SummaryA number of functionalized and chiral macrocyclic polyethers have been synthesized by condensation of the dithallium alcoholate of (R, R)-(+)-tartaric acid derivatives with a, co-dihalides. In this way for instance, the tetracarboxylic [ 181-0, macrocycle 3c and its derivatives become readily available. They form complexes with various cationic substrates. NMR. and crystal-structure data provide information about the orientation of the side chains X in 3 with respect to the macrocycle. It is concluded that in the secondary amides like 3 b and in their complexes the four X-groups are preferentially in an axial orientation on the average. This property is of much significance for the design of molecular receptors and catalysts based on this macrocyclic structure. The preparation of a number of other macrocycles is also described.
The hexacarboxylate [27]-0, macrocyclic polyether (1) is a suitable receptor molecule forming stable and selective inclusion complexes with guanidinium and imidazolium as well as ammonium salts in aqueous solution.GUANIDINIUM groups of arginine residues play a most important biological role as binding sites for anionic substrates in enzyme active sites,' in receptor sites of antibodies,2 and in nucleic acid interaction with the highly charged protamines and his tone^.^ They are also present in hormones (like bradykinin) and in toxins (tetrodotoxin and saxitoxin).* A low molecular weight receptor molecule capable of strongly complexing guanidinium groups would thus be of great interest. The design of such a system also represents an interesting problem in molecular recognition.
Treatment of an alkene with a thallium(i) carboxylate and iodine gives the corresponding vic-iodocarboxylate in high yield. The reactions are regiospecific and in conjunction with solvolysis of the products, offer an alternative to the Prevost reaction. Differences in the behaviour of thallium(i) carboxylates and silver carboxylates towards alkenes in the presence of iodine are discussed.
The action of thallium(1) acetate and iodine on some enol acetates has been examined as a general method for the formation of a-iodo-ketones.a-IODO-KETONES are usually prepared by treatment of a ketone with iodine in the presence of a strong baseJ1 by a sodium iodide exchange reaction with a chloro-or bromo-ketoneJ2 or by the use of N-iodosuccinimide 3 3 4 or iodine(1) chloride3 on the enol acetate of the ketone. The first method suffers from the disadvantages that consistent results are sometimes difficult to obtain5 and that subsequent cyclisation reactions can occur in the presence of a strong base.6 The second method is subject to pronounced steric effects, neither 17-bromo-20-oxosteroids nor 4-bromo-3-oxo-5~-steroids ,' for exampIe, reacting to any appreciable extent. I n the third method N-iodosuccinimide has an advantage over iodine( I) chloride in that it does not attack nuclear double bonds but its formation involves the use of light-sensitive and relatively expensive silver oxide.During a study of the utilization of thallium(1) salts in organic synthesis8 we attempted to substitute the thallium(1) salt of succinimide for the silver salt in the preparation of N-iodosuccinimide (NIS) .3 Although N-thallio-succinimide could be readily prepared as a pale yellow precipitate by the reaction of thallium(1) ethoxide and succinimide, it was very unstable. This was not unexpected since most compounds which contain a thallium-nitrogen bond are very susceptible to hydrol ~s i s . ~ However, while iodination of an enol acetate could be achieved using NIS prepared in situ by the above procedure, it was found more convenient to treat a solution of thallium(1) acetate and an enol acetate with a solution of the halogen in the same solvent.Initial reactions were carried out on the enol acetates derived from heptan-%one. Earlier workers 3710 reported that this ketone afforded a single enol acetate (1) with isopropenyl acetate in the presence of an acid catalyst but more recently it has been shown that the equilibrium mixture of enol acetates prepared by this method contains a mixture of the compounds (1, cis and trans) and (2) in the ratio 94 : 6.11 Treatment of the equilibrium mixture with thallium(1) acetate and
Addition of iodine to an unsaturated thallium(1) carboxylate in ether at 20' gives a convenient procedure for iodolactonization under neutral conditions. The products are predominantly those of kinetic control. INTRAMOLECULAR cyclization of an incipient iodoniumor bromonium ion intermediate with a carboxylate ion is known as ha1ogenolactonization.l The reaction, which provides a useful synthetic method for the conversion of unsaturated acids into halogenolactones, and after hydrogenolysis into saturated lactones, normally requires the use of alkaline solutions or of sodium salts. The use of readily prepared thallium(1) carboxylates and iodine for the high yield conversion of alkenes into the corresponding vic-iodocarboxylates reported in the preceding paper: suggested the extension of their use for halogenolactonization and the possibility of effecting such reactions under neutral conditions.It was found that slow addition of iodine in ether to a stirred suspension of an unsaturated thallium(1) carboxylate in ether a t 20" using a stoicheiometric ratio of 1 : 1 gave high yields of iodolactones. For comparison purposes unsaturated acids which had previously been used H. 0. House, 'Modern Synthetic Reactions,' 2nd edn.,
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