Friedel-craft acylation of ar-himachalene: Synthesis of acyl-ar-himachalene and a new acyl-hydroperoxide

Abstract

Friedel-Craft acylation at 100 °C of 2,5,9,9-tetramethyl-6,7,8,9- tetrahydro-5Hbenzocycloheptene [ar-himachalene (1)], a sesquiterpenic hydrocarbon obtained by catalytic dehydrogenation of α-, β- and γ-himachalenes, produces a mixture of two compounds: (3,5,5,9-tetramethyl- 6,7,8,9-tetrahydro-5H-benzocyclohepten-2-yl)-ethanone (2, in 69% yield), with a conserved reactant backbone, and 3, with a different skeleton, in 21% yield. The crystal structure of 3 reveals it to be 1-(8-ethyl-8-hydroperoxy-3,5,5- trimethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-ethanone. In this compound O-H...O bonds form dimers. These hydrogen-bonds, in conjunction with weaker C-H...O interactions, form a more extended supramolecular arrangement in the crystal. © 2011 by the authors; licensee MDPI, Basel, Switzerland.