Indian Journal of Chemistry Vol. 49B, February 2010, pp. 203-208 Modern Friedel-Crafts Chemistry. Part 30 1 Facile synthesis of isomeric tri- and tetramethyltetrahydrophenanthrenes via rearranged cycloalkylation of suitably methylated 1-(1- and 2-naphthyl)-3-pentanols Ali Ali Khalaf *a , Hassan A Albar b & Khalid O El-Fouty b a Department of Chemistry, Faculty of Science, Assiut University, Assiut, Egypt b Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia E-mail: khalafal@aun.edu.eg Received 26 March 08 ; accepted (revised) 17 May 2009 Facile methods for the synthesis of isomeric tri- and tetramethyl-tetrahydrophenanthrenes (11, 18, 21, and 27) have been accomplished through rearranged Friedel-Crafts cycloalkylation of naphthylpentanols 1-4, respectively. Thus, treatments with the mild 85% H 2 SO 4 , H 3 PO 4 and AlCl 3 /CH 3 NO 2 catalysts produced 1,1,2-trimethyl-1,2,3,4- tetrahydropenanthrene 11 from 2,2-dimethyl-5-(1-naphthyl)-3-pentanol 1, 3,4,4-trimethyl-1,2,3,4-tetrahydrophenanthrene 18 from 2,2-dimethyl-5-(2-naphthyl)-3-pentanol 2, 1,1,2,2-tetramethyl-1,2,3,4-tetrahydrophenanthrene 21 from 2,2,3- trimethyl-5-(1-naphthyl)-3-pentanl 3 and 3,3,4,4-tetramethyl-1,2,3,4-tetrahydropenanthrene 27 from 2,2,3-trimethyl-5-(2- naphthyl)-3-pentanol 4. Treatment with the strong AlCl 3 catalyst resulted in varying amounts of side products. The starting and final products were characterized by elemental analysis and IR, 1 H NMR and MS data. Keywords: Friedel-Crafts cycloalkylation, carbocation rearrangements, 1,1,2- and 3,4,4-trimethyltetrahydrophenanthrenes, 1,1,2,2- and 3,3,4,4- tetramethyltetrahydrophenanthrenes In continuation of studies on the theoretical and applied aspects of Friedel-Crafts cycloalkylation reaction 1,2 , the behaviour of four new naphthyl- pentanols, namely, 2,2-dimethyl-5-(1- and 2-naphtyl)- 3-pentanols (1 and 2) and 2,2,3-trimethyl-5-(1-and 2- naphthyl)-3-pentanols (3 and 4) under a variety of conditions are explored. Efforts have been taken to find out facile pathways to synthesize some isomeric tri- and tetramethylated 1,2,3,4-tetrahydrophenanth- renes. OH R 1 : 1-Naphthyl, R = H 4 : 2-Naphthyl, R = CH 3 3 : 1-Naphthyl, R = CH 3 2 : 2-Naphthyl, R = H Results and Discussion Synthesis of naphthylpentanols 1-4: These were synthesized by consecutive standard steps. Thus, condensation of 3,3-dimethyl-2-butanone (pinacolone) with 1-and 2-naphthaldehydes gave supposedly trans- or (E)-2,2-dimethyl-5-(1- and 2-naphthyl)-4-penten-3- ones (5 and 6, respectively). Catalytic reduction of 5 and 6 gave the corresponding 2,2-dimethyl-5-(1- and 2-naphthyl)-3-pentanones (7 and 8, respectively). O O 5: 1-Naphthyl isomer 6: 2-Naphthyl isomer 7: 1-Naphthyl isomer 8: 2-Naphthyl isomer Reduction of 7 and 8 with NaBH 4 gave 2,2- dimethyl-5-(1- and 2-naphthyl)-3-pentanols (1 and 2, respectively). Furthermore, addition of CH 3 MgI to 7 and 8 gave the corresponding 2,2,3-trimethyl-5-(1- and 2-naphthyl)-3-pentanols (3 and 4, respectively). Cycloalkylations of naphthylpentanols 1-4: naphthylpentanols 1-4 were cycloalkylated under a variety of conditions applying both Bronested and Lewis acid catalysts. Identification of the products obtained was based not only on spectral (IR, NMR,