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Several examples of a new class of lariat ethers, those having steroidal side arms, are reported. These include the following carbon-pivot and nitrogen-pivot structures: 2-(3-dihydrocholesteryloxymethyl)-15-crown-5, mp 61-63 °C; N-(3-cholesteryloxycarbonylmethyl)aza-15-crown-5, mp 85-86 °C; N-(3-cholesteryloxycarbotiylmethyl)aza-18-crown-6, mp 66-67 °C; Ñ-(3-dihydrocholesteryloxycarbonylmethyl)aza-15-crown-5, mp 60-61 °C; jV-(3-dihydrocholesteryloxycarbonylmethyl)aza-18-crown-6, mp 55-56 °C; jV-(3-cholesteryloxycarbonyl)aza-15crown-5, mp 96-98 °C; and jV-(3-cholesteryloxycarbonyl)aza-18-crown-6, mp 82-84 °C. Alkali-metal cation binding by these structures is generally weak, since the macroring binding is not augmented by side arm donor group participation. The high lipophilicity of the side arm does not enhance the cation binding strength. The X-ray crystal structure of one of these novel lariat ethers, N-(cholesteryloxycarbonyl)aza-15-crown-5 has been determined. This is the first example of an uncomplexed, 15-membered crown ether compound containing only nitrogen and oxygen heteroatoms. The macroring structure has one N-C-C-0 torsion angle anti; thus one methylene group is turned inward.

Macrocyclic polyether compounds having one (lariat ethers) or two (bibracchial lariat ethers, BiBLEs) donor-group-bearing side arms exhibit Na+-, K+-, NH4+-, and Ca 2+ -binding affinities and selec tivities different from those of the unsubstituted macrocycles. Mac rocycles utilizing a nitrogen atom as the point of attachment (pivot atom) show generally higher flexibility and binding strength than compounds having the sidearm(s) attached at a carbon (carbon pivot). The more flexible and less polar compounds favor K + over the more charge-dense cations irrespective of hole size. The cation bind ing involves both the macroring and the side arms. This fact is demonstrated for solutions as well as the solid state. Ν-pivot BiBLEs can be prepared by a very convenient single-step cyclization or by a two-step approach that is more conventional but that affords high yields of product. Both lariat ethers and BiBLEs can be electrochemically "switched" to alter the cation-binding affinities and strengths.