COMe Ph Ph Me O Ph Ph Ph Ph + TCS room temp. EtOH 7 + 8 (1) Me O 11,12 NO2 NO2 NO2 COMe + TCS EtOH room temp. (2) O2N O H Me NO2 O2N O H Me NO2 ( E)-12a ( Z)-12b R Me R O R R R 1 R = H 3 R = 4-Cl 5 R = 4-Br 9 R = 4-OMe 2 R = H 4 R = 4-Cl 6 R = 4-Br 10 R = 4-OMe 232 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 232–233 J. Chem. Research (M), 1997, 1537–1544 A New Approach to the Stereoselective Synthesis of b-Methylchalcones Saad S. Elmorsy,* Abdel Galel M. Khalil, Margret M.Girges and Tarek A. Salama Chemistry Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt Many b-methylchalcone derivatives are prepared via the self condensation of aralkyl ketones mediated by tetrachlorosilane–ethanol under mild conditions. The present study is concerned with the elaboration of a highly efficient and stereodefined synthesis of b-methylchalcones. Unlike titanium tetrachloride, the reaction of aryl methyl ketone with an equimolar amount of tetrachlorosilane (TCS) in the presence of absolute ethanol and in the absence of catalyst afforded a b-methylchalcone along with a smaller amount of 1,3,5-triarylbenzene, with no polymeric compound being detected18 (Table 1, entries 1–5).The reaction time required for optimum yields was ca. 3 h in most cases. With the variation in yields given in Table 1, it can be seen that there are important differences in the behaviour of the TCS–EtOH reagent towards aryl methyl ketones.Substituents such as methoxy and phenyl, which increase the negativity of the acetyl group by resonance or inductive effects, retard the yield of b-methylchalcone as shown in entries 4 and 5 [eqn. (1)]. On the other hand, substituted acetophenones having strongly electron withdrawing groups such as nitro groups gave only b-methylchalcones. Thus 3p- or 4p-nitroacetophenone in entries 6 or 7 was treated with a slight excess of tetrachlorosilane in ethanol to afford the b-methylchalcone 11 or 12 respectively in very good yield.Thus the formation of *To receive any correspondence. Table 1 Reaction of aryl methyl ketones with TCS–EtOH Yield Entry Substrate t/h Product (%)a 1 Acetophenone 2 1,3-diphenylbut-2-en-1-one 1 +1,3,5-triphenylbenzene 2 62 34 2 4p-Chloroacetophenone 3 1,3-Bis(4-chlorophenyl)but-2-en-1-one 3 +1,3,5-tris(4-chlorophenyl)benzene 4 64 28 3 4p-Bromoacetophenone 4 1,3-Bis(4-bromophenyl)but-2-en-1-one 5 65 +1,3,5-tris(4-bromophenyl)benzene 6 23 4 4-Acetylbiphenyl 2 1,3-Bis(biphenyl-4-yl)but-2-en-1-one 7 +1,3,5-tris(biphenyl-4-yl)benzene 8 59 32 5 4p-Methoxyacetophenone 2 1,3-Bis(4-methoxyphenyl)but-2-en-1-one 9 +1,3,5-tris(4-methoxyphenyl)benzene 10 58 37 6 3p-Nitroacetophenone 10 1,3-Bis(3-nitrophenyl)but-2-en-1-one 11 77 7 4p-Nitroacetophenone 8 1,3-Bis(4-nitrophenyl)but-2-en-1-one 12 74 aIsolated yields after column chromatography.J.CHEM. RESEARCH (S), 1997 233 a triarylbenzene can be inhibited by slowing the rate of the second aldol condensation with a substituted acetophenone having a strongly electron withdrawing group.Moreover, the reaction in a slight excess of absolute ethanol as solvent ultimately leads to a decrease in the yield of the 1,3,5-triarylbenzene derivatives [eqn. (2)]. The products of the double condensation were obtained either as mixtures of E- and Z-isomers of the b-methylchalcone (entries 1,2,3 and 7) or exclusively as E-isomers (entries 4, 5 and 6).The structural analysis for the cis-and transisomers was carried out by UV absorption and 1H NMR spectral methods. The E- and Z-isomers exhibit remarkable spectroscopic differences which allow the reported structure assignments. The reaction rate and stereochemical course of the double condensation of aralkyl ketones were influenced by such factors as the kind of substituent at the aromatic ring and the molar ratio of the reactants. The mild conditions and simplicity of the operation offer distinct advantages over the reported methods. In principle, it is found that b-methylchalcone derivatives can be easily prepared from readily accessible and cheap TCS in the presence of absolute ethanol at room temperature. Techniques used: IR, UV, GCMS and 1H NMR References: 24 Table 1: Reaction of aryl methyl ketones with TCS–EtOH Table 2: Spectral data of the b-methylchalcones Received, 8th November 1996; Accepted, 20th March 1997 Paper E/6/07611D Reference cited in this synopsis 18 L. J. Mazza and A. Guarna, Synthesis, 1980, 1, 41.