Acyclic nitronate olefin cycloaddition (ANOC): regio- and stereospecific synthesis of isoxazolines

Visible-Light-Mediated Three-Component Strategy for the Synthesis of Isoxazolines and Isoxazoles

Isoxazolines and isoxazoles commonly serve as core structures of many therapeutic agents and natural products. However, the metal-free and catalysis-free strategy for the synthesis of these privileged motifs at room temperature remains a challenging task. Herein, we report a three-component strategy to afford diverse isoxazolines and isoxazoles via [3 + 2] cycloadditions of in situ-formed nitronates and olefins/alkynes under visible-light irradiation.

One-Pot Synthesis of Isoxazole-Fused Tricyclic Quinazoline Alkaloid Derivatives via Intramolecular Cycloaddition of Propargyl-Substituted Methyl Azaarenes under Metal-Free Conditions

A practical method was developed for the convenient synthesis of isoxazole-fused tricyclic quinazoline alkaloids. This procedure accesses diverse isoxazole-fused tricyclic quinazoline alkaloids and their derivatives via intramolecular cycloaddition of methyl azaarenes with tert-butyl nitrite (TBN). In this method, TBN acts as the radical initiator and the source of N-O. Moreover, this protocol forms new C-N, C-C, and C-O bonds via sequence nitration and annulation in a one-pot process with broad substrate scope and functionalization of natural products.

Polyfunctionalization of vicinal carbon centers and synthesis of unsymmetric 1,2,3,4-tetracarbonyl compounds

The synthesis and characterization of organic compounds with unusual atom or functional group connectivity is one of the main driving forces in the discovery of new synthetic methods that has raised the interest of chemists for many years. Polycarbonyl compounds are such compounds wherein multiple carbonyl groups are directly juxtaposed and influence each other's chemical reactivity. While 1,2-dicarbonyl or 1,2,3-tricarbonyl compounds are well-known in organic chemistry, the 1,2,3,4-tetracarbonyl motif remains barely explored. Herein, we report on the synthesis of such 1,2,3,4-tetracarbonyl compounds employing a synthetic strategy that involves C-nitrosation of enoldiazoacetates, while the diazo functional group remains untouched. This strategy not only leverages the synthesis of 1,2,3,4-tetracarbonyl compounds to an unprecedented level, it also accomplishes the synthesis of 1,2,3,4-tetracarbonyl compounds, wherein each carbonyl group is orthogonally masked. Combined experimental and theoretical studies provide an understanding of the reaction mechanism and rationalize the formation of such 1,2,3,4-tetracarbonyl compounds.

Photocatalytic Regioselective [2 + 2 + 1] Radical Annulation of Alkenes with tert-Butyl Nitrite and gem-Dihalides

A visible-light photocatalytic regioselective [2 + 2 + 1] radical annulation reaction of alkenes, tert-butyl nitrite, and gem-dihalides has been developed. The protocol provides an efficient and practical approach to obtain isoxazolines in good yields under mild conditions. Significantly, gem-dihalides serve as C1 synthons, while cheap tert-butyl nitrite acts as an ideal "N-O" synthon.

Photocatalytic Regioselective Difunctionalization of Alkenes with Diazo Compounds and tert-Butyl Nitrite: Access to γ-Oximino Esters

A visible-light photocatalytic regioselective difunctionalization of alkenes with diazo compounds and tert-butyl nitrite has been developed. The protocol provides an efficient approach to γ-oximino esters under mild conditions. Significantly, this transformation not only shows the good compatibility of nucleophilic diazo compounds and electrophilic tert-butyl nitrite but also displays diazo compounds generating alkyl radicals that preferred addition to alkenes over nitroso radicals.

Generation of azaarene nitrile oxides from methyl azaarenes and t-BuONO enabling the synthesis of furoxans and 1,2,4-oxadiazoles

A high-efficiency strategy for the synthesis of furoxans and 1,2,4-oxadiazoles has been developed, using tert-butyl nitrite (TBN) as the nitrogen source. Azaarene nitrile oxides were generated in situ via methyl azaarenes functionalization.

[2 + 2 + 1] Cycloaddition of N-tosylhydrazones, tert-butyl nitrite and alkenes: a general and practical access to isoxazolines

N-Tosylhydrazones have proven to be versatile synthons over the past several decades. However, to our knowledge, the construction of isoxazolines based on N-tosylhydrazones has not been examined. Herein, we report the first demonstrations of [2 + 2 + 1] cycloaddition reactions that allow the facile synthesis of isoxazolines, employing N-tosylhydrazones, tert-butyl nitrite (TBN) and alkenes as reactants. This process represents a new type of cycloaddition reaction with a distinct mechanism that does not involve the participation of nitrile oxides. This approach is both general and practical and exhibits a wide substrate scope, nearly universal functional group compatibility, tolerance of moisture and air, the potential for functionalization of complex bioactive molecules and is readily scaled up. Both control experiments and theoretical calculations indicate that this transformation proceeds via the in situ generation of a nitronate from the coupling of N-tosylhydrazone and TBN, followed by cycloaddition with an alkene and subsequent elimination of a tert-butyloxy group to give the desired isoxazoline.

Catalyst-Free Formation of Nitrile Oxides and Their Further Transformations to Diverse Heterocycles

The formation of nitrile oxides with diazocarbonyl compounds by nitrosyl transfer from tert-butyl nitrite under mild conditions and without the use of a catalyst or an additive is reported. This transformation is broadly applicable to the synthesis of furoxans by dimerization and isoxazoles and isoxazolines by cycloaddition. This methodology is also applied for the millimole-scale synthesis of two biologically active compounds. The formation of the nitrile oxide from a diazoacetamide is stable and confirmed experimentally.