Please login first
Indium-mediated Aroylation vía Arylstannanes. Theoretical and Experimental Study
, * , , ,
1  Departamento de Química, Instituto de Química del Sur (INQUISUR) CONICET-Universidad Nacional del Sur, Avda. Alem 1253, 8000 Bahía Blanca, Argentina

Abstract: Arylstannanes are valuable reagents for the regiospecific generation of C-C bonds. Recently, we have informed the synthesis of crowded benzophenones by the indium-assisted, solvent free reaction of arylstannanes with bulky benzoyl chlorides.1 In order to determine the scope of this reaction for the synthesis of benzophenones, we study the reaction, under similar conditions, of arylstannanes with benzoyl chlorides. Experimental results showed that the efficiency of the reaction depends on the electronic nature of the substituents as well as their relative position on the aromatic ring of the benzoyl chloride. A series of reactions carried out with (2,6-dimethylphenyl)trimethylstannane as model, showed that p-nitrobenzoyl chloride did not react and 3,5-dimethoxybenzoyl chloride gave a poor yield of ketone (10%); on the other hand, naphthoyl-, 2,4,6-trimethylbenzoyl- and 2,6-dimethoxybenzoyl chlorides gave the corresponding ketones in 65%, 58% y 55%, respectively. Taking into account that the reactions proceed through a SET from In(0) to the aroyl chloride generating an acyl radical,1 and with the purpose of explaining experimental results, we performed a theoretical analysis with DFT methods (GAUSSIAN03). Considering that the energy of LUMO is related with electron affinities and that, once the radical anion is formed, the C(O)Cl bond fragments generating the corresponding acyl radical, we thought that the Frontier MO\'s energy, the localization of spin density and the energy (Ea) involved in the fragmentation process would give valuable information about the reactivity observed.2 The computational study showed that naphthoyl chloride presents the lower π* MO energy. On the other hand, there is a large difference between the Ea of isomeric dimethoxybenzoyl chlorides. Meanwhile the fragmentation is spontaneous in isomer 2,6-, 7 Kcal/mol are required for the fragmentation of isomer 3,5-. 1 Lo Fiego, M. J.; Silbestri, G. F.; Lockhart, M. T.; Chopa, A. B. J. Org. Chem. 2011, 76, 1707-1714. 2 Dorn, V. B.; Badajoz, M. A.; Lockhart, M. T.; Chopa, A. B.; Pierini, A. B. J. Organomet. Chem. 2008, 693, 2458-62.
Keywords: Aroylations; Arylstannanes; DFT methods