Eight-membered carbocycle

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),... 

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. 

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

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). 

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. 

Let s now consider concerted skeletal rearrangements which allow the direct transformation of a sugar structure into a carbocyde. The Claisen rearrangement has been used for the direct conversion of sugar C-glycosides to eight membered carbocycles, respectively. The reaction has precedents in the transformation of 2-methylene-6-vinyl-tetrahydropyrans to cyclooctenone derivatives, a transformation that has been applied in the synthesis of several natural products [54],... 

The bridged oxazocine 132 underwent cleavage of the N-O bond to give the amino, hydroxy-substituted eight-membered carbocyclic ring 133 (Equation 7) <2005W0068457>. 

Vinylogous modes of this rearrangement are also possible. Complex systems can be attained by utilizing a built-in electrophile in an intramolecular ring expansion/alkylation, as shown in equation (35). This kind of cyclization is applicable to seven- and eight-membered carbocyclic ring synthesis and proceeds with approximately 12 1 stereoselectivity, which is due to the more stable, parallel conformation depicted in equation (35). ... 

Metal x-Complexes formed by Seven- and Eight-Membered Carbocyclic Compounds, 4, 353 Nitrogen Groups in Metal Carbonyl and Related Complexes, 10, 115 Nitrosyls, 7, 211... 

This section focuses on the transition metal-catalyzed formation of ring systems using alkynes in the homogeneous phase. Because of the great number of possible products, this survey is restricted to five- and six-membered heterocycles, and six-and eight-membered carbocycles. 

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