Novel Pd(ii)-catalysed N,O-bicyclisation as an efficient route to the 6-oxa-2-azabicyclo[3.2.1]octane skeleton

Beyond osmium: progress in 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes

Olefin 1,2-difunctionalization has emerged as a popular strategy within modern synthetic chemistry for the synthesis of vicinal amino alcohols and derivatives. The advantage of this approach is the single-step simplicity for rapid diversification, feedstock nature of the olefin starting materials, and the possible modularity of the components. Although there is a vast number of possible iterations of 1,2-olefin difunctionalization, 1,2-amino oxygenation is of particular interest due to the prevalence of both oxygen and nitrogen within pharmaceuticals, natural products, agrochemicals, and synthetic ligands. The Sharpless amino hydroxylation provided seminal results in this field and displayed the value in achieving methods of this nature. However, a vast number of new and novel methods have emerged in recent decades. This review provides a comprehensive review of modern advances in accomplishing 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes that move beyond osmium to a range of other transition metals and more modern strategies such as electrochemical, photochemical, and biochemical reactivity.

Bi(iii)-catalyzed aminooxygenation of propargyl amidines to synthesize 2-fluoroalkyl imidazole-5-carbaldehydes and their decarbonylations

The first example of main group metal Bi(iii)-catalyzed aminooxygenation of fluorinated propargyl amidines was developed to produce 2-fluoroalkyl imidazole-5-carbaldehydes in moderate to excellent yields, in which phenol played a critical role and could be recovered and recycled. In the presence of KOt-Bu, an unconventional decarbonylation occurred on the 2-fluoroalkyl imidazole-5-carbaldehydes.

Mechanistic study of the solvent-controlled Pd(ii)-catalyzed chemoselective intermolecular 1,2-aminooxygenation and 1,2-oxyamination of conjugated dienes

The different coordination modes in MeCN and DMSO solvents could clarify the origin of chemoselectivity.

Solvent-Controlled Pd(II)-Catalyzed Aerobic Chemoselective Intermolecular 1,2-Aminooxygenation and 1,2-Oxyamination of Conjugated Dienes for the Synthesis of Functionalized 1,4-Benzoxazines

Pd(II)-catalyzed intermolecular 1,2-aminooxygenation and 1,2-oxyamination of conjugated dienes have been developed. The chemoselective preparation of a variety of 2-functionalized and 3-functionalized 1,4-benzoxazine derivatives was accomplished via the adjustment of a coordinating solvent. Oxygen was successfully used in this oxidative difunctionalization of alkenes. Good yields and selectivities were obtained for most products. A product bearing a spiro structure was also obtained from a 2,3-disubstituted-1,3-diene.

Visible-Light Promoted Distereodivergent Intramolecular Oxyamidation of Alkenes

The visible-light-promoted diastereodivergent intramolecular oxyamination of alkenes is described to construct oxazolindinones, pyrrolidinones and imidazolidones via mild generation of primary amidyl radicals from functionalized hydroxylamines. A unique phenomenon of highly diastereoselective ring-opening of aziridines controlled by electron sacrifices was observed. Highly diastereoselective amino alcohols derivatives were obtained efficiently through this protocol in gram scales. The mechanistic studies suggested the isolatable anti-aziridine intermediates were generated quickly from primary amidyl radicals and the diastereoselectivities were controlled by pK_a values of the electron sacrifices.

Copper-catalyzed aminooxygenation of styrenes with N-fluorobenzenesulfonimide and N-hydroxyphthalimide derivatives

A copper-catalyzed aminooxygenation reaction of styrenes with N-fluorobenzenesulfonimide and N-hydroxyphthalimide derivatives has been developed. The aminooxygenation product could be converted into the corresponding alcohol or free amine through the cleavage of the N–O or C–N bond of the N-hydroxyphthalimide moiety.

Intramolecular oxidative palladium-catalyzed diamination reactions of alkenyl sulfamates: an efficient synthesis of [1,2,5]thiadiazolo-fused piperazinones

A palladium-catalyzed diamination domino process of sulfamates arising from glycine allylamides is reported.

mCPBA-mediated metal-free intramolecular aminohydroxylation and dioxygenation of unfunctionalized olefins

We report a mild and metal-free process to prepare a variety of 2-hydroxymethylpyrrolidine and oxolanimine compounds.

Recent advances in heterobimetallic palladium(ii)/copper(ii) catalyzed domino difunctionalization of carbon–carbon multiple bonds

The Pd(ii)/Cu(ii)-catalysed double functionalization of carbon–carbon multiple bonds in domino processes has emerged in recent years as a fruitful tool for the rapid synthesis of complex molecular scaffolds.

Asymmetric palladium-catalysed intramolecular Wacker-type cyclisations of unsaturated alcohols and amino alcohols

The palladium (II)-catalysed reactions of alkenols and aminoalkenols such as oxycarbonylations or bicyclisations are powerful methods for the construction of oxygen and nitrogen-containing heterocyclic compounds. This review highlights recent progress in the development of the asymmetric palladium(II)-catalysed Wacker-type cyclisations of unsaturated polyols and aminoalcohols. The scope, limitations, and applications of these reactions are presented.

Mechanistic analysis and optimization of the copper-catalyzed enantioselective intramolecular alkene aminooxygenation

The catalytic asymmetric aminooxygenation of alkenes provides an efficient and straightforward approach to prepare chiral vicinal amino alcohols. We have reported a copper(II)-catalyzed enantioselective intramolecular alkene aminooxygenation, using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as the oxygen source, which results in the synthesis of chiral indolines and pyrrolidines. Herein we disclose that kinetics studies indicate the reaction is first order both in substrate and the [Cu(R,R)-Ph-bis(oxazoline)]OTf(2) catalyst and zero order in TEMPO. Furthermore, kinetic isotope effect studies support that the cis-aminocupration step, the addition of N-Cu across the alkene, is the rate-limiting step. Subsequent formation of a carbon radical intermediate and direct carbon radical trapping with TEMPO is the indicated mechanism for the C-O bond formation as suggested by a deuterium labeling experiment. A ligand screen revealed that C(4)-phenyl substitution on the bis(oxazoline) is optimal for high asymmetric induction. The size of the substrate's N-sulfonyl group also influences the enantioselectivity of the reaction. The preparative-scale catalytic aminooxygenation reaction (gram scale) was demonstrated, and an unexpected dependence on reaction temperature was uncovered on the larger scale reaction.

Stereoselective synthesis of morpholines via copper-promoted oxyamination of alkenes

A new copper(II) 2-ethylhexanoate-promoted addition of an alcohol and an amine across an alkene (oxyamination) is reported. The alcohol addition is intramolecular, while coupling with the amine occurs intermolecularly. Several 2-aminomethyl morpholines were synthesized in good to excellent yields and diastereoselectivities.

Iron catalyzed asymmetric oxyamination of olefins

The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst.

Stereoselective Copper-Catalyzed Intramolecular Alkene Aminooxygenation: Effects of Substrate and Ligand Structure on Selectivity

A new protocol for diastereoselective copper-catalyzed intra-molecular alkene aminooxygenation, which provides methyleneoxy-functionalized disubstituted pyrrolidines and five-membered cyclic ureas from the corresponding γ-alkenyl sulfonamides and N-allylureas, is reported. In addition, some success was achieved in enantioselective desymmetrizations reactions. We discovered that the level of enantioselectivity and diastereoselectivity could be tuned by choice of copper(II) ligands and substrate N-substituent.

N-Nosyl Oxaziridines as Terminal Oxidants in Copper(II)-Catalyzed Olefin Oxyaminations

We report that N-4-nosyl-3-phenyloxaziridine is an effective terminal oxidant for copper(II)-catalyzed oxyamination recently developed in our labs. This oxaziridine can be prepared on multi-gram scale and is easily purified by recrystallization. The products of oxyamination using this oxaziridine bear protecting groups that can be readily removed in high yields under mild conditions.

Iron-catalyzed aminohydroxylation of olefins

We have discovered that N-sulfonyl oxaziridines react with a broad range of olefins in the presence of iron salts to afford 1,3-oxazolidines. This process provides access to 1,2-aminoalcohols with the opposite sense of regioselectivity produced from the copper-catalyzed oxyamination previously reported by our laboratories. Thus, either regioisomeric form of 1,2-aminoalcohols can easily be obtained from the reaction of oxaziridines with olefins, and the sense of regioselectivity can be controlled by the appropriate choice of inexpensive, nontoxic, first-row transition-metal catalyst.

Oxaziridine-mediated enantioselective aminohydroxylation of styrenes catalyzed by copper(II) bis(oxazoline) complexes

We report an oxaziridine-mediated enantioselective aminohydroxylation of olefins catalyzed by a chiral copper(II) bis(oxazoline) complex. A variety of styrenic olefins undergo efficient aminohydroxylation with excellent regioselectivity and synthetically useful levels of enantioselectivty (up to 84% ee). The reaction can be conducted on multi-gram scale with as little as 2 mol% of the copper(II) catalyst. Hydrolysis of the resulting 1,3-oxazolines under acidic conditions produces N-sulfonyl amino alcohols that can be purified by recrystallization to afford very high levels of enantioselectivity.

Diastereoselective pyrrolidine synthesis via copper promoted intramolecular aminooxygenation of alkenes: formal synthesis of (+)-monomorine

The diastereoselectivity of the copper-promoted intramolecular aminooxygenation of various alkene substrates was investigated. Alpha-substituted 4-pentenyl sulfonamides favor the formation of 2,5-cis-pyrrolidines (dr >20:1) giving excellent yields which range from 76-97% while gamma-substituted substrates favor the 2,3-trans pyrrolidine adducts with moderate selectivity (ca. 3:1). A substrate whose N-substituent was directly tethered to the alpha-carbon exclusively yielded the 2,5-trans pyrrolidine. The synthetic utility of the method was demonstrated by a short and efficient formal synthesis of (+)-monomorine.

Copper catalyzed enantioselective intramolecular aminooxygenation of alkenes

The copper-catalyzed enantioselective intramolecular aminooxygenation of alkenes is reported herein. This is the first report of an enantioselective intramolecular alkene aminooxygenation process. N-Arylsulfonyl-2-allylanilines and 4-pentenylarylsulfonamides cyclize in high yield and with good enantioselectivity, providing new chiral methyleneoxy-functionalized dihydroindolines and pyrrolidines. Tetramethylaminopyridyl radical (TEMPO) serves as both the source of the oxygen and the stoichiometric oxidant. These reactions are catalyzed by copper(II) triflate, complexed with (4S,5R)-Bis-Phbox. The unprotected aminoalcohols can be obtained by sequential dissolving metal reductions of the N-S and O-N bonds.