Eight-membered carbocycles

Michaut A, Rodriguez J. Selective Constraction of Carbocyclic Eight-Membered Rings by Ring-Closing Metathesis of Acychc Precursors. Angew Chem Int Ed. 2006 ... 

The Cope rearrangement is of great importance as a synthetic method e.g. for the construction of seven- and eight-membered carbocycles from 1,2-divinylcyclopropanes and 1,2-divinylcyclobutanes respectively (e.g. 11 12),... 

The structural elucidation of many azacyclooctatetraenes reveals that the tub conformation is the preferred conformation of the eight-membered-ring. As in the case of the carbocyclic analog, the compounds avoid a planar situation with an antiaromatic, 8 n-electron system and exhibit rather normal polyolefinic character. 

Dotz reaction, since both an alkyne and CO are inserted. However, the additional double bond present in the starting complex participates in the subsequent electrocyclic ring closure, giving rise to eight-membered carbocycles. 

Metal TT-Complexes Formed by Seven- and Eight-Membered Carbocyclic Compounds, 4,353... 

Recognizing that intermediates in the [4 + 2]-reaction of dienes and alkynes could be intercepted with components in addition to CO as in the [4 + 2 + l]-reaction, Gilbertson and Evans independently published two new methods for the synthesis of eight-membered carbocycles involving [4 + 2 + 2]-cycloadditions. Saa and co-workers report a... 

The basic structure of taxol is that of a tetracyclic compound -A, B, C and D rings-, in which the central B ring is an eight-membered carbocycle. In principle, the formation of this medium sized ring appears somewhat problematic because of both entropic and enthalpic factors. 

Gilbertson and co-workers were also able to facilitate the rhodium-catalyzed [4-i-2-1-2] carbocyclization reaction with a substrate having an all-carbon tether (Eq. 13). This methodology has been extended to the asymmetric rhodium-catalyzed [4-t 2-1-2] reaction (Eq. 14). Although the exact origin of asymmetric induction was not discussed, the ability to accomplish the asymmetric rhodium-catalyzed [4-i-2-1-2] reaction provides a novel approach to eight-membered ring systems. 

Based on previous success in the Pauson-Khand reaction [43], Evans demonstrated a sequential approach to the synthesis of eight-membered rings, which involved a rhodium-catalyzed aUyhc amination reaction followed by carbocyclization, to effect a three-component couphng (Scheme 12.11). To date, this transformation is only the second example of a sequential rhodium-catalyzed reaction in which only temperature is used to modulate catalytic activity. 

In addition to eight-membered carbocycles, the unusual properties of transition-metal complexes containing 2,2 -diazabiaryl ligands also attracted a good deal of... 

The conformational properties of such eight-membered ring molecules have been reviewed fairly recently (74MI51900). Cyclooctane is the archetypical molecule in this class, and the heterocyclic analogs, such as the azocanes, oxocanes and thiocanes, as well as carbocyclic derivatives, such as cyclooctanone, all have closely related conformational features and a brief overview of their conformations will now be given. 

Unlike carbocyclic and oxygen-containing heterocyclic systems, catalytic enantioselective synthesis of eight-membered ring amines proceeds efficiently and with excellent enantioselectivity. These catalytic ARCM reactions can be carried out in the absence of solvent as well. Representative data regarding cat-... 

Narasaka s chiral titanium catalyst, prepared from (Pr 0)2TiCl2 and a tartrate-derived (2R,3R)-l,l,4,4-tetraphenyl-2,3-0-(l-phenylethylidene)-l,2,3,4-butanetetrol, is utilized for the asymmetric [2+2] cycloaddition of A-acyl oxazolidinones to 1,2-propadienyl sulfides possessing a-substituents, which afford methylenecyclobutane derivatives with high enantiomeric purity. These chiral adducts are readily transformed to seven- and eight-membered carbocycles with chiral side chains by the ring-cleavage reaction and subsequent cationic cyclization of the chiral cyclobutane derivative [68] (Eq. 8A.44). 

This section follows the content of Section 9.02.8 in CHEC-II(1996) without repetition of data presented in the latter but refers to several papers omitted in CHEC-II(1996) along with new publications. Below are presented various synthetic methods, which are classified by the nature and size of the starting ring. Peculiar differences with CHEC-11(1996) should be marked (1) the absence of paragraphs devoted to formation of oxepine derivatives from four- and five-membered carbocycles because new syntheses of these kinds were not found in the literature (2) Sections 13.02.8.2.2, 13.02.8.2.5, and 13.02.8.2.6, which are new, appear concerning with formation of oxepine derivatives from four-, (other) seven-, and eight-membered heterocycles, respectively. 

Raymond E. Dessy and William Kitching Metal 7r-Complexes Formed by Seven-Membered and Eight-Membered Carbocyclic Compounds M. A. Bennett Author Index—Subject Index... 

A method for the synthesis of eight-membered carbocycles based on a new tandem tungsten-catalysed cycloisomerization-cyclopropanation reaction has been reported (Scheme 99).143 This is a catalytic reaction in which a heteroatom-stabilized Fischer... 

Taxol, the anti-cancer compound from yew trees14 (Taxol spp.) has two six- and one eight-membered carbocyclic rings 58. Nicolaou15 saw that two C-C disconnections would give two simple six-membered ring precursors 57 and 59. 

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