Chromenes catalyst-free conditions

A simple, clean, and environmentally benign three-component process to the synthesis of 2-amino-4H-chromenes using A,A-dimethyl aminoethylbenzyldimeth-ylammoniumchloride, [PhCH MejN CHjCHjNMeJCl, as an efficient catalyst under solvent-free condition was reported by Chen et al. (Fig. 12.75) [45],... 

Mondal et al. reported the synthesis of a new robust, non-air-sensitive, metal-free triazine-functionalized mesoporous organocatalyst TFMO-1 (Figure 1.5) and successfully used this material as an excellent catalyst in the one-pot three-component condensation reactions for the syntheses of 2-amino-chromene derivatives under solvent-free conditions (Mondal et al., 2012). TFMO-1 is an easily separable heterogeneous organocatalyst devoid of metal ions and thus is highly desirable to address industrial and environmental concerns. 

Naimi-Jamal et al. reported that anhydrous piperazine is an efficient organocata-lyst for the preparation of 2-amino-4ff-pyrans 158 and tetrahydro //-chromenes 159 via a three-component condensation under solvent-free ball-milling conditions at ambient temperature [47]. Without the presence of the catalyst, the reaction of p-chlorobenzaldehyde, malononitrile, and ethyl acetoacetate did not take place, even by heating at 80°C. However, an excellent yield of products was obtained by ball milling... 

Ordered mesoporous silica containing triazine moieties (Figure 3), based on the SBA-15 structure, has also been reported as an efficient and a reusable catalyst for the synthesis of chromenes 20 xmder solvent-free reaction conditions (Scheme 12) [75]. The catalyst was prepared from 3-mercaptopropyl-grafted SBA-15 by thiol-ene click reaction with 2,4,6-triallyloxy-l,3,5-triazine. The characterization data of the solid demonstrated the total disappearance of C=C bonds in triazine moiety. This feature strongly suggested the formation of bridges between the triazine and the mesopore walls. 

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