Cyclophanes dilution principle

The preparation of thiamacrocycles of the cyclophane type by substitution of thiolates on suitable substrates usually leads to the desired products in good yields [55], favoured by the rigid group principle [56] and by application of the dilution principle [1]. On the other hand yields of conformative flexible thia-cycloalkanes under similar conditions as a rule are not satisfactory and often low... 

Cyclizations by formation of carbon-sulfur-bonds belong to the best studied reactions which use the dilution principle. Usually bromides react with thiols [7 b, 17, 18], thiuronium salts [19], or with sodium sulfide [20] and thioacetamide, respectively. The formation of C—S bonds represents one of the most valuable methods to synthesire medium-membered cyclophanes such as 4-8 [7 b, 18 b, 20d, 21]. 

Cyclizations by formation of carbon—selenium bonds represent a modern method with a high synthetic potential in the chemistry of cyclophanes. Selenocyanates such as 16 are accessible usually in excellent yields through the reaction of bromides with KSeCN [27], The reaction with benzylic bromides under reductive conditions using the dilution principle results in good to excellent yields of [3.3]di-selenacyclophanes which can be deselenized photochemically, pyrolytically (without previous oxidation), or by reaction with arynes, Stevens rearrangement and subsequent reaction with Raney nickel. [2.2]Metacyclophane (18), for example, is accessible in 47% total yield by using this sequence of reactions starting with... 

Rossa, L. and F. Vdgtle (1983) Synthesis of Medio and Macrocyclic Compounds by High Dilution Principle Techniques," in Cyclophanes /, F. L. Boschlee, Ed., Springer-Verlag, Berlin (transl. of Topic Curr. Chem., 113). 

Systems containing Sulphur as the only Heteroatom. - A variety of sulphur-containing cyclophanes were synthesized by the dilution principle, using an improved apparatus. The equipment will prove valuable in the preparation of many macrocyclic systems. The iron-catalysed reaction between bis-(2,4-dimethoxyphenyl) sulphide and S2CI2 gave four macrocyclic systems, including (47). The formation of (47) occurs by the unusual electrophilic cleavage of C-aryl-S bonds. 

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