Three-Component Cycloaddition To Synthesize Aziridines and 1,2,3-Triazolines

An Efficient Synthesis of Oxygen-Bridged Spirooxindoles via Microwave-Promoted Multicomponent Reaction

A microwave-promoted multicomponent reaction of isatins, α-amino acids and 1,4-dihydro-1,4-epoxynaphthalene is achieved under environmentally friendly conditions, delivering oxygen-bridged spirooxindoles within 15 min in good to excellent yields. The attractive features of the 1,3-dipolar cycloaddition are the compatibility of various primary amino acids and the high efficiency of the short reaction time. Moreover, the scale-up reaction and synthetic transformations of spiropyrrolidine oxindole further demonstrate its synthetic utility. This work provides powerful means to expand the structural diversity of spirooxindole as a promising scaffold for novel drug discovery.

Additive-free synthesis of fused tricyclic cyanoisoxazolidines using in situ formed cyanonitrones

Herein, we disclose the first report on the generation of cyanonitrone in situ from diazoacetonitrile and nitrosoarene, and its subsequent [3+2] cycloaddition with oxabicyclic alkenes to access fused tricyclic cyanoisoxazolidines. Further, this methodology could be extended to access fused tricyclic trifluoromethylated and phosphonylated isoxazolidines. Surprisingly, the reductive ring-opening of cyanoisoxazolidines was followed by a spontaneous lactonization to produce fused tricyclic amino lactones. Moreover, the N-O bond of the obtained tricyclic trifluoromethylated isoxazolidines could be cleaved to obtain 1,3-amino alcohols.

Ruthenium-Catalyzed [2 + 2] versus Homo Diels-Alder [2 + 2 + 2] Cycloadditions of Norbornadiene and Disubstituted Alkynes: A DFT Study

The ruthenium-catalyzed [2 + 2] and homo Diels-Alder [2 + 2 + 2] cycloadditions of norbornadiene with disubstituted alkynes are investigated using density functional theory (DFT). These DFT calculations provide a mechanistic explanation for observed reactivity trends with different functional groups. Alkynyl phosphonates and norbornadiene form the [2 + 2 + 2] cycloadduct, while other functionalized alkynes afford the respective [2 + 2] cycloadduct, in excellent agreement with experimental results. The computational studies on the potential energy profiles of the cycloadditions show that the rate-determining step for the [2 + 2] cycloaddition is the final reductive elimination step, but the overall rate for the [2 + 2 + 2] cycloaddition is controlled by the initial oxidative cyclization. Two distinct mechanistic pathways for the [2 + 2 + 2] cycloaddition, cationic and neutral, are characterized and reveal that Cp*RuCl(COD) energetically prefers the cationic pathway.

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes

Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate, which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers, which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

Computational study on the mechanism of the reaction of benzenesulfonyl azides with oxabicyclic alkenes

The reaction of benzenesulfonyl azides with oxabicyclic alkenes to form aziridines could either proceed via initial [3 + 2] cycloaddition to form triazoline intermediates which then leads to aziridines, or via initial dinitrogen cleavage of the benzenesulfonyl azide to afford a nitrene intermediate followed by addition of this nitrene species across the olefinic C-C bond of the oxabicyclic alkene. Calculations at the DFT M06-2X/6-311G(d,p) level indicate that the initial [3 + 2] cycloaddition reaction of benzenesulfonyl azide and oxabicyclic alkene has barriers of 15.0 kcal/mol (endo) and 10.3 kcal/mol (exo) and rate constants of 5.23 × 10³ s^-1 (endo) and 3.86 × 10⁶ s^-1 (exo) whereas the pathway involving initial formation of nitrene species has a high activation barrier of 39.2 kcal/mol and rate constant of 8.92 × 10^-12 s^-1, indicating that the reaction will go through the former route to form an exo triazoline intermediate. The exo triazoline can either undergo a concerted C-C, N-N bond cleavage to form a ring-opened intermediate, a reaction that has a barrier of 23.4 kcal/mol, followed by dinitrogen extrusion and C-C, C-N bond regeneration with barriers of 29.1 and 23.5 kcal/mol respectively to form endo aziridines, or it can undergo direct nitrogen extrusion to form the exo product, a reaction with a barrier of 38.3 kcal/mol. Since the rate-determining step of the former route is 9.2 kcal/mol more favored than the latter, the former route rate is favored. The rate constants of the rate-determining steps are 1.30 × 10^-5 s^-1 (endo) and 3.16 × 10^-11 s^-1 (exo), indicating that endo aziridine would be formed as the major product and this is in conformity with the experimental observations of Chen et al. (J. Org. Chem. 18:11863-11872, 2019). The position of substituents on the benzene group of the benzenesulfonyl azide affects the endo/exo diastereoselectivity.Graphical abstract.