Semimasked 1,1 '-diethynylferrocenes: synthetic concepts, preparations, and reactions

Due to the inherent instability of 1,1'-diethynylferrocene, the respective coupling chemistry for the access of oligonuclear systems requires stepwise preparative sequences involving consecutive ethyne deprotection, or the co nversion of latent ethyne precursor functionalities, respectively. The new derivatives 1-acetyl-1'-ethynylferrocene, 3, and, preferably, 1-ethynyl-1'- formylferrocene, 9, turned out to be the most favorable starting compounds. The subsequent synthetic chemistry, as well as the X-ray structures of sel ected starting and target derivatives are presented. A unique intramolecula r coupling product, 12, represents the first ladder-type tricyclic metalloc enophane system exhibiting high ring strain. Supplementary novelties concer ning monoacetylenic parent systems are also presented. (C) 2001 Elsevier Sc ience B.V. All rights reserved.