Kinetic and Dynamic Kinetic Resolution of Racemic Tertiary Bromides by Pentanidium-Catalyzed Phase-Transfer Azidation

We have developed a method to afford enantiomerically enriched tertiary azides and bromides through pentanidium-catalyzed kinetic resolution (KR) of racemic tertiary bromides under base-free conditions. We found that the absence of water is crucial to attain a high selectivity factor (s). On the other hand, new experimental observations and DFT modeling led us to propose that enantioconvergent azidation of tertiary bromides proceeded through dynamic kinetic resolution (DKR). The investigations particularly identified the crucial roles of base and water in the enantioconvergent process, thus supporting the proposal that the tertiary bromide isomerizes in the presence of base and water through a S_N2X pathway.     

Kinetic and Dynamic Kinetic Resolution of Racemic Tertiary Bromides by Pentanidium‐Catalyzed Phase‐Transfer Azidation

We have developed a method to afford enantiomerically enriched tertiary azides and bromides through pentanidium‐catalyzed kinetic resolution (KR) of racemic tertiary bromides under base‐free conditions. We found that the absence of water is crucial to attain a high selectivity factor (s). On the other hand, new experimental observations and DFT modeling led us to propose that enantioconvergent azidation of tertiary bromides proceeded through dynamic kinetic resolution (DKR). The investigations particularly identified the crucial roles of base and water in the enantioconvergent process, thus supporting the proposal that the tertiary bromide isomerizes in the presence of base and water through a S_N2X pathway.     

Umlagerung intermediaerer 1,4-diradikale bei der photosensibilisierten addition von maleinsaeureanhydrid an propargylhalogenide

Photosensitized addition of maleic anhydride to propargyl bromides and tertiary propargyl chlorides gives rise to formation of vinylcyclopropane derivatives. Results are discussed in terms of a mechanism involving rearrangement of intermediate 1,4-alkyl-vinyldiradicals.     

Oxidative Addition to Palladium(0) Made Easy through Photoexcited‐State Metal Catalysis: Experiment and Computation

Visible‐light induced, palladium catalyzed alkylations of α,β‐unsaturated acids with unactivated alkyl bromides are described. A variety of primary, secondary, and tertiary alkyl bromides are activated by the photoexcited palladium metal catalyst to provide a series of olefins at room temperature under mild reaction conditions. Mechanistic investigations and density functional theory (DFT) studies suggest that a photoinduced inner‐sphere mechanism is operative in which a barrierless, single‐electron transfer oxidative addition of the alkyl halide to Pd⁰ is key for the efficient transformation.     

Oxidative addition reactions of group III metals in low oxidation states. Reactions of Ga2Br4 with alkyl bromides

The oxidative addition reactions of gallium “dibromide” with several primary, secondary and tertiary alkyl bromides, and bromides of the type (CH₂)_nBr₂ have been examined. Whilst all the organic halides readily react with Ga₂Br₄, only in two reactions, namely with methyl and ethyl bromides are isolatable compounds produced and in these cases oxidative addition may be represented as: Ga₂Br₄+RBr→RGa₂Br₅.     

An efficient method for the preparation of tertiary esters by palladium-catalyzed alkoxycarbonylation of aryl bromides

The palladium-catalyzed alkoxycarbonylation of aryl bromides is described for the efficient preparation of tertiary esters. The protocol proved compatible with a wide variety of functionalized (hetero)aromatic bromides, as well as several different sterically hindered tertiary alcohols, affording the alkoxycarbonylated products in high yields. Finally, the formation of aromatic trityl esters is discussed.     

Addition of tert-perfluoroalkyl bromides at a multiple bond,initiated by electron transfer

The thermodynamics of the dissociation of the radical-anions of perfluoroalkyl halides was determined by quantum-chemical methods. The conditions for the addition of tertiary perfluoroalkyl bromides to alkenes, initiated by electron transfer, were obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2308–2312, October, 1989.     

Interaction between Divalent Copper Fluoride and Carboxamide Group Enabling Stereoretentive Fluorination of Tertiary Alkyl Halides

Herein, we report a copper-catalyzed stereospecific fluorination involving CsF and α-bromocarboxamides as tertiary alkyl sources that, unlike traditional stereospecific routes involving stereoinversive S_N2 reactions, proceeds with retention of stereochemistry. The developed stereospecific Cu-catalyzed reaction is among the most efficient methods for synthesizing fluorinated molecules that possess highly congested stereogenic carbon centers. Mechanistic studies revealed that the combined reactivity of CuF₂ and Cs salt is essential for completing the catalytic cycle. Our catalytic system underwent fluorination exclusively with tertiary alkyl bromides and did not react with primary alkyl bromides, indicating that this stereospecific fluorination methodology is suitable for synthesizing fluorinated building blocks possessing stereo-defined F-containing tertiary carbon stereogenic center.     

Silver-catalyzed benzylation and allylation reactions of tertiary and secondary alkyl halides with grignard reagents

Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers.     

Nickel-catalyzed Kumada cross-coupling reactions of tertiary alkylmagnesium halides and aryl bromides/triflates

We report a Ni-catalyzed process for the cross-coupling of tertiary alkyl nucleophiles and aryl bromides. This process is extremely general for a wide range of electrophiles and generally occurs with a ratio of retention to isomerization >30:1. The same procedure also accommodates the use of aryl triflates, vinyl chlorides, and vinyl bromides as the electrophilic component.     

Steric Effects on Reaction Rates. Part XII. Force-Field Calculations for the Solvolysis of Cyclobutyl and Tricyclyl Derivatives

Force-field parameters have been developed for the molecular-mechanics calculation of tertiary carbenium ions with tricyclane structure, for tertiary cyclobutyl and cubyl cations. The cyclobutyl parameters are also applicable to tertiary 7-norbornyl cations. Satisfactory plots are obtained for correlation of the rates of solvolysis with the differences in steric energies between carbenium ions and the corresponding bromides.     

Catalytic asymmetric addition of alkylzinc and functionalized alkylzinc reagents to ketones

We describe our full report of the catalytic asymmetric addition of simple and functionalized dialkylzinc reagents to a broad range of saturated ketones and enones. The functionalized organozinc reagents contain esters, silyl ethers, alkyl chlorides, and alkyl bromides. In general, the resulting tertiary alcohol products are isolated with high ee's. With some substrates, yields are low as a result of the formation of aldol byproducts. Most substrates undergo additions with good yields reaching as high as 91%.     

CsOH-promoted P-alkylation: a convenient and highly efficient synthesis of tertiary phosphines

A mild and efficient method for the synthesis of tertiary phosphines and ditertiary phosphines has been developed. In the presence of cesium hydroxide, molecular sieves and DMF at room temperature, various secondary phosphines and alkyl bromides were examined, and the results have demonstrated that this methodology offers a general synthetic procedure to produce tertiary phosphines in moderate to high yields. Optically active tertiary phosphine synthesis is also described.     

Cobalt-catalyzed reductive coupling of saturated alkyl halides with activated alkenes

[reaction: see text] An efficient cobalt-catalyzed reductive coupling reaction of alkyl halides with electron-withdrawing alkenes (CH(2)=CR(1)EWG, EWG = electron-withdrawing group) in the presence of water and zinc powder in acetonitrile to give the corresponding Michael-type addition product (RCH(2)CR(1)EWG) was described. The methodology is versatile such that unactivated primary, secondary, and tertiary alkyl bromides and iodides and various conjugated alkenes including acrylates, acrylonitrile, methyl vinyl ketone, and vinyl sulfone all successfully participate in this coupling reaction. For the alkyl halides used in the reaction, the iodides generally gave better yields compared to those of the corresponding bromides. It is a unique method employing CoI(2)dppe, zinc, and alkyl halides, affording conjugate addition products in high yields. Mechanistically, the reaction appears to follow an oxidative addition driven route rather than the previously reported radical route.     

Intermolecular Photocatalyzed Heck‐like Coupling of Unactivated Alkyl Bromides by a Dinuclear Gold Complex

A practical protocol for a photocatalyzed alkyl‐Heck‐like reaction of unactivated alkyl bromides and different alkenes promoted by dinuclear gold photoredox catalysis in the presence of an inorganic base is reported. Primary, secondary, and tertiary unactivated alkyl bromides with β‐hydrogen can be applied. Esters, aldehydes, ketones, nitriles, alcohols, heterocycles, alkynes, alkenes, ethers, and halogen moieties are all well tolerated. In addition to 1,1‐diarylalkenes, silylenolethers and enamides can also be applied, which further increases the synthetic potential of the reaction. The mild reaction conditions, broad substrate scope, and an excellent functional‐group tolerance deliver an ideal tool for synthetic chemists that can even be used for challenging late‐stage modifications of complex natural products.     

Silver-catalyzed cross-coupling reactions of alkyl bromides with alkyl or aryl Grignard reagents

Treatment of secondary or tertiary alkyl bromides with alkyl Grignard reagents in the presence of catalytic amounts of silver bromide and potassium fluoride in CH₂Cl₂ afforded the corresponding cross-coupling products in reasonable yields. Moreover, silver showed catalytic activity for the cross-coupling reactions of alkyl bromides with aryl Grignard reagents.     

Selective Radical Fluorination of Tertiary Alkyl Halides at Room Temperature

Direct fluorination of tertiary alkyl bromides and iodides with Selectfluor is described. The halogen‐exchange fluorination proceeds efficiently in acetonitrile at room temperature under metal‐free conditions and exhibits a wide range of functional group compatibility. Furthermore, the reactions are highly selective in that alkyl chlorides and primary and secondary alkyl bromides remain intact. A radical mechanism is proposed for this selective fluorination.     

Alkylation of tertiary arsines with methylene bromide and subsequent anion exchange

Tertiary arsines react with methylene bromide to give (bromomethyl)trialkyl(aryl)arsonium bromides. Treatment of the latter with magnesium perchlorate in aqueous ethanol solutions leads to anion exchange forming the corresponding tertiary arsonium perchlorates in nearly quantitative yields.     

A Convenient Method of Esterification of Fatty Acids. Preparation of Alkyl Esters,Sterol Esters,Wax Esters and Triacylglycerols

A quick and mild, one-pot method of esterification of fatty acids with primary, secondary and tertiary alcohols as well as with fatty alcohols, sterols and glycerol is proposed via the acyl bromides formed in situ.     

A direct functionalization of tertiary alkyl bromides with O-, N-, and C-nucleophiles

Silver oxide used in stoichiometric amounts promoted the direct functionalization of tert-alkyl bromides and provided the desired adducts in 39-96% isolated yield. Reaction of tert-bromides with carboxylic acids yielded esters, with alcohols and phenols yielded alkyl and aryl ethers, with amines and anilines yielded selectively mono-alkylated amines and anilines, and with a C-nucleophile yielded an all-carbon quaternary hydrocarbon. The method was applied to a sequential alkylation of a primary amine with two different alkyl bromides yielding selectively a tertiary amine with three different substituents in one-pot.