Rearrangement conformational effects

Let us examine the stereochemistry of pinacolic deamination in some detail.. In this we shall see the operation of a factor we have not yet encountered in rearrangements conformational effects. More important, we shall get some idea of the methods used to attack problems like this. 

Carbonyl insertion is preferentially observed in the photoindueed reaction of 22 to give the cyclohexenones 25 and 26 as shown in Scheme 9 [17]. The acyl complex 24 is involved as an intermediate. The eyclohexenone formation appears to be susceptible to conformational effect, as observed in the facile rearrangement of 27 to 28. 

Conformational effects on reactivity can be considered under the heading of steric effects,11 though in these cases we are considering not the effect of a group X and that of another group X upon reactivity at a site Y but the effect of the conformation of the molecule. Many reactions fail entirely unless the molecules are able to assume the proper conformation. An example is the rearrangement of N-benzoylnorephedrine. The two dia-... 

Where foe allylic alcohol is in a secondary position, conformational effects or the character of the oxidant can still favor an oxidative rearrangement over simple oxidation to foe ketone (equation 19). ... 

Comparable cis/trans selectivities and similar conformational effects on them were studied in ring enlargements of cyclic sulfonium ylides. ° Rearrangements of sulfur ylides performed in repetition were used for stepwise ring expansion 5- 8—> 11- —> 14- - 17-membered. ° Synthesis applications of... 

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