2-Bicyclo octyl systems

Scheme 2.12 Intramolecular TMM [3+2 cycloaddition to bicyclo[3.3.0 octyl systems...

The same effect is also observed in the bicyclo[2.2.2]octyl system 175f In this system, the effect has been attributed to a substituent induced structural perturbation. The electronegative fluorine and substituent repel each other resulting in enhanced p-character of the endocyclic C-C bonds. The C-F bond order may, therefore, be enhanced as discussed above for the unsubstituted polycyclic fluorides 17S>. 

The first studies in the 2-bicyclo[5.1.0]octyl system were reported by Cope and coworkers . However, they did not measure any reaction kinetics, and product studies were done under conditions where the initial products were not stable. Later in 1969, Friedrich and Wight studied the rates and products of hydrolyses of the endo- and exo-2-bicyclo[5.1.0]octyl 3,5-dinitrobenzoates 87 and 88 in 80% acetone. In contrast to the behavior seen with the [3.1.0]hexyl and [4.1.0]heptyl systems where rates and products are essentially independent of leaving group stereochemistry, the em/o-2-bicyclo[5.1.0]octyl 3,5-dinitrobenzoate (87) reacts 24 times faster than does the exo isomer (88). Both are. 

Generation of a diazonium intermediate (619) from nitrosourea (618) gave products, which are derived from intermediate 620 (equation 161). Surprisingly, in this special case the C(l)-C(2)-bond of the cyclopropane was cleaved. In contrast, diazonium species of a 3-oxa-bicyclo[4.1.0]heptyl or 3,5-dioxabicyclo[5.1.0]octyl system decomposed via an... 

The skeletal rearrangements occurring via an intermediate nonclassical ion 158 are readily detected since they lead to a different, bicyclo[3,2,l]octyl system (cf. with the rearrangement of norbomyl derivatives to norbomyl ones). 

The non-isoprenoid aromatic ester methyl nidorellaurinate (684) has been synthesized. Another non-isoprenoid compound is upial (685), which has been isolated from the marine sponge Dysidea fragilis. It possesses the rare bicyclo[3.3.1]octyl system and possibly it is related to microcionin-4 (686),... 

Charton used his LDR and related equations in the correlation analysis of solvolytic rate constants for 2-exo- and 2-cndb-norbomyl derivatives [(7) and (8), respectively], substituted in positions 1, 4, 5-exo, 6-exo, 6-endo, or 1-anti A delocalized (resonance) electronic effect was found for all but the 4-substituted derivatives. It was suggested that the transition state resembles a classical carbocation rather than the nonclas-sical norbornyl carbocation. Similar treatments for adamantyl and bicyclo[2.2.2]octyl systems found much less indication of a delocalized effect. 

The activation energies for the fragmentation of the carbene in CH2C12 were calculated by the B3LYP/6-31G method to be 14.6, 2.2, and —0.95 for the bicyclo[2.2.1]heptyl, bicyclo[2.2.2]octyl, and adamantyl systems, respectively. Are the product trends consistent with these computational results, which presumably reflect the relative stability of the carbocation formed by the fragmentation ... 

Since evo-2-norbornyl arenesulfonates apparently do solvolyze with anchi-meric assistance, the less strained 2-bicyclo[2.2.2]octyl derivatives (92) are of interest. In this system no comparison of the. rates of exo and endo derivatives can be made, since a substituent exo to one bridge is endo to t fief other. Stereochemical studies are, however, possible. If the carbonium ion (93) were formed from chiral 92 by participation of the —C6 bond, it would be chiral. Scheme 5 shows that attack at C2 of 93 should give retained bicyclo[2.2.2.]octyl solvolysis products (92a), and attack at Cx should give chiral exo-2-bicyclo[3.2.1]octyl... 

Two laboratories, those of Walborsky and of Goering, simultaneously investigated the stereochemistry of solvolysis of optically active bicyclo[2.2.2]-octyl arenesulfonates, and both found that the product consists of only two compounds 2-bicyclo[2.2.2]octyl and exo-2-bicyclo[3.2.1] derivatives.The [2.2.2] system is largely retained although there is some attendant racemization, and the [3.2.1] system is also chiral but again partially racemized. Both groups concluded that ionization at C2 is assisted by the —C6 bond ajH that flip product... 

Work has been reported on the conversion of aldehyde 81, the Diels-Alder cycloadduct of acrolein and cyclopentadiene, to its fully saturated primary alcohol and thereafter to bicyclo[3.3.0]octyl hydrocarbons.133 A silica/alumina catalyst system provides cu-bicyclo[3.3.0]octane, while phosphoric acid and Kieselguhr gives the A2-olefin. Since this cyclic alkene reacts under Koch-Haaf conditions to produce the... 

In other studies, Clark and Smale have investigated the effects of a-phenyl substitution in the solvolyses of endo- and exo-bicyclo[3.1.0]hexyl through [5.1.0]octyl chlorides. For the endo derivatives, where the solvolyses proceed by a favored, concerted disrotatory mechanism in the parent systems, replacement of hydrogen by phenyl gives a relatively small rate enhancement (kph/ H = 1 )- other hand with the exo[3.1.0]... 

A comprehensive NMR spectroscopic study126, of a series of acyclic carbodications was carried out. Carbodications were also observed in more rigid systems, such as the apical, apical congressane dication 57103, bicyclo [2.2.2] octyl dication 65127 and bicyclo [3.3.3] nonyl dication <59106 (manxyl dication — Fig. 10). 

Entries 6-9 and 10-12 illustrate the tendency for rearrangements to occur leading to the most stable cation in each particular system. The tertiary 1-methylcyclopentyl cation is the only ion observed from a variety of precursors containing five- and six-membered rings. The tertiary bicyclo[3.3.0]octyl cation is formed from all bicyclooctyl precursors. As previously mentioned, the tendency to rearrange to thermodynamically stable ions by multiple migrations is a consequence... 

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