Synthesis of Functionalized Cyclophanes by Ring-Opening/Ring-Closure Cascade Reactions of Siloxycyclopropanes

摘要

Our repetitive approach to the synthesis of large-ring compounds has been extended to the preparation of a number of functionalized cyclophanes. The key components are substituted methyl 2-alkenyl-2-siloxycyclopropanecaroxylates, such as 8-10, 24-28,36,and 39, which are easily prepared by a highly versatile route involving malonate alkylations. Treatment of these precursors with cesium fluoride under appropriate conditions of high dilution causes cascade reactions that proceed with consecutive desilylation, ring-opening, proton transfer, and finally,intramolecular Michael addition to afford benzannulated large-ring compounds in generally good yields. The geometry of the aromatic spacer in precursors 8 and 10 does not allow formation of monomerica cyclic products, but the 'dimers' 12 and 13 were isolated in low yield. However, the functionalized cyclophanes 11,29,30,31,33,and 34 are formed in moderate to good yields. The pyridinophane 37,its dimer 38,and [13]pyridinophane 40 (obtainable in excellent yield)may be of particular interest as they could serve as precursors to highly functionalized ligands in supramolecular chemistry.