Steroid Rearrangements Appearances Can Be Deceptive

Superficially, the following four transformations 1-4 appear to be mechanistically similar. Show that this is not so, and give a mechanism for each transformation. 

Treatment of the hexahydroindolo [2,3-a]qumolizine derivative 1 with dimsyllithium in THF/DMSO gave an excellent yield of the expected diastereomeric p -ketosulphoxides. When the latter were heated under reflux in THF for five minutes in the presence of 6 equivalents of p-TsOH, the eburna derivatives 2a (17%) and 2b (8%) were obtained together with the two isomeric aspidosperma derivatives 3 (14%) and 4 (17%). 

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