Carbocyclizations eight-membered rings

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

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. 

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. 

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-... 

The conformational properties of eight-membered rings linearly fused with two benzene rings have been investigated in some detail by dynamic NMR. The parent carbocyclic compound is (452) which exists as a 1 1 mixture of the chair (453) and the boat (probably... 

Functionalized medium-sized carbocyclic rings (especially seven- and eight-membered rings) can be accessed by this route through the use of the appropriate [3.2.1], [3.3.1], or [4.2.1] oxabicydic substrates. This approach avoids otherwise entropically disfavored cyclization approaches to these rings, and therefore has proven particularly valuable for the syntheses of certain families of natural products. 

Paley and co-workers used enantiopure T -(l-sulfinyldiene)iron(0) tricarbonyl complexes as templates for the enantioselective construction of eight-membered ring carbocycles. 

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