Retron partial

Additional keying information can come from certain other structural features which are present in a retron- or partial-retron-containing substructure. These ancillary keying elements can consist of functional groups, stereocenters, rings or appendages. Consider target structure 5... 

At the opposite end of the topological spectrum are stereocenters in terminal rings that are eligible for disconnection. Stereocenters in such rings which are elements of a retron or partial retron for a ring disconnective transform should be cleared preferentially by application of that transform. Examples 156, 157 and 158 illustrate such stereocenters (starred). 

Partial Retron. An incomplete retron for a particular transform. 

Applying any reaction to a synthetic target requires knowledge of the retrons that make the reaction applicable at some point in the synthesis. Partial retrons - those keying elements that... 

Partial retrons are more numerous than retrons for the quasi-Favorskii rearrangement. One can focus on the possible carbonyl product and consider all those groups that could be derived from those carbonyl groups. Furthermore, one of the classic partial retrons for a quasi-Favorskii rearrangement is sirrply a tertiary or quaternary carbon embedded in a polycyclic carbon framework. These synthetic strategies will be illustrated with exanples later in this chapter. 

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