Crown compounds all-oxygen

Figure 16. Unsaturated chiral dihydroxy compounds that have been incorporated into fused-ring all-oxygen crown compounds.

For the cyclic, or crown, ethers, see Section 41.3.10.4. There appears to have been no systematic study of multidentate all-oxygen ligand compounds of Mn. 

Two different all-aromatic crowns have been reported ". In 1975, de Jong, Siegel and Cram reported the synthesis of a tri-binaphthyl system in which each oxygen was bound to a naphthalene ring, but aliphatic bridges were used to join the binaphthyl units. Relatives of this compound are discussed further in Sect. 3.13. The synthesis of this molecule (Structure 17, below) was not simple, but was relatively straightforward. An interesting feature of it was the use of ethyl chloroacetate followed by LAH reduction to attach ethyleneoxy units to the naphthol unit. 

The crystals of this compound are tetragonal, space group P4, Z = 2, a = 1822.7, c = 975.7 pm. Extended XAFS data show that the U(III) atoms are interacting with all the crown-ether oxygens (345). 

The nomenclature convention suggested by Pedersen for the simple compounds involves two numbers. The first of these indicates the total number of atoms in the macrocycle. The second number indicates how many heteroatoms are present in the ring. Compound 3 shown above, for example, contains fifteen atoms in the ring, five of which are oxygen. The commonly accepted name for this compound is 15-crown-5 . The three compounds shown below can all be named by this simple rule. 

More than sixty neutral macrocyclic polyethers containing four to twenty oxygen atoms, each separated from the next by two or more carbon atoms, have been synthesized 40, 41) (see Fig. 8). Many of these compounds form 1 1 complexes in which the cation is encircled by the oxygen atoms of the polyether 44, 71). The potassium complex of di-benzo-30-crown-10 (77) consists of a wrap-around structure, where all the oxygen atoms are approximately equidistant from the central... 

---