Catalytic applications of transition metals in organic synthesis

Haughton, Louise; Williams, Jonathan M. J.

doi:10.1039/a909866f

Cited by 17 publications

(1 citation statement)

References 131 publications

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“…Transition metal mediated reactions have played a vital role in organic synthesis including synthesis of nitrogen heterocycles [1]. Coupled to this, there is a growing interest in solid state reactions, many of which are more efficient and selective than reactions in solution [2].…”

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A single pot synthesis of new dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]quinazolin-6-ols

Kumar¹,

Koul²,

Razdan³

et al. 2005

Journal of Heterocyclic Chemistry

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One pot synthesis of new unsymmetrical dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]-quinazolin-6-ols from 2-amino-5-phenyloxadiazole and salicylaldehydes, in solid phase, using Hg (II)-Al 2 O 3 catalyst, is described. The reaction is temperature sensitive, convenient, efficient and environmentally friendly.J. Heterocyclic Chem., 42, 487 (2005).Transition metal mediated reactions have played a vital role in organic synthesis including synthesis of nitrogen heterocycles [1]. Coupled to this, there is a growing interest in solid state reactions, many of which are more efficient and selective than reactions in solution [2]. During the recent past, the versatility of clays and adsorbents to act as solid supports and simultaneously catalyse these reactions, sometimes regiospecifically and stereospecifically [3], has been well recognized. However, the drawback of these reactions is the involvement of large quantities of solid supports. This drawback could be overcome by altering adsorbent surfaces with catalytic amounts of metals or their ions so that their catalytic activity is synergized.Our interest in developing new, cost-effective, convenient, and short methodologies for the synthesis of novel heteroaromatic compounds led us to envisage the synthesis of dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]quinazolin-6-ols with an oxygen bridge (2c - Substituted salicylaldehydes (2 -7) were made to react, in solid phase, with 2-amino-5-phenyloxadiazole, prepared by well known method [10], in the presence of Hg(II)-Al 2 O 3 catalyst at 110±5 °C. The reaction afforded unsymmetrical dimeric 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]quinazolin-6-ols 2c-7c (50-60%), with C-5, C-6 oxygen bridge between two quinazoline moieties, besides 2-amino(2-hydroxybenzylidene)-5-phenyl-1,3,4-oxadiazoles 2a-7a (5-10%) and 2-phenyl-10,3a-dihydro-1,3,4-oxadiazolino[3,2-a]quinazolin-6-ols 2b-7b (10-15%), (Table 1), which were characterized by spectral methods (IR, 1 H-NMR 13 C NMR and HREIMS). These observations led to the conclusion that the reaction proceeds through the initial formation of a Schiff's base, which underwent cyclisation via rearrangement of π bonds and hydrogen transfer, under the action of the catalyst, to the thermodynamically stable compounds 2b-7b. The dimeric products 2c-7c could possibly result from the, normally unexpected, addition of acidic phenol to the C=N bonds of the quinazoline moiety of 2b-7b (Figure 1) in a fashion akin to the addition to the C=N bond of the benzophenanthridine alkaloid sanguinarine [11].The novelty of this procedure is that the synthesis of dimeric compounds, which would require a series of

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