Fused carbocyclic

Similarly a marked increase of regioselectivity has been shown in the catalyzed Diels-Alder reactions of the chiral bicyclic lactame 24 (Scheme 3.9) with a variety of dienes [27] (isoprene, mircene, (E,E)-L4-dimethylbutadiene, 2,3-di-methylbutadiene, 2-siloxybutadiene). The catalyzed reactions were more regio-selective and totally enJo-antz-diastereoselective anti with respect to the bridgehead methyl group). The results of the cycloadditions with isoprene and mircene are reported in Scheme 3.9. The cycloadducts have then been used to provide interesting fused carbocycles [28] with high enantiomeric purity as shown in Scheme 3.10. 

A number of intramolecular cycloadditions of alkene-tethered nitrile oxides, where the double bond forms part of a ring, have been used for the synthesis of fused carbocyclic structures (18,74,266-271). The cycloadditions afford the cis-fused bicyclic products, and this stereochemical outcome does not depend on the substituents on the alkene or on the carbon chain. When cyclic olefins were used, the configuration of the products found could be rationalized in terms of the transition states described in Scheme 6.49 (18,74,266-271). In the transition state leading to the cis-fused heterocycle, the dipole is more easily aligned with the dipolarophile if the nitrile oxide adds to the face of the cycloolefin in which the tethering chain resides. In the trans transition state, considerable nonbonded interactions and strain would have to be overcome in order to achieve good parallel alignment of the dipole and dipolarophile (74,266). 

Volumes 3 and 4 cover five-membered rings with two heteroatoms, or more than two heteroatoms, respectively, each with their fused carbocyclic compounds. 

Volumes 5 and 6 cover six-membered rings with one, or more than one, heteroatom, respectively, again with fused carbocyclic compounds. 

Volume 2 Five-membered Rings with One Heteroatom and Fused Carbocyclic Derivatives... 

Other benzo-fused carbocycles could be prepared in moderate yield by a similar strategy. Isomerically pure 3-substituted benzocyclobutenes or 5-substituted tetralins, 211, were prepared by a five-step sequence from the appropriate a-(2-fluorophenyl)-[Pg.101]

This intriguing regioselectivity induced by the fused carbocycle triggered a cascade of papers addressing the question of the electrophilic reactivity of annelated benzenes [2-7], which have continued to flow until nowadays [8-14]. 

Other methods that rely on the use of the carbohydrate template to construct fused carbocycles have been successfully investigated as strategies for the formation of carbocycles from sugars. Chirality transfer from the sugar to the new carbocycle is observed for these reactions. These annulation reactions are the subject of the second part of this section. 

Table 3 Synthesis of Fused Carbocycles, j5,y-Unsaturated Ketones and 3-Cyclopentenols from Diene-Magnesium Reagents...

Because of their aromatic character, pyrones undergo annulation reactions and the introduction of substituents less readily than do most cyclic a,B-unsaturated carbonyl compounds. Nevertheless, some suitable modifications have been developed that allow these compounds to be used effectively in annulation reactions. Some reviews about synthesis of 2-pyrones with 3,4-fused carbocyclic ring systems are currently available (82S337 86G109 92T9111). 

Flash-vacuum pyrolysis has been used in a general annulation protocol for the synthesis of fused carbocyclic and oxacyclic ring systems of type (Tables 1 and 2). The pre-... 

Table 1. Fused Carbocyclic Ring Systems from Flash-Vacuum Pyrolysis of Vinylcyclopropanes...

Table 2. Examples of Fused Carbocyclic and Oxaeyelic Ring Systems Synthesized from Vinylcyclopropanes...

Begley, M. J., Mellor, M., Pattenden, G., New Approach to Fused Carbocycles Intra molecular Photocyclizations of 1,3 Dione Enol Acetates, J. Chem. Soc., Chem. Commun. 1979, 235 236. 

Fused carbocycles can be obtained by this method starting with bicyclic lactones, e.g., 3534. 

Further examples of diaslereoselective cis hydrogenations of fused carbocyclic, as well as heterocyclic ring systems, are given in Table 2. 

The reactivity of substituents on the fused benzene rings of (benzo)pyridazine derivatives was not discussed in CHEC-I because it is little different from that of the corresponding fused carbocycles,... 

A large number of polycyclic heterocycles containing two or more six-membered rings that share two or more carbon atoms are known. For the majority of these systems, only one of the six-membered rings contains the heteroatoms and the other rings are fused carbocyclic rings such as cyclohexane, benzene, naphthalene, and in rare examples, anthracene. Systems in which more than one of the six-membered rings contain heteroatoms are also briefly discussed these include spiro-cyclic compounds and substituted naphthalenes. 

Of the two possible isomers where R = Me, only the transmetallacycle is detectable by NMR. Other alkenes fail to give metallacycles by this method. The reaction also fails with the Nb analog of HI. The metallacycles, IV, are unstable at 25°C and are sensitive to air and water. If 1,7-octadiene is used in place of ethylene in Eq. (e), then metallacycle V, stable below 100°C, is obtained . The fused carbocycle thus aids stability. 

CYC Monocyclic or fused carbocycle containing no benzene rings, optionally substituted by acyclic hydrocarbyl, i.e., any alkyl, alkenyl or alkynyl groups that might be present are included within this Superatom. 

ARY Monocyclic or fused carbocyclic system containing at least one benzene ring. 

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