Triple Bond Routes to Macrocycles

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Science  07 Jan 2000:
Vol. 287, Issue 5450, pp. 13
DOI: 10.1126/science.287.5450.13d

Many plants and marine organisms make large cyclic molecules that are used as fragrances or drugs. One challenge in developing synthetic pathways to these compounds, especially for target molecules containing double bonds, is closing the ring with the desired stereochemistry and without modifying other functional groups. Unsaturated macrocycles also have attracted attention recently for their electron transfer properties and their potential uses in nanotechnology.

Fürstner et al. show that ring closures of a chain bearing two triple bonds near each end can be effected by tungsten or molybdenum catalysts with yields of 50 to 80%. These macrocyclic compounds contain a single triple bond, which can be converted preferentially via a Lindlar reduction into a double bond with the Z (or cis) configuration as in many natural products. They synthesized the odorous cyclic lactone ambrettolide (musky) and a large building block of the cytotoxic alkaloid nakadomarin A, originally isolated from a marine sponge.

Mayor and Lehn have focused on highly unsaturated macrocycles. In a single step, they were able to couple 4, 6, 8, or 10 subunits through pairs of triple bonds to form macrocycles; the subunits consist of benzene rings each carrying four p-tert-butylthiophenyl groups. These neutral molecules are reversibly reducible at potentials just below -1 volts, and they accept more electrons as more subunits are added without a corresponding increase in the reduction potential. This behavior suggests that larger species could serve as “molecular batteries,” where the additional subunits act like cells in a macroscopic battery.—PDS

J. Am. Chem. Soc.121, 11108 (1999); J. Am. Chem. Soc.121, 11231 (1999).

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