Four-Component Synthesis of Polysubstituted Pyrazin-2(1H)-ones through a Ugi/Staudinger/Aza-Wittig/Isomerization Sequence

Stereoselective Synthesis of 12-Tetrazolyl Substituted (E)-5H-Quinazolino[3,2-a]quinazolines via Sequential Ugi-Azide/Staudinger/aza-Wittig/Addition/Ag(I)-Catalyzed Cyclization

A new efficient and stereoselective synthesis of 12-tetrazolyl substituted (E)-5H-quinazolino[3,2-a]quinazolines via sequential Ugi-azide/Staudinger/aza-Wittig/addition/Ag(I)-catalyzed cyclization was developed. The four-component reactions of 2-azidobenzaldehyde, 2-(alkynyl)benzenamine, isocyanide, and trimethylsilyl azide gave Ugi-azide intermediates, which were subsequently treated with triphenylphosphine and isocyanate to produce 12-tetrazolyl substituted (E)-5H-quinazolino[3,2-a]quinazolines in the presence of Ag(I) catalyst and K₂CO₃.

2(1H)-Pyrazinones from acyclic building blocks: methods of synthesis and further derivatizations

Pyrazinones (2(1H)-pyrazinones) are found as components of a range of natural substances and are involved in the preparation of a great number of bioactive molecules. Synthesis of such compounds, and analogues, requires knowledge of the heterocyclic properties of pyrazinones and, in particular, methods for their ring construction. This review deals with the strategies that have been developed for the synthesis of pyrazinones from acyclic precursors, especially α-amino acid-derived units, from the first examples in 1905 up to the most recent in 2021.

In situ generation of imines by the Staudinger/aza-Wittig tandem reaction combined with thermally induced Wolff rearrangement for one-pot three-component β-lactam synthesis

A new efficient protocol for diastereoselective three-component one-pot lactam synthesis involving the in situ generation of imines via the Staudinger/aza-Wittig tandem reaction combined with the Wolff-rearrangement and ketene-imine cycloaddition was developed to produce a series of 24 novel structurally diverse β-lactam- or 1,3-oxazine-products. It was shown that this synthesis can be performed both as a two step-procedure and true MCR with simultaneous loading of all reactants. The intramolecular version of the 1^st step provided facile access to seven-membered cyclic imines, which allowed further preparation of a series of rare tricyclic β-lactams. For the intermolecular version of the 1^st step (acyclic imine generation), it was shown that the outcome of the synthesis is different from that using pre-synthesized and isolated imines. Additionally, this is the first example of the implementation of the Staudinger/aza-Wittig tandem reaction for the preparation of four-membered heterocycles.

New efficient synthesis of polysubstituted 3,4-dihydroquinazolines and 4H-3,1-benzothiazines through a Passerini/Staudinger/aza-Wittig/addition/nucleophilic substitution sequence

A new efficient synthesis of polysubstituted 3,4-dihydroquinazolines and 4H-3,1-benzothiazines via sequential Passerini/Staudinger/aza-Wittig/addition/nucleophilic substitution reaction has been developed. The three-component Passerini reactions of 2-azidobenzaldehydes 1, benzoic acid (2), and isocyanides 3 produced the azide intermediates 4, which were treated sequentially with triphenylphosphine, isocyanates (or CS₂), and secondary amines to give polysubstituted 3,4-dihydroquinazolines 8 and 4H-3,1-benzothiazines 11 in good overall yields through consecutive Passerini/Staudinger/aza-Wittig/addition/nucleophilic substitution reactions.

One-pot and divergent synthesis of polysubstituted quinolin-2(1H)-ones and oxireno[2,3-c]quinolin-2(1aH,3H,7bH)-ones via sequential Ugi/Knoevenagel condensation/hydrolysis and Ugi/Corey–Chaykovsky epoxidation reactions

A new one-pot and divergent synthesis of multisubstituted quinolin-2(1H)-ones and oxireno[2,3-c]quinolin-2(1aH,3H,7bH)-ones was developed.