Recoverable Phospha-Michael Additions Catalyzed by a 4-N,N-Dimethylaminopyridinium Saccharinate Salt or a Fluorous Long-Chained Pyridine: Two Types of Reusable Base Catalysts

Abstract

Phospha-Michael addition, which is the addition reaction of a phosphorus-based nucleophile to an acceptor-substituted unsaturated bond, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds, since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalized products. In this work, two kinds of basic pyridine-based organo-catalysts were used to efficiently catalyze phospha-Michael addition reactions, the 4-N,N-dimethylaminopyridinium saccharinate (DMAP·Hsac) salt and a fluorous long-chained pyridine (4-Rf-CH2OCH2-py, where Rf = C11F23). These catalysts have been synthesized and characterized by Lu’s group. The phospha-Michael addition of diisopropyl, dimethyl or triethyl phosphites to α, β-unsaturated malonates in the presence of those catalysts showed very good reactivity with high yield at 80–100 °C in 1–4.5 h with high catalytic recovery and reusability. With regard to significant catalytic recovery, sometimes more than eight cycles were observed for DMAP·Hsac adduct by using non-polar solvents (e.g., ether) to precipitate out the catalyst. In the case of the fluorous long-chained pyridine, the thermomorphic method was used to efficiently recover the catalyst for eight cycles in all the reactions. Thus, the easy separation of the catalysts from the products revealed the outstanding efficacy of our systems. To our knowledge, these are good examples of the application of recoverable organo-catalysts to the DMAP·Hsac adduct by using non-polar solvent and a fluorous long-chained pyridine under the thermomorphic mode in phospha-Michael addition reactions.

New Horizon in Phospha-Michael Reaction: Ultrafast Double Addition of P–H Bond-Bearing Nucleophiles to Electron-Deficient Triple Bonds and Its Use for Functional Monomer Synthesis and Polymer Modification

“…The dissolution−precipitation (CHCl 3 −Et 2 O) procedure was repeated two times, and the recovered polymer was dried overnight in a vacuum oven at 40 °C (yield: 630 mg, 88%). 1…”

“…The phospha-Michael reaction, which is the addition of a phosphorus nucleophile (Michael donor) to an electron-deficient unsaturated structure containing an electron-withdrawing group (Michael acceptor), is a versatile and powerful tool for P–C bond formation. − It is regarded as a straightforward and environmentally friendly technique and has been intensively investigated and utilized for the synthesis of various organophosphorus compounds for a wide range of applications. − The efficiency of the phospha-Michael addition depends heavily on the nucleophilicity of the phosphorus-based species, the structure of the unsaturated alkene/alkyne, and the catalysts used as well as the reaction conditions such as temperature and solvent . So far, several catalysts and solvent systems have been suggested for various phosphorus nucleophiles and unsaturated molecules. − While the addition of phosphorus nucleophiles to alkenes bearing electron-withdrawing groups such as acrylates is much more widely explored, the studies regarding the triple bond-containing analogues are quite few. ,− The latter reactions are also known as phospha-yne or Pudovik reactions in the literature. , Recently, Adlu et al reported the reaction of acetylenedicarboxylic acid esters with different phosphites in the presence of NaCN in aqueous acetone .…”

Promiscuous Lipase-Catalyzed Knoevenagel–Phospha–Michael Reaction for the Synthesis of Antimicrobial β-Phosphono Malonates

“…Many of these two-component protocols essentially involve the addition of phosphite nucleophiles to benzylidine malononitrile; however, reports on the multicomponent one-pot synthesis of β-phosphonomalononitriles which eliminate the need for α,β-unsaturated malonates derivatives are highly limited [ 26 , 27 , 28 ]. Unfortunately, many of the reported protocols suffer from some inconveniences, such as the stoichiometric amount of catalysts, water free environment, or the application of expensive and highly toxic catalysts [ 29 , 30 ]. Moreover, some of the available methods lead to obtaining products contaminated with metals, which significantly reduces their applicability in the synthesis of biologically active compounds.…”