Erzsebet Jablonkai

Advances and New Variations of the Hirao Reaction

Introduction ................................................................................. 282 1. Coupling of Aryl Halides or Other Aryl Derivatives with Dialkyl Phosphites, Secondary Phosphine Oxides and Related Derivatives in the Presence of Pd(0) P Complexes........................ 282 2. Couplings in the Presence of Catalysts Formed from Pd(II) Salts and P-ligands ................................................................................ 290 3. “Greener” Accomplishments......................................................... 300 4. Couplings in the Presence of Cu and Ni Salts ................................ 303 5. Forming P C Bonds via the Salts of the >P(O)H Reagent ............. 307 6. Conclusions .................................................................................. 311 References .................................................................................... 311

A “green” variation of the Hirao reaction: the P–C coupling of diethyl phosphite, alkyl phenyl-H-phosphinates and secondary phosphine oxides with bromoarenes using a P-ligand-free Pd(OAc)2 catalyst under microwave and solvent-free conditions

The P–C coupling of diethyl phosphite, alkyl phenyl-H-phosphinates, diphenylphosphine oxide and dialkylphosphine oxides with bromoarenes may be performed in the presence of a P-ligand-free Pd(OAc)2 catalyst and triethylamine under microwave-assisted (MW) and, in almost all cases, solvent-free conditions to afford diethyl arylphosphonates, alkyl diphenylphosphinates, aryldiphenylphosphine oxides and dialkylphenylphosphine oxides, respectively. This is the “greenest” accomplishment of the well-known Hirao reaction that has now been found to have general application for a broad spectrum of >P(O)H species with different reactivity and a great variety of substituted bromobenzenes. The alkyl phenyl-H-phosphinates were prepared by the MW-promoted alkylation of phenyl-H-phosphinic acid in the absence of any solvent.

Microwave-Assisted Organophosphorus Synthesis

The spread of microwave (MW) equipment has brought about a tremendous development in synthetic organic chemistry. This environmentally friendly methodology, associated often with solventless conditions, has also had a positive impact on organophosphorus chemistry, allowing new reactions to be carried out, or increasing the rate, selectivity and yield. In special cases, MW irradiation may replace phase transfer or other kinds of catalysts. Reactions, such as the derivatization of phosphinic acids, the inverse Wittig protocol, Diels– Alder cycloadditions, fragmentation-related phosphorylations, phospha-Michael additions, Kabachnik–Fields condensations, the addition of >P(O)H species to carbonyl compounds, substitution of

The Potential of Microwave in Organophosphorus Syntheses

GRAPHICAL ABSTRACT Abstract In this paper, our recent results in microwave (MW)-assisted organophosphorus chemistry have been summarized. First, the esterification and amidation of cyclic phosphinic acids are discussed to represent reactions that are practically impossible on conventional thermal heating. Then, our results on the alcoholysis of dialkyl phosphites are demonstrated to show reactions which are reluctant on simple heating, but proceed better on MW irradiation. This is followed by the alkylation of CH acidic compounds, where MW may substitute the phase transfer catalyst. It is also possible that MW and a phase transfer catalyst synergize each other. Finally, our recent findings on the P-ligand-free Hirao reaction under MW conditions are presented.

The synthesis of phosphinates : traditional versus green chemical approaches

Abstract Three alternatives are discussed in comparison with the classical esterification of phosphinic chlorides by reaction with alcohols. All novel methods, such as microwave (MW)-assisted direct esterification, MW-assisted phase transfer catalyzed alkylating esterification and the propylphosphonic anhydride-promoted esterification, start from phosphinic acids and offer different advantages and disadvantages. The methods are analyzed from green chemical point of view.

Cyclic Phosphinates by the Alkylation of a Thermally Unstable 1-Hydroxy-1,2- Dihydrophosphinine 1-Oxide and A 3-Hydroxy-3-Phosphabicyclo[3.1.0]Hexane 3-Oxide

Abstract 1-alkoxy-1,2-dihydrophosphinine oxides 4 may be prepared by the reaction of 1-hydroxy-1,2-dihydrophosphinine 1-oxide 3 with alkyl halides. The best results were obtained in boiling acetone in the presence of K2CO3. The outcome of the alkylation of 3-hydroxy-6,6-dichloro-3-phosphabicyclo[3.1.0]hexane 3-oxide 5 was dependent on temperature. Butylation at 56 °C in acetone using K2CO3 afforded mainly the expected phosphinate 6, but an increase in the temperature led to opening of the cyclopropane ring, resulting in the formation of 1-butoxy-1,2-dihydrophosphinine oxide 4a as the major product. GRAPHICAL ABSTRACT

Synthesis of n-butyl ester and n-butylamide of methyl-phenylphosphinic acid: Two case studies

ABSTRACT n-Butyl methyl-phenylphosphinate and methyl-phenylphosphinic n-butylamide were synthesized by different methods: the reaction of methyl-phenylphosphinic chloride with nBuOH or nBuNH2, respectively, the T3P®-promoted derivatization of methyl-phenylphosphinic acid with nBuOH or nBuNH2, the microwave-assisted direct esterification of the model phosphinic acid, and finally the alkylating esterification with n-butyl bromide under phase-transfer-catalytic and microwave-assisted conditions. The different methods, mostly elaborated by us, were compared from practical and environmentally friendly points of view. GRAPHICAL ABSTRACT

MW-Assisted P-C Coupling Reaction Using P-Ligand-Free Pd(OAc)2 Catalyst

GRAPHICAL ABSTRACT Abstract P-C coupling reactions of a variety of >P(O)H species with aryl bromides were found to take place under P-ligand-free microwave conditions.

Microwave-Assisted Esterification of Phosphinic Acids by Alcohols, Phenols, and Alkyl Halogenides

Abstract Cyclic phosphinic acids undergo direct esterification with alcohols at ca. 200°C under microwave conditions.

Synthesis of Organophosphorus Compounds under Microwave Conditions

A variety of reactions including esterifications, alkylations, additions, cycloadditions, fragmentations and condensations were carried out under microwave (MW) and solventless conditions, occasionally in IL-s. In a few cases, the reactions could only be accomplished only under MW conditions, but not on traditional heating. In certain instances, MW could substitute phase transfer catalysis, in other cases MW was synergetic with it.