The Use of VOF3-TFA

Kupchan and his colleagues were the first to use vanadium oxytrifluoride in trifluoroacetic acid (VOF3-TFA) for the oxidation of tetrahydrobenzylisoquinolines in the synthesis of aporphines and related alkaloids. This significant development has allowed the ready preparation of a variety of aporphines in high yield, and has also provided an insight into possible modes of aporphine biogenesis in plants. 

Oxidation with VOF3-TFA of the nonphenolic iV-formylnorlaudanosine provides in 55% yield the neospirene 15 through the intermediacy of the morphinandienone 14 which undergoes loss of the original C-6 methyl group. 

With laudanosine (16) itself, the reaction takes a different course, and glaucine (17) is produced. This result can best be interpreted in terms of an 

Since morphinandienones were postulated as intermediates in these transformations, it was only fitting that their acid-catalyzed rearrangement also be investigated. Indeed, it was established that they too lead to aporphines via neoproaporphines as shown below in the case of (9-methylflavinantine (18), the catalyst being concentrated hydrochloric acid.  

on the other hand, BFa-ether is used instead of concentrated hydrochloric acid, alkyl shift rather than aryl migration occurs, the ultimate product after catalytic reduction being the alkaloid erybidine (19). (For a further discussion, see Sec. 18.3.3.) 

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