PUB - Publikationen an der Universität Bielefeld

The synthesis of several centrotriindanes bearing ortho-phenyl groups in the sterically constricted bay regions is described. The classical three-step sequence including twofold cyclodehydration of the corresponding 2,2-dibenzyl-1,3-indanediols afforded an angular difuso-triidane and several all-cis-tribenzo[5.5.5.6]fenestranols equipped with two or four ortho-phenyl groups. In contrast to the construction of these conformationally flexible centrotriindanes, attempts to synthesize ortho,ortho-diphenyl-substituted tribenzotriquinacenes failed due to the increased rigidity of the TBTQ skeleton. The high steric load imposed by the para-terphenyl moieties affects the spirocyclization between 1,3-indanedione and 1,5-di-(para-2 '-terphenylyl)pentadienone, kinetic control of which is critical to access the all-cis-tribenzo[5.5.5.6]fenestrane framework. In contrast, the corresponding tetraphenyl-cis,cis,cis,trans-tribenzo[5.5.5.6]fenestranol is easily accessible.