Macrocycle expansion

WASSERMANN BORMANN Maciocydiclactamsynttwsis Ring expansion sequence of lactams by reaction with cyclic Iminoethers followed by reductive ring opening to a macrocyclic lactam. 

The concept of expansion of the porphyrin macrocycle by formally inserting additional carbon atoms between the pyrrole rings was first considered and synthetically realized by LeGoff/ He also suggested a nomenclature for these macrocyclic systems using the word platyrin which... 

In the previous sections, expanded porphyrins have been described in which the expansion is restricted to the pyrrole-linking bridges. The smallest expanded porphyrin in which the expansion is created by an additional pyrrole subunit in the macrocycle is the so-called orangarin, a [20]pentaphyrin(1.0.1.0.0).13 Orangarin 39 can be prepared via a hydrogen chloride induced... 

The present procedure for ring expansion has also been applied to l,2-bis(trimethylsilyloxy)bicyclo[n.l.0]alkanes, which are prepared by cyclopropanation of l,2-bis(silyloxy)cycloalkenes. The latter are readily available from acyloin condensations in the presence of chlorotrimethylsilane. " This reaction provides a new route to cyclic 1,3-diketones and macrocyclic compounds containing two 1,3-diketone units in the ring. 

Keywords Medium-sized ring lactams. Macrocyclization. Ring expansion. Rearrangement, Fragmentation... 

REMP, the acronym for ring expansion metathesis polymerisation is a special case of ROMP, where the growing polymer chain stays attached to the catalyst at both ends nntil a macrocycle is released. This requires that the active carbene be tethered... 

The bis(trimethylsiloxy)bicyclo[n.l.O]alkane 231 undergoes the FeCl3-induced ring expansion to the cycloalkane-1,3-dione 232. This method has been applied to the synthesis of macrocyclic tetraketones [128]. (Scheme 92)... 

Apart from the biological implications, aspects of the chemistry of macrocyclic ligands are of relevance to a diverse number of other areas. Indeed, there has been a remarkable expansion of research involving these other areas during recent times. Many of the developments impinge on topics such as metal-ion catalysis, organic synthesis, metal-ion discrimination, and analytical methods, as well as on a number of potential industrial, medical and other applications. 

Expansion of tin-containing macrocycles can likewise be performed by Grignard reagents139 (see, e.g., Scheme 18). 

Thus, when one looks sufficiently critically at the ideas currently under discussion one finds that there appears to be no good reason for discarding the conventional tert.-oxonium ion as the propagating species, and that the only clearly identifiable problem is whether propagation through these conventional tert.-oxonium ions goes by the Jaacks mechanism or by the ring-expansion mechanism. This is a difficult matter to resolve experimentally because the direct discrimination between the microcyclic ions (II), (VIII), and (IX) on the one hand and the macrocyclic ion (V) on the other, requires subtle and sensitive techniques. 

Fig. 39 Synthesis of macrocyclic aliphatic polyester by ring-expansion polymerization initiated by cyclic tin(IV) alkoxides...

Kricheldorf HR, Lee S-R, Schittenhehn N (1998) Macrocyclic polymerization of (thio) lactones - stepwise ring expansion contraction. Macromol Chem Phys 199 273-282... 

Like their phosphorus(III) analogues, cycloarsoxanes (RAsO) undergo metal-mediated ring expansion to produce flexible macrocyclic ligands n = 5, 6, 8) that... 

For a review of this reaction, and of other ring expansions to form macrocyclic rings, see Stach, Hesse Tetrahedron 1988, 44. 1573-1590. 

The sulfonamide macrocycle proved to be a hospitable template, and at the same time the sulfonamide functionality bears the possibility of farther derivatiza-tion of [2]rotaxanes (see Section 8.4 Chemistry with Amide-Based Catenanes and Rotaxanes). Furthermore the expansion of the cavity did not afford a change of the blocking group - no disassembly of wheel and axle was detected. 

An attractive application of this strategy can be visualized in the synthesis of the tripeptide segment 136, Scheme 44, present in the macrocyclic antibiotic lysobactin 40, Fig. 4. It was reported that p-lactams 131 and 132, upon ring expansion under the NaOCl-TEMPO conditions indicated above, afford NCAs 133 and 134, respectively. Coupling of the NCA 133 with (S)-LeuOMe results in the formation of 135 which upon exposure to 134 provides tripeptide 136 in high overall yield [122],... 

The use of RuC13 also causes decomposition of the solvent. With such a metal, however, the product of the reaction is H2(OMP) [24]. The carbon monoxide derived from the decomposition of the solvent is added to the macrocycle in a ring expansion reaction generating the porphyrin ring. 

Structural variants of porphyrins obtained by heterocyclic core modification, macrocyclic ring expansion, alteration of structural topology, and incorporation of tailor-made substituents constitute an area of considerable interest. Potentially rich families of conjugated heteroporphyrins with well-defined structures provide an opportunity for implementation in applications in the field of chemistry, biology, and material science. This chapter reports on the synthesis and structural modifications of a number of heteroporphyrins. 

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