Octalins conformation

The two structures having three gauche interactions are both trana-decalins and were eluted in the order predicted by comparison with the equivalent conformations in the monomethyldecalins. These structures are both directly available through octalin precursors from 1,3-dimethyltetralin ... 

In contrast with the cyclohexanes and the decalins, evaluation of the conformational energies of the octalins seems not to have been attempted by either experimental or theoretical approaches. The experimental equilibria in Table IX permit calculation of the free energy changes for isomerization of the various isomers, but are of little help for estimating the enthalpies unless the corresponding entropy changes can be assessed. 

Examination of the molecular model of A >i -octalin reveals that it can exist in three distinct chair-chair conformations. One modification is a meso form with a plane of symmetry such that one ring is the mirror image of the other it has one twofold axis of symmetry, i.e., a = 2. The other two chair-chair conformations are a dl pair each enantiomer has three twofold axes of symmetry, i.e., v = 4. The chair conformation of Ai> -octalin is a dl pair with no twofold axis of symmetry, i.e., a=l. The chair conformation of chair conformation of trans-Ai.2-octalin is a dl pair with no twofold axis of symmetry, i.e., a=l. These parameters and the differences in conformational energy based on them are collected in Table XXXVIII. 

The striking agreement between the computed intercepts and those obtained by extrapolation of the experimental equilibria suggests that no significant entropy terms have been overlooked. The slopes, AHjR, of the lines joining the computed intercepts with the experimental data points provided a measure of the conformational energy of each isomer relative to A >i -octalin. 

Ganem has described a novel allylic alcohol to haloepoxide transformation (26) (28) using t-butylhypochlorite as the oxidant. This is the first known case where anchimeric participation by the hydroxyhalonium ion, as in (27), is invoked. The reaction, which has an analogy with iodolactonization, is susceptible to conformational and stereochemical requirements, since the octalin (29) gave a low yield of (30). Mild conditions for the preparation of (mostly steroidal) oxirans... 

It is thought that conformationally isomeric carbonium ions may be involved, but more importantly that the counter-ion plays a significant role in determining particularly the octalin ratios. In the case of solvolysis of (368 X = Cl), an ion pair which resembles (373) has chloride ideally placed to abstract a proton from C-10 leading to (371) a relatively small movement of the counterion is needed for Cl to assume a suitable location for abstraction of a C-1 proton. Similar arguments apply if the ion pair has the conformation (374) accordingly the preference for formation of (371) over (370) under kinetic control is rationalized. In acetolysis of (367 X = Cl) the counter-ion in the intermediate (375) is now suitably located for abstraction of a proton from C-1 but not from C-10 this accords well with the preference for formation of (370) over (371) in this system, expressed as a ratio of 4.80 at 70 °C extrapolated to zero time. The... 

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