Calcium-mediated fulvene couplings. 3. Reductive coupling of guaiazulene with activated calcium to give a mixture of 8,6 ' and 8,8 ' (diguaiazulenide)calcium isomers. Thermal rearrangement of the 8,6 ' isomer to the 8,8 ' isomer and X-ray crystal str

摘要

The reductive coupling of guaiazulene with activated calcium in THF at 30-35 degreesC affords a 60:40 mixture of two isomers, 8,8'-(1) and 8,6'-(2) (diguaiazulenide)bis(tetrahydrofuran)calcium, respectively, in nearly quantitative yield. The isomers were separated and purified by recrystallization. The X-ray crystal structure of 1 is reported. A modest dependence of the isomer ratio on the reaction temperature was noticed. At lower temperature (9 degreesC) the 8,6' isomer, 2, is favored slightly, and at higher temperature (67 degreesC) selectivity for the 8,8' isomer, 1, is slightly enhanced. Thermolyses of each isomer revealed that 1 is the thermodynamically preferred isomer. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 27]