Solid supports inorganic

The synthesis of imidazoles is another reaction where the assistance of microwaves has been intensely investigated. Apart from the first synthesis described since 1995 [40-42], recently a combinatorial synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles has been described on inorganic solid support imder solvent-free conditions [43]. Different aldehydes and 1,2 dicarbonyl compounds 42 (mainly benzil and analogues) were reacted in the presence of ammonium acetate to give the trisubstituted ring 43. When a primary amine was added to the mixture, the tetrasubstituted imidazoles were obtained (Scheme 13). The reaction was done by adsorption of the reagent on a solid support, such as silica gel, alumina, montmorillonite KIO, bentonite or alumina followed by microwave irradiation for 20 min in an open vial (multimode reactor). The authors observed that when a non-acid support was used, addition of acetic acid was necessary to obtain good yields of the products. 

Most of the parallel reactions described in Schemes 4.23 and 4.24 were performed as dry-media reactions, in the absence of any solvent. In many cases, the starting materials and/or reagents were supported on an inorganic solid support, such as silica gel, alumina, or clay, that absorbs microwave energy or acts as a catalyst for the reaction (see also Section 4.1). In this context, an interesting method for the optimization of silica-supported reactions has been described [83], The reagents were co-spotted neat or in solution onto a thin-layer chromatographic (TLC) plate. 

The synthesis of octylthiocyanate by reaction of n-octyl bromide with KSCN, and its subsequent isomerization to isothiocyanate, have been realized by use of TBAB under the action of MW irradiation. The effect of inorganic solid supports was studied (Si02, K10, graphite, NaCl) (Eq. 64). 

Vass, A. Toth, J. Pallai-Varsanyi, E. in Effect of Inorganic Solid Support for Microwave Assisted Organic Reactions, OR 19, presented at the Int. Conf. Microwave Chemistry, Prague, Czech Republic, Sept. 6-11,1998. 

The practical applications of NaBH4 reductions on mineral surfaces for in situ generated SchifFs bases have been successfully demonstrated. The solid-state reductive amination of carbonyl compounds on various inorganic solid supports such as alumina, clay, silica etc. and especially on K 10 clay surface rapidly afford secondary and tertiary amines [126]. Clay behaves as a Lewis acid and also provides water from its interlayers thus enhancing the reducing ability of NaBH4 [22],... 

To a solution of substituted hydrazides 2 (0.02 mol) in ethanol added inorganic solid support (10 g) at room temperature. Similarly inorganic support (8 g) was added in the solution of phenacyl bromide/4-chlorophenacyl bromide/4-amino phenacyl bromide 1 (0.01 mol) in dichloromethane. Adsorbed material was mixed properly, kept inside alumina bath and subjected to microwave irradiation for 60-120 s. On completion of the reaction as followed by TLC examination, the mixture was cooled to room temperature and then product was extracted into ethanol (2x15 mL). The filtrate was concentrated and recovering the solvent under reduced pressure afforded the product which was purified through recrystallization from ethanol-DMF mixture. 

G. Bram, A. Loupy, D. Villemin, Microwave Activation of Reactions on Inorganic Solid Supports. In Solid Supports and Catalysts in Organic Synthesis, K. Smith (Ed.), Ellis Horwood Pretenice Hall, London, 1992. 

Scheme 15.7 (a) Condensation of 2-methylquinoline-3,4-dicarboxylic anhydride with primary amines using inorganic solid support (b) application of the methodology to the synthesis of a small library of imide derivatives. 

Ando T, Inorganic solid supported reagents as acids and bases, Stud. Surf. Sci. Catal., 90 9-20, 1994. 

Microwave-assisted solvent-free synthesis of a quinoline-3,4-dicarboximide library on inorganic solid supports has recently been reported [103]. Wet clay KIO was shown to be the best medium for the condensation reaction between 2-methylquinoline -3,4-dicarboxylic anhydride and several primary amines. Micro-wave irradiation is essential for rapid and complete formation of imides (Scheme 8.35). 

Supported reagent. One limitation to potassium permanganate is the limited solubility in organic solvents. Solubilization with a crown ether is one solution (4,143) another is impregnation on an inorganic solid support such as a molecular sieve, silica gel, and certain clays. Although the factors responsible for the enhanced reactivity of this form of KMn04 are not understood, such materials are useful for oxidation. ... 

Kay, 1968 Messing and Weetall, 1970 Silman and Katchalski, 1966). In this application the enzymes are immobilized on polymeric or inorganic solid support surfaces. The substrate to be reacted then is made to flow over the catalytic surface. The principal advantages include (1) The enzymes do not remain in the product as a difficultly separable impurity, (2) the enzymes may be reused, reducing cost, and (3) under certain conditions the useful life of the enzyme is prolonged. (Hasselberger et al, 1974.)... 

One-pot synthesis of 4(3/f)-quinazoHnones from 48, amines, and formic acid (or orthoesters) was developed by Rad-Moghadam et al. in 1998 [162], and recently more detailed procedures using inorganic solid support and neat one-pot procedure under microwave irradiation have been developed by Dan-dia etal. [163] (Scheme 8), and Liu et al. [164]. Also facile one-pot synthesis of 2,4(lff,3H)-quinazolinediones has been developed recently as a green chemical procedure by Nikpour et al. [165]. 

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