Problem functional group switching

Theorem. The set of all sequences of reagents that affects a stated functional group switching problem comprises a regular language. 

Figure 5. Functional Group Switching problems solved as in Ref. 10. RCHOEE is the ethoxyethyl ether of a secondary alcohol EVE is ethylvinyl ether.

H. W. Whitlock, A Heuristic Solution to the Functional Group Switching Problem in Organic Synthesis , J. Amer. Chem. Soc. 1976, 98, 3225. 

The stringent conditions required for the reduction of phosphine oxides are incompatible with many functional groups and often cause severe racemisation of the phosphine. Those problems have been largely circumvented by switching to phosphine boranes, as discussed in the next section. 

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