Sesquiterpenoids. Part IX. The origin and structure of α-caryophyllene alcohol: X-ray analysis of the p-bromobenzenesulphonyl ester

Abstract

α-Caryophyllene alcohol is the rearrangement product obtained when humulene, and not caryophyllene, is treated with concentrated sulphuric acid in ether. X-Ray analysis of the p-bromobenzenesulphonyl derivative has established that the alcohol is 1,4,4,7-tetramethyltricyclo[5,3,1,0^2,6]undecan-11-ol, with the stereochemistry shown in (VIIa). The conformation of the cyclohexane ring is of the chair type, with the oxygen substituent axial. The cyclopentane rings exhibit envelope conformations. The bridging valency angle in the bicyclo[3,2,1]octane system (104°) is distinctly smaller than tetrahedral. The crystals are monoclinic, space group P2₁/c, with Z= 4 in a unit cell of dimensions a= 12·65, b= 10·82, c= 16·43 Å, β= 109° 13′. The atomic co-ordinates were obtained by Fourier and least-squares calculations, and the final value of R is 12·6% over 2021 reflections.