4,4'-trimethylenedipiperidine as a nitrogen heterocycle solvent and/or catalyst: Liquid phase tandem Knoevenagel-Michael condensation.

Liquid phase tandem Knoevenagel-Michael condensation of various aromatic and heteroaromatic aldehydes with barbituric acid or 2-thiobarbituric acid and malononitrile was studied in a one-pot three-component reaction. For the first time, TMDP was employed as a safe and efficient solvent and/or catalyst in the liquid and aqueous ethanol medium, respectively, for the practical and eco-friendly Knoevenagel-Michael condensation. The reactions were carried out by using greener procedures, including a) the use of TMDP as an N-heterocycle organocatalyst in a green medium including water and ethanol (1:1 v/v) at reflux temperature, and b) the use of TMDP as a dual solvent-catalyst at 65 °C in the absence of any solvent. High to excellent yields of the desired pyrano[2,3- d ]pyrimidinones were obtained under the two earlier mentioned conditions. The current methodologies have advantages, including (a) avoiding hazardous, toxic, volatile, and flammable materials and solvents, (b) avoiding tedious processes, harsh conditions, and multiple steps for the preparation of catalysts, (c) using a less toxic and noncorrosive catalyst, (d) minimizing hazardous waste generation and simple workup process, and (e) high recyclability of TMDP. Another important result of this work is that the TMDP can be a promising alternative for toxic, volatile, and flammable base reagents such as piperidine and triethylamine in liquid phase organic syntheses owing to its unique properties such as being less toxic, nonflammable, and nonvolatile, and having a low melting point, broad liquid range temperature, high thermal stability, and safe handling and storage.

Application of nitrogen-rich porous organic polymer for the solid-phase synthesis of 2-amino-4H-benzo[b]pyran scaffolds using ball milling process.

This paper presents the efficient synthesis of 2-amino-4H-benzo[b]pyrans using mesoporous poly-melamine-formaldehyde as a polymeric heterogeneous catalyst. According to the principals of green chemistry, the reaction was performed by the planetary ball milling process at ambient and neat conditions. The heterogeneous catalyst could be reused up to five runs with no reducing of catalytic efficiency. A variety of substituted 2-amino-4H-benzo[b]pyrans were obtained in good to excellent yields under eco-friendly conditions. Other advantages of the current methodology include short reaction time, wide substrate-scope, and use of a metal-free polymeric catalyst. Also, the current method avoids the use of hazardous reagents and solvents, tedious workup and multi-step purification. This work revealed that porous organic polymers containing Lewis base sites having acceptor-donner hydrogen bonding functional groups, and high porosity could play a vital role in the promotion of the one-pot multicomponent reactions in the solid-phase synthesis.

A Green Alternative for Aryl Iodide Preparation from Aromatic Amines.

BACKGROUND: In continuation of our previous work and the applications of saccharin, we encouraged to investigate the one-pot synthesis of the aryl iodides by the diazotization of the arene diazonium saccharin salts. OBJECTIVE: Arene diazonium salts play an important role in organic synthesis as intermediate and a wide variety of aromatic compounds have been prepared using them. A serious drawback of arene diazonium salts is their instability in a dry state; therefore, they must be stored and handled carefully to avoid spontaneous explosion and other hazard events. METHODS: The arene diazonium saccharin salts were prepared as active intermediates in situ through the reaction of various aryl amines with tert-butyl nitrite (TBN) in the presence of saccharin (Sac-H). Then, in situ obtained intermediates were used into the diazotization step without separation and purification in the current protocol. RESULTS: A variety of aryl iodides were synthesized at a greener and low-cost method in the presence of TBN, Sac-H, glacial acetic acid, and TEAI. CONCLUSION: In summary, a telescopic reaction is developed for the synthesis of aryl iodides. The current methodology is safe, cost-effective, broad substrate scope, and metal-free. All used reagents are commercially available and inert to moisture and air. Also, the saccharine and tetraethylammonium cation could be partially recovered from the reaction residue, which reduces waste generation, energy consumption, raw material, and waste disposal costs.

Arene diazonium saccharin intermediates: a greener and cost-effective alternative method for the preparation of aryl iodide.

In the current protocol, the arene diazonium saccharin derivatives were initially produced from various substituted aromatic amines; subsequently, these intermediates were treated with a greener organic iodide for the preparation of the aryl iodide. We tried to choose low-cost, commercially available, biodegradable, recoverable, ecofriendly, and safe reagents and solvents. The arene diazonium saccharin intermediates could be stored in the liquid phase into a refrigerator for a long time with no significant loss activity. The outstanding merits of the current protocol (a) included the partial recovering of saccharin and tetraethylammonium salt, (b) reduce the use of solvents and the reaction steps due to eliminating separation and purification of intermediates, (c) good yield of the sterically hindered substrates, and (d) avoid the generation of heavy metal or corrosive waste.