Large-ring Compounds

This reaction is used in the synthesis of large-ring compounds. 

A spectacular application of the acyloin ester condensation was the preparation of catenaries like 11. These were prepared by a statistical synthesis which means that an acyloin reaction of the diester 10 has been carried out in the presence of an excess of a large ring compound such as 9, with the hope that some diester molecules would be threaded through a ring, and would then undergo ring closure to give the catena compound ... 

Griesbeck et al. successfully transformed w-phthalimidoalkanoates via PET with concomitant decarboxylation and C,C combination leading to medium- and large-ring compounds with yields in the range 60-80%. Thereby, the solvent system acetone/water and K2CO3 employed for the deprotonation of the carboxylic acids were crucial (Scheme 45) [66]. 

Streptomyces nodosus produces natural products such as amphotericin A and B. These are macrocyclic (large-ring) compounds containing numerous (three to seven) double bonds and multiple hydroxyl groups which are usually located on one side of the molecule. Amphotericin B (9.103) and the very similar nystatin (9.104) are antifungal... 

Crown ethers are large-ring compounds containing several oxygen atoms, usually in a regular pattern. Examples are 12-crown-4 (10),61 dicyclohexano-18-crown-6 (11), and 15-crown-5 (12). These compounds have the property62 of forming complexes with positive ions, gen-... 

This interesting reaction is especially useful for the synthesis of medium- and large-ring compounds from dicarboxylic esters, and is effective for ring sizes that cannot be made by the Dieckmann condensation or decarboxylation (Section 18-1 OB). Radical anions formed by addition of sodium to the ester... 

Cyclic ketones containing up to 31 C-atoms in the ring have been prepared from the corresponding dicarboxylic acids. By the Clemmensen reduction (Reaction LVIII. (c)) the ketones have been converted into cyclic hydrocarbons. These large ring compounds are remarkably stable. (H. Acta, 11, 496,670 13,1152 17,78.)... 

Metallacycloalkanes - Synthesis, Structure and Reactivity of Medium to Large Ring Compounds... 

Griesbeck, A.G., Henz, A., Kramer, W., Lex, J., Nerowski, F., and Oelgemoller, M. (1997) Synthesis of medium- and large-ring compounds initiated by photochemical decarboxylation of W-phthalimidoalkanoates. Helvetica Chimica Acta, 80, 912-933. 

In the course of studying these reaction principles, the chemistry of medium and large ring compounds was investigated. This led to the discovery of the transannular reactions [5] which are a fascinating part of chemistry even today. 

Ketene, dichloroketene, and related compounds react with allylic ethers, sulfides, and selenides in a [3.3] sigmatropic rearrangement. This interesting reaction allows the synthesis of a number of medium and large ring compounds by expansion [72] [73] [74]. Dichloroketene has been prepared in situ by slow addi-... 

Whilst yields are generally low, this is a useful method for preparing large ring compounds, including a number of important musk compounds used in perfumes. 

The syntheses of crown compounds invariably rely upon the Williamson ether synthesis, a dated but reliable reaction which is extemely useful in the synthesis of these medium-ring and large-ring compounds.7 The syntheses are usually not discussed in much detail in the literature, since the emphasis in the general area of supramolecular chemistry is on the properties of the target compounds, not on their preparation. It is frequently the case, however, that these apparently conventional syntheses are far from straightforward. 

Figiire9.3. Angle strain, a) Maximum overlap permitted for open-chain or large-ring compounds. (6) Poor overlap for cyclopropane ring. Bent bonds have much p character. 

Large ring compounds can selectively trap ions based on the ability of various ions to fit within a cavity in the large compound. This results in selectivity such as occurs in transport across membranes in biological systems. 

The sterically bulky phosphines (8) have been prepared by the Grignard method from chlorodi(t-butyl)phosphine and chlorodicyclohexylphosphine. In certain iridium(i) complexes, metallation of these phosphines occurs on the terminal olefinic carbon atom. Treatment of a, )-dialkynyl-lithium reagents with chlorodi-(t-butyl)-phosphine gives the diacetylenic diphosphines (9), which form large ring compounds when they form complexes with transition metals. ... 

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