Phosphine-Catalyzed Reaction between 2-Aminobenzaldehydes and Dialkyl Acetylenedicarboxylates: Synthesis of 1,2-Dihydroquinoline Derivatives and Toward the Development of an Olefination Reaction

Facile synthesis of 2-vinylindolines via a phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process

A novel phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process between o-aminobenzaldehydes and Morita-Baylis-Hillman (MBH) carbonates has been ingeniously developed. This protocol serves as a practical tool for the facile synthesis of a broad range of 2-vinylindolines in moderate to good yields under mild reaction conditions. The applicability of this method was demonstrated with gram-scale reaction and various transformations of the corresponding product.

Rapid Assembly of Functionalized 2H-Chromenes and 1,2-Dihydroquinolines via Microwave-Assisted Secondary Amine-Catalyzed Cascade Annulation of 2-O/N-Propargylarylaldehydes with 2,6-Dialkylphenols

An efficient, secondary amine-catalyzed cascade annulation of 2-O/N-propargylarylaldehydes with 2,6-dialkylphenols was established to access biologically relevant functionalized 2H-chromenes and 1,2-dihydroquinolines tethered with a synthetically useful p-quinone methide scaffold in high yields under microwave irradiation and conventional heating conditions. The microwave-assisted strategy was convenient, clean, rapid, and high yielding in which the reactions were completed in just 15 min, and the yields obtained were up to 95%. This highly atom-economical domino process constructed two new C-C double bonds and a six-membered O/N-heterocyclic ring in a single synthetic operation. Its mechanism process was rationalized as involving sequential iminium ion formation, nucleophilic addition, and intramolecular annulation steps. Furthermore, the synthesized 2H-chromene derivatives were transformed into valuable indeno[2,1-c]chromenes, 5H-indeno[2,1-c]quinolines, and oxireno[2,3-c]chromene via a palladium-catalyzed double C-H bond activation process and epoxidation, respectively.

Fluorinated 2-Azetines: Synthesis, Applications, Biological Tests, and Development of a Catalytic Process

An efficient and straightforward phosphine-promoted tandem aza-Michael addition/intramolecular Wittig reaction was developed for the synthesis of polyfunctionalized 2-azetines. After demonstrating that this transformation could be made catalytic in phosphine through in situ reduction of phosphine oxide with phenylsilane, different post-transformation steps have been demonstrated, including an original [2 + 2] photodimerization. Preliminary biological tests highlighted that these fluorinated 1,2-dihydroazete-2,3-dicarboxylates exhibited significant cytotoxicity against the human tumor cell line.

Ru(II)-Catalyzed Decarbonylative Alkylation and Annulations of Benzaldehydes with Iodonium Ylides under Chelation Assistance

A Ru(II)-catalyzed decarbonylative alkylation and annulation of salicylaldehydes and 2-aminobenzaldehydes with iodonium ylides has been developed for the synthesis of dibenzo[b,d]furans and NH-free carbazolones. The reaction proceeds smoothly under mild conditions with a low catalyst loading and a broad substrate compatibility. Notably, hydroxy and free amino groups were demonstrated to be the effective directing groups, enabling the successful aldehyde C-H bond activation and subsequent decarbonylation and annulation under the inexpensive Ru(II) catalyst.

Phosphine-Mediated Morita-Baylis-Hillman-Type/Wittig Cascade: Access to E-Configured 3-Styryl- and 3-(Benzopyrrole/furan-2-yl) Quinolinones

A phosphine-mediated, well-designed Morita-Baylis-Hillman-type/Wittig cascade for the rapid assembly of a quinolinone framework from benzaldehyde derivatives is developed for the first time. By rationally combining I₂/NIS-mediated cyclization, biologically relevant 3-(benzopyrrole/furan-2-yl) quinolinones were facilely synthesized in a one-pot process by starting from 3-styryl-quinolinones bearing an o-hydroxy/amino group, significantly expanding the chemical space of this privileged skeleton. Further utility of this protocol is illustrated by successfully performing this transformation in a catalytic manner through in situ reduction of phosphine oxide by phenylsilane.

Metal-free synthesis of quinoline-2,4-dicarboxylate derivatives using aryl amines and acetylenedicarboxylates through a pseudo three-component reaction

An efficient, useful and one-pot protocol for the synthesis of quinoline-2,4-dicarboxylate scaffolds is accomplished from aryl amines and dimethyl/diethyl acetylenedicarboxylates using 20 mol% molecular iodine as a catalyst in acetonitrile at 80 °C. In addition, the mechanistic explanation for the formation of the desired products is disclosed. The pivotal role of molecular iodine in the formation of the major products, diester quinoline derivatives, and the minor product, triesters, in two cases is described in the mechanism. The notable advantages of this method are non-involvement of a metal catalyst, avoiding of metal contamination in the final product as well as waste generation, use of a low cost and eco-friendly catalyst, ease of handling, high regioselectivity, shorter reaction time, the formation of one C-N and two C-C bonds and a broad substrate scope with good yields.

Metal-Free Deoxygenation of Amine N-Oxides: Synthetic and Mechanistic Studies

We report herein an unprecedented combination of light and P(III)/P(V) redox cycling for the efficient deoxygenation of aromatic amine N-oxides. Moreover, we discovered that a large variety of aliphatic amine N-oxides can easily be deoxygenated by using only phenylsilane. These practically simple approaches proceed well under metal-free conditions, tolerate many functionalities and are highly chemoselective. Combined experimental and computational studies enabled a deep understanding of factors controlling the reactivity of both aromatic and aliphatic amine N-oxides.

Phosphorus-Based Catalysis

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

A series of 1-substituted-3-methyl-2-phospholene oxides was prepared from the corresponding 3-phospholene oxides by double bond rearrangement. The 2-phospholene oxides could be obtained by heating the 3-phospholene oxides in methanesulfonic acid, or via the formation of cyclic chlorophosphonium salts. Whereas mixtures of the 2- and 3-phospholene oxides formed, when the isomerization of 3-phospholene oxides was attempted under thermal conditions, or in the presence of a base. The mechanisms of the various double bond migration pathways were elucidated by quantum chemical calculations.

Convergent Synthesis of Polysubstituted Furans via Catalytic Phosphine Mediated Multicomponent Reactions

Tri- or tetrasubstituted furans have been prepared from terminal activated olefins and acyl chlorides or anhydrides by a multicomponental convergent synthesis mode. Instead of stoichiometric nBu₃P, only catalytic nBu₃P or nBu₃P=O is needed to furnish the furans in modest to excellent yields with a good functional group tolerance under the aid of reducing agent silane. This synthetic method features a silane-driven catalytic intramolecular Wittig reaction as a key annulation step and represents the first successful application of catalytic Wittig reaction in multicomponent cascade reaction.

Glycoconjugates via phosphorus ylides

A facile, high yielding access to rare chimeric compounds combining phosphorus ylides with complex glycosyl formamides is described. We determined x-ray structures gaining structural insight into this compounds class. In addition, data mining of similar compounds deposited within the Cambridge Structural Database was performed. These derivatives could be used either as synthetic intermediates via the ylide functionalization and glyco chemical biology synthons or improving the pharmacokinetic properties of a potential bioactive molecule, exploiting the glycosyl moiety.