It was found that the reaction of alkyl-substituted aldehydes 1 with benzene, in the presence of 0.5 equivalents of TaCl 5 and 2.5 equivalents of metallic magnesium, at 40 о С for 30 minutes, results in the selective formation of 1,1-diphenylalkanes 2, with high yields of 87 -90% (Scheme 1). To obtain the target 1,1diphenylalkanes 2, a pre-prepared mixture of 0.5 equivalents of TaCl 5 and 2.5 equivalents of metallic magnesium in benzene is required. This mixture of reagents should be allowed to react at room temperature for 30 minutes. Subsequently, aldehyde 1 is added to the specified mixture, and the reaction is heated at a temperature of 40 °C for another 30 minutes to yield 1,1diphenylalkanes 2. The nature of the Lewis acid used greatly influences the nature of the products formed in a reaction. For example, the transformation of octanal at 21 °C in the presence of TaCl 5 or ZnCl 2 in the absence of metallic magnesium is accompanied by the formation of an aldol-croton condensation product 3 with an E-double bond configuration and yields of 55% and 28% for TaCl 5 and ZnCl 2 , respectively. Unusual results were observed when aromatic aldehydes were involved in the reaction. When 4methoxybenzaldehyde was used in the studied reaction, triphenylmethane 4 was formed with a yield of 89% (Scheme 2). Unlike alkyl-substituted aldehydes, complete conversion of 4-methoxybenzaldehyde required boiling the reaction mixture for 6 hours and using 3 equivalents of TaCl 5 and 9 equivalents of Mg.