Preliminary research toward the total synthesis of a novel crown ether that is a potential fluorescent chemosensor for potassium ion recognition

The purpose of this research was to synthesize a novel crown ether compound that has been designed to fluoresce with greatly enhanced intensities when in the presence of selected alkali metal cations. The novel crown ether compound (cryptand) 12,25-(1,5 - dimethyloxynaphtho)-1,4,7,10,14,17,20,23-octaoxacyclohexacosane (1) was synthesized through 6 steps. The general synthetic route for the preparation of cryptand 1 is given in the proposed synthetic procedure. Reaction of benzaldehyde (23) with glycerol (24) in the presence of concentrated sulfuric acid afforded cis and traps-1,3-O-benzylideneglycerol (25). Cis and trans-2-O-benzyl-1,3-O-benzylideneglycerol (27) was obtained when 1,3O-benzylideneglycerol (25) was treated with benzyl bromide (26) and sodium wire in benzene. Acid-hydrolysis of the 2-O-benzyl-1,3-O-benzylideneglycerol (27) in methanol gave 2-O-benzylglcerol (28). The key starting material is 12,25-bisbenzyloxy1,4,7,10,14,17,20,23-octaoxacyclohexacosane (31), which requires the formation of four carbon-oxygen bonds. 2-O-benzylglcerol (28) was reacted with triethyene glycol ditosylate and sodium hydride in dioxane. This treatment gave the product 12,25-bisbenzyloxy1,4,7,10,14,17,20,23-octaoxacyclohexacosane likely to be (31) along with the 1:1 and a 3:3 crown ether products. The compound likely to be (31) was treated with H2 and a Pd/Ccatalyst and the resulting compound was 12,25-dihydroxy-1,4,7,10,14,17,20,23Octaoxacyclohexacosane (2). Compound likely to be (2) was reacted with 1,5bis(bromomethy)naphthalene and potassium t-butoxide in tetrahydrofuran to give the final cryptand compound 1. The structures of the crown ethers, the products of this reaction, have not yet been unambiguously assigned.