MECHANISTIC THEORETICAL PROPOSALS FOR: ALKENES BY CLAISEN REARRANGEMENT OF α- ALLYLTHIO CARBENES; AZA-COPE REARRANGEMENT OF 4- BUTENYLIMINIUM IONS; 2- SUBSTITUTED PYRROLIDINE DERIVATIVES; SYNTHESIS OF PERHYDROGEPHYROTOXIN, KEY STEP; PART V; THE ORGANIC CHEMISTRY NOTEBOOK, Nº 13.