is essentially responsible for the initiation.     

From an Epoxide Monomer Toolkit to Functional PEG Copolymers With Adjustable LCST Behavior

The lower critical solution temperature (LCST) behavior of novel poly(ethylene glycol) (PEG)‐based copolymers bearing multiple functional groups, obtained by anionic ring‐opening (co)polymerization (AROP), has been investigated. Variable comonomer ratios of ethylene oxide (EO) and the corresponding oxiranes isopropylidene glyceryl glycidyl ether (IGG), ethoxyl vinyl glycidyl ether (EVGE), allyl glycidyl ether (AGE), or N,N‐dibenzyl amino glycidyl (DBAG), particularly designed to implement functional groups at the PEG backbone, were found to influence the LCST behavior. Sharp transitions from translucent to opaque solutions, comparable to other well‐established stimuli‐responsive polymers, were observed at temperatures ranging from 9 to 82 °C. The influence of the side group hydrophobicity could be quantified by the comparison of the different copolymer systems observed.     

Substituent effect on the 1H NMR Spectra of trans aryl methyl oxiranes and arylpropenes

The ¹H NMR spectra of 1-aryl-2-methyl oxiranes substituted in the phenyl ring and of the corresponding vinyl derivatives have been analysed. The substituent effect on oxiran protons seems mostly polar in character, as shown by correlations with substituent constants, solvent effects and the fact that perturbation decreases with increasing distance from the substituent. The comparison with the corresponding vinyl derivatives, in which conjugation effects are present, confirms this point. The results also seem to exclude the possibility of substituents causing significant changes on the preferred conformation of the phenyl ring. Ring current contributions on oxirane protons, evaluated by SCF procedure, show that their change with substituents is very small and does not represent a significant part of the change of proton chemical shift with substituents.     

Ethynyloxirane anions: a new tool for natural product synthesis

Ethynyl oxiranes can be deprotonated with nBuLi in THF and trapped with various electrophiles, providing a stereoselective access to trisubstituted oxiranes. Alkyl iodides and aldehydes react readily with the ethynyloxiranyl anions but not sulfonyl derivatives. Mechanistic investigations highlighted the stabilizing role of the ethynyl group, the localization of the anion and the coordinating role of the oxirane oxygen atom during deprotonation.     

Synthesis of β-hydroxy selenides using benzeneselenol and oxiranes under supramolecular catalysis in the presence of β-cyclodextrin in water

A simple and efficient method for the synthesis of β-hydroxy selenides is reported at room temperature in impressive yields for the first time by the highly the regioselective ring-opening of oxiranes with benzeneselenol in water under supramolecular catalysis in the presence of β-cyclodextrin. This is a direct one-pot synthesis of β-hydroxy selenides under mild conditions using water as solvent and has many advantages over the existing methodologies. β-Cyclodextrin can also be recovered and reused.     

Stepwise conversion of oxiranes to allylic alcohols by iodotrimethylsilane and DBU

Iodotrimethylsilane, prepared from hexamethyldisilane and iodine reacts smoothly with oxiranes to give (2-iodoalkoxy)trimethylsilanes which can be converted to allylic alcohols with DBU in good yields. The whole conversion can be carried out in one-pot operation.     

Reactions of 3-azido-1,2,4-triazole with electrophiles

Alkylation of 3-azido-1,2,4-triazole with oxiranes, bromoacetone, and methyl vinyl ketone furnished a mixture of N-substituted 3- and 5-azido-1,2,4-triazoles, 3-azido compounds prevailing. The same substrate subjected to heterylation with 3,5-dinitro-1,2,4-triazole derivatives reacted selectively at the N¹ atom, and its bromination afforded 3-azido-5-bromo-1,2,4-triazole..Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11, 2004, pp. 1699–1704.Original Russian Text Copyright © 2004 by Kofman, Krasnov.