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.
Highlights
The chemistry of phosphonates has inspired an increasing interest following their synthetic and biological reputation
C-Pbond bondforformation is the addition of phosphite nucleophile across the carbon–carbon double mation is the addition of phosphite nucleophile across the carbon–carbon doublebond, bond, which phospha-Michael reaction
Developing a recoverable catalyst with a better activity, easier separation and effective recycling with a better yield is the goal of scientists
Summary
The chemistry of phosphonates has inspired an increasing interest following their synthetic and biological reputation. C-Pbond bondforformation is the addition of phosphite nucleophile across the carbon–carbon double mation is the addition of phosphite nucleophile across the carbon–carbon doublebond, bond, which phospha-Michael reaction [11,12] This reaction catalyzed metal oxides [13], acids [14], bases [15,16], radical initiator [17,18]. 23), as R af base base catalyst, works under thermomorphic conditions a feature of homogeneously works under thermomorphic conditions with a featurewith of homogeneously catalyzing catalyzing phospha-Michael addition at a high temperature in a neat reaction the phospha-Michael addition at a high temperature in a neat reaction where the where reactants reactants serve as the solvent, forming heterogeneous precipitation at a lower temperature.
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