engleski

Two polymorphs of a Povarov cyclization product derived from a o-vanillaldimine

N-bromophthalimide (nbp) belongs to N-haloimides, a well-recognized group of commercially available compounds usually used as halogenation agents and catalysts in various cyclization or halolactonization reactions in organic chemistry (Nakatsuji et al., 2014). On the other hand, they have recently drawn attention due to their potential as halogen bond donors in the synthesis of cocrystals (Raatikainen & Rissanen, 2011 ; Mavračić et al., 2016). In effort to obtain cocrystals of nbp and an imine, derived from o-vanillin and 2-aminonaphthalene, we have obtained an aryl[f]quinoline as a product of the Povarov reaction (Povarov, 1967) with acetone. We first attempted the grinding of nbp and imine in the stoichiometric ratio 1:1 in a ball mill. After 10 minutes of grinding under normal laboratory conditions (temperature ca. 25 °C, 40–50% RH) the resulting solid was dissolved in acetone. The solution was allowed to evaporate slowly overnight at room temperature, yielding single crystals of two polymorphs. Crystal structure determination revealed that the prepared polymorphs display interesting and remarkably different molecular packing features. In the crystal structure of form 1, the molecules are connected into centrosymmetrical R22(18) dimers via C–H∙∙∙O(hydroxy) hydrogen bonds and further connected by C–H∙∙∙C hydrogen bonds into a 3D-network. In the crystal structure of form 2, the molecules are connected into centrosymmetrical R22(8) dimers via C–H∙∙∙O(methoxy) hydrogen bonds. By means of Br∙∙∙O contacts (d = 3.377 Å) of the same distance as the sum of the van der Waals radii of bromine and oxygen and C–H∙∙∙C hydrogen bonds 2D-sheets are formed.

N-bromophthalimide ; mechanochemistry ; polymorphism ; Povarov reaction

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