Synthesis of N,N,O-Trisubstituted Hydroxylamines by Stepwise Reduction and Substitution of O-Acyl N,N-Disubstituted Hydroxylamines

Theoretical Analysis of a Three-Component Reaction between Two Diazo Compounds and a Hydroxylamine Derivative: Mechanism, Enantioselectivity, and Effect of Cooperative Catalysis

The mechanism, enantioselectivity, and effect of chiral phosphoric acid (CPA) cocatalyst were investigated by the density functional theory (DFT) for the three-component asymmetric aminohydroxylation between two diazo compounds and a hydroxylamine derivative. This type of cascade process is cooperatively catalyzed by Rh2(OAc)4 and CPA. The obtained results clearly indicate that the first step of the global reaction involves a nucleophilic attack at the nitrogen center of N-hydroxyaniline by rhodium-carbene intermediates producing imines. Subsequently, an enolate intermediate was recognized as the key species generated from the second diazo compound and the leaving benzyl alcohol (BnOH) fragment of the first step and in the presence of the same dirhodium catalyst. Then, the reaction is terminated by the asymmetric Mannich-type addition, delivering the aminohydroxylation products of an S-R conformation with the assistance of chiral phosphoric acid. The distortion/interaction analysis shows that the relative distortions of CPA and the enol play a vital role in the energy ordering of the stereocontrolling transition states (TSs). Furthermore, the influence of different substituents in CPA was fully rationalized by distortion/interaction analysis. This study opens up novel synthetic possibilities and improves the reaction predictability when exploring the related types of cooperatively catalyzed organic transformations.

Recent Advances in the Synthesis of Di- and Trisubstituted Hydroxylamines

As an underrepresented functional group in bioorganic and medicinal chemistry, the hydroxylamine unit has historically received little attention from the synthetic community. Recent developments, however, suggest that hydroxylamines may have broader applications such that a review covering recent developments in the synthesis of this functional group is timely. With this in mind, this review primarily covers developments in the past 15 years in the preparation of di- and trisubstituted hydroxylamines. The mechanism of the reactions and key features and shortcomings are discussed throughout the review.

Synthesis of 10-Aza-9-oxakalkitoxin by N-O Bond Formation

We describe a formal synthesis of 10-aza-9-oxakalkitoxin, the hydroxalog of the cytotoxic marine natural product kalkitoxin, that features Mukaiyama Markovnikov silyl peroxidation of a terminal alkene and N-O bond formation as the central enabling steps.

Synthesis of O-tert-Butyl-N,N-disubstituted Hydroxylamines by N-O Bond Formation

The reaction of magnesium amides with tert-butyl 2,6-dimethyl perbenzoate in tetrahydrofuran at 0 °C provides a method for the synthesis O-tert-butyl-N,N-disubstituted hydroxylamines by direct N-O bond formation with a broad functional group tolerance. Less sterically hindered magnesium amides require ortho,ortho-disubstitution on the perester electrophile component, whereas sterically encumbered magnesium amides perform comparably with either tert-butyl perbenzoate or tert-butyl 2,6-dimethyl perbenzoate. A reaction mechanism is presented to account for the observed reactivity.

Dual Functional Pd-Catalyzed Multicomponent Reaction by Umpolung Chemistry of the Oxygen Atom in Electrophiles

A Pd-catalyzed multicomponent reaction was developed by trapping oxomium ylide with nitrosobenzene via Pd-promoted umpolung chemistry. The Pd catalyst plays two important roles: diazo compound decomposed catalyst and Lewis acid for the activation of nitrosobenzene. This strategy provides some insight into a new way for discovery of multicomponent methodology to construct complex molecules. The developed method also provides rapid access to a series of O-(2-oxy) hydroxylamine derivatives, which exhibit good anticancer activity in osteosarcoma cells.

En Route to the Transformation of Glycoscience: A Chemist's Perspective on Internal and External Crossroads in Glycochemistry

Carbohydrate chemistry is an essential component of the glycosciences and is fundamental to their progress. This Perspective takes the position that carbohydrate chemistry, or glycochemistry, has reached three crossroads on the path to the transformation of the glycosciences, and illustrates them with examples from the author's and other laboratories. The first of these potential inflexion points concerns the mechanism of the glycosylation reaction and the role of protecting groups. It is argued that the experimental evidence supports bimolecular SN2-like mechanisms for typical glycosylation reactions over unimolecular ones involving stereoselective attack on naked glycosyl oxocarbenium ions. Similarly, it is argued that the experimental evidence does not support long-range stereodirecting participation of remote esters through bridged bicyclic dioxacarbenium ions in organic solution in the presence of typical counterions. Rational design and improvement of glycosylation reactions must take into account the roles of the counterion and of concentration. A second crossroads is that between mainstream organic chemistry and glycan synthesis. The case is made that the only real difference between glycan and organic synthesis is the formation of C-O rather than C-C bonds, with diastereocontrol, strategy, tactics, and elegance being of critical importance in both areas: mainstream organic chemists should feel comfortable taking this fork in the road, just as carbohydrate chemists should traveling in the opposite direction. A third crossroads is that between carbohydrate chemistry and medicinal chemistry, where there are equally many opportunities for traffic in either direction. The glycosciences have advanced enormously in the past decade or so, but creativity, input, and ingenuity of scientists from all fields is needed to address the many sophisticated challenges that remain, not the least of which is the development of a broader and more general array of stereospecific glycosylation reactions.

Diversity-Oriented Synthesis of N,N,O-Trisubstituted Hydroxylamines from Alcohols and Amines by N-O Bond Formation

Magnesium dialkylamides react with alcohol-derived 2-methyl-2-tetrahydropyranyl alkyl peroxides (MTHPs) in tetrahydrofuran at 0 °C to give N,N,O-trisubstituted hydroxylamines suitable for medicinal chemistry purposes in good to excellent yields. A wide range of secondary alkyl and aryl amines and primary and secondary alcohol-derived MTHPs are compatible with the described reaction which, coupled with the enormous diversity of commercially available alcohols and secondary amines, suggests broad applicability of the reaction in fragment-based library design.

N–O linkage in carbohydrates and glycoconjugates

The synthesis and chemical and physicochemical properties as well as biological and medical applications of various hydroxylamine-functionalized carbohydrate derivatives are summarized.