Phospha-Michael addition of phosphorus nucleophiles to α,β-unsaturated malonates using 3-aminopropylated silica gel as an efficient and recyclable catalyst
Graphical abstract
3-Aminopropylated silica gel, is introduced as an efficient and recyclable catalyst for the phospha-Michael addition of phosphorus nucleophiles to α,β-unsaturated malonates. Short reaction times, mild reaction conditions, ease of recovery and catalyst reusability make this method a new, economic and waste-free chemical process for the synthesis of β-phosphonomalonates.
Research highlights
► β-Phosphono malonates were synthesized by phospha-Michael addition reaction. ► Phospha-Michael addition reaction was efficiently catalyzed by 3-aminopropylated silica gel. ► Different phosphite esters reacted with α,β-unsaturated malonates.
Introduction
Owing to the synthetic and biological values of phosphonates, their chemistry has stimulated an increasing interest and the development of new methodologies for their preparation is an important goal in organic synthesis [1], [2], [3], [4]. Phosphonoacetic acid [5], [6], [7], [8] has been shown to inhibit the replication of cytomegalovirus and herpes virus by interacting directly with the virus-induced DNA polymerase. Phosphonoformate [9] has shown activity in cell cultures against HTLV-III (the virus implicated in AIDS), and a derivative of β-phosphonomalonic acid [10] was used as an inhibitor of ras farnesyl protein transferase in studies directed toward the development of new antitumor agents. Phosphonate monosalts have shown good herbicide activities and demonstrated as an inhibitor of pyruvate dehydrogenase [11]. Phosphonates have been also used to synthesize different organometallic compounds such as silicon, tin and iron complexes. In these kinds of complexes, metal coordinated to high donating phosphoryl group or an alkenyl group in phosphonates [12], [13], [14].
Direct phosphorus–carbon bond formation represents one of the most versatile and powerful tools for the synthesis of phosphonates. Amongst these methods, phospha-Michael addition, that is, the addition of a phosphorus nucleophile to an electron-deficient alkene has evoked remarkable attention by organic chemists [15], [16]. This kind of phosphorus–carbon bond formation most commonly promoted by bases [15], [16], [17], [18], [19], Brønsted/Lewis acids [20], [21], microwaves [22], transition metals [23], [24] and radical initiators such as AIBN [25], [26]. Even though phospha-Michael addition could proceed by these methods, many of these reagents cannot be re-used and in many instances, long reaction times, drastic reaction conditions and sometimes, according to the nature of the catalyst, tedious workup is needed. Additionally, in most of these methods, malodorous trialkyl phosphite was used as the phosphorus nucleophile. Thus, it is necessary to further develop an efficient and convenient method for the synthesis of such significant scaffold.
Use of heterogeneous solid base catalysts is of current interest in chemistry and industry because solid bases offer many advantages such as simplicity in handling, more environmentally safe disposal and less plant corrosion problems [27], [28]. Amine functionalized silica gel such as 3-aminopropylated silica gel (AP-SiO2) is one of the organic–inorganic hybrid materials that have been applied as effective solid base catalyst in organic transformations [27], [28], [29], [30]. In these types of solid base catalysts, the reactive centres are highly mobile similar to that of homogeneous catalysts and at the same time these species have the advantage of being recyclable in the same fashion as heterogeneous catalysts.
Section snippets
Results and discussion
As part of our ongoing program directed toward the development of new methods for the synthesis of phosphonate derivatives [31], [32], [33], [34], [35], recently we have introduced HClO4/SiO2 as an efficient catalyst for the synthesis of β-phosphonomalonates via phospha-Michael addition of trialkyl phosphite to α,β-unsaturated malonates [36]. This acidic condition was not appropriate for the phospha-Michael addition of diethyl phosphite as an odorless phosphorus nucleophile to
Conclusion
In summary, AP-SiO2 was found as a new, re-usable and efficient catalyst for the synthesis of a variety of β-phosphonomalonates by phospha-Michael addition of phosphite esters with different α,β-unsaturated malonates. Good to high yields, short reaction times, use of dialkyl phosphite instead of malodorous trialkyl phosphite, simple workup, ease of catalyst recovery, no by-product formation and reusability of the catalyst without appreciable loss of activity make this method attractive and a
Materials and physical measurements
Chemicals were purchased from Merck and Fluka Chemical Companies. AP-SiO2 was prepared by known procedures [29], [30]. The percentage of supported nitrogen atoms on silica gel (1.35%) was obtained by elemental analysis. α,β-Unsaturated malonates were prepared by a known procedure [41]. All of the products were identified by their physical and spectral data. NMR spectra were recorded on a Bruker Avance DPX-250. Mass spectra were recorded on a Shimadzu GCMS-QP5050A. The purity of the products and
Acknowledgment
We are thankful to Birjand University Research Council for their support of this work.
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2020, Molecular CatalysisCitation Excerpt :But the acidic condition was not suitable for this reaction leading to poor yield of product and longer reaction time. [134] Therefore, later they synthesized 3-aminopropylated silica gel (AP-SiO2) as a basic catalyst for the same reaction (Fig. 16) (Scheme 7). [135] Phospha-Michael addition of diethyl phosphite to benzylidenemalononitrile as a model reaction was carried out.
Aqueous microwave-assisted DMAP catalyzed synthesis of β-phosphonomalonates and 2-amino-4H-chromen-4-ylphosphonates via a domino Knoevenagel-phospha-Michael reaction
2017, Comptes Rendus ChimieCitation Excerpt :Variety of catalysts as clay-supported heteropolyacid [12], γ-Fe2O3-pyridine based catalyst [13], 3-aminopropylated silica gel [14], sodium stearate [15], HClO4–SiO2 [16], Fe-doped single walled carbon nanotubes [17], lanthanum(III) triflate supported on nanomagnetic γ-Fe2O3 [18], polystyrene-supported DABCO [19] pyridine-grafted graphene oxide [20], quaternary ammonium salt [H-dabco][AcO] [21], di-n-butylamine [22], nanosized zinc oxide [23], Phosphomolybdic acid [24], have been employed for the synthesis of β-phosphonomalonates. Further, catalysts like nano-MgO [25], sulfochitosan encapsulated nano-Fe3O4, [26] ionic liquid [Bmim]OH [27], PEG [28], potassium phosphate [29], β-cyclodextrin [30], InCl3 [31], and electrochemical approach [32] have been used for the synthesis of 2-amino-4H-chromen-4-ylphosphonates. Importantly, to the best of our knowledge, there are only few reports on the use of common catalysts [33–38] for the construction of both β-phosphonomalonates and 2-amino-4H-chromen-4-ylphosphonates scaffolds.