Syntheses and Binding Properties of Bibracchial Lariat Ethers (BIBLEs): Survey of Synthetic Methods and Cation Selectivities

Article abstract of DOI:10.1021/jo00376a059

A new, two-step method for the synthesis of 4,10-diaza-15-crown-5 and 4,13-diaza-18-crown-6 and their N,N'-disubstituted derivatives from bis(secondary amines) and 1,2-bis(2-iodoethoxy)ethane is described.Essentially, the method utilizes the incipient sidearms as nitrogen-protecting groups prior to cyclization.The yields for cyclization are high, ranging from 32percent to 77percent.The N,N'-disubstituted derivatives of 4,10-diaza-15-crown-5 produced by alkylation or acylation (A), acylation followed by reduction (AR), cyclization (C), hydrogenolysis (H), or single-step cyclization (O) have the following sidearms: H (H, 91percent), MeOCH2CH2 (C, 38percent), EtOCOCH2 (A, 62percent), PhCH2 (C,72percent), 2-MeOPh (C, 52percent), 2-furanylmethyl (C, 67percent), and 2-nitrobenzyl (A, 50percent).N,N'-Dibenzyl-4,10-diaza-18-crown-6 was obtained by cyclization in 63percent yield.The N,N'-disubstituted derivatives of 4,13-diaza-18-crown-6 produced with the new method have the following sidearms: H (H, 92percent), CO-Et (A, 100percent), n-propyl (AR, 78percent), n-butyl (C, 77percent), n-hexyl (C, 32percent; A, 50percent; O, 7percent), n-octyl (AR, 45percent), CO-n-heptyl (A, 71percent), n-nonyl (O, 11percent;A, 45percent;AR, 39percent), CO-n-undecyl (A, 87percent), n-tetradecyl (AR, 26percent), CO-n-tridecyl (A, 78percent), n-hexadecyl (A, 25percent), n-octadecyl (AR, 60percent), CO-n-heptadecyl (A, 100percent), allyl (O, 26percent), propargyl (O, 22percent), HOCH2CH2 (O, 28percent), MeOCH2CH2 (C, 43percent; AR, 76percent), HOCOCH2 (hydrolysis, 81percent), EtOCOCH2 (A, 92percent), PhCH2 (O, 29percent;C, 66percent), 2-furanylmethyl (O, 27percent, C, 62percent), 2-hydroxybenzyl (A, 85percent), 2-methoxybenzyl (O, 30percent), 2-cyanobenzyl (A, 95percent), 2-nitrobenzyl (A, 90percent), 3-nitrobenzyl (A, 95percent), and 4-nitrobenzyl (A, 70percent).The new cyclization method is compared with other, previously published cyclization reactions with respect to overall yield and ease of purification.When this new cyclization cannot be used, diaza crown ethers can be prepared by alkylation of 4,10-diaza-15-crown-5 or 4,13-diaza-18-crown-6.The homogeneous equilibrium cation binding constants (log K_s) have been determined in anhydrous methanol solution for many of the compounds described herein with Na⁺, K⁺, and Ca⁺.The cation selectivities are rationalized in terms of polar, structural, and lipophilicity effects.