Alder Cycloaddition as a T-Goal

6 Retrosynthetic Analysis by Computer Under T-Goal Guidance. 

10 T-Goal Search Using Tactical Combinations of Transforms... 

Once a particular 6-membered ring is selected as a site for applying the Diels-Alder transform, six possible [4 + 2] disconnections can be examined, i.e. there are six possible locations of the 7i-bond of the basic Diels-Alder retron. With ring numbering as shown in 36, and 

The information obtained by this preliminary analysis can be used not only to set priorities for the various possible Diels-Alder disconnections, but also to pinpoint obstacles to transform application. Recognition of such obstacles can also serve to guide the search for specific retrosynthetic sequences or for the rights priority disconnections. At this point it is likely that all but 1 or 2 modes of 

Estrone (54, Chart 6) contains a full retron for the o-quinonemethide-Diels-Alder transform which can be directly applied to give 55. This situation, in which the Diels-Alder transform is used early in the retrosynthetic analysis, contrasts with the case of ibogamine (above), or, for example, gibberellic acid18 (section 6.4), and a Diels-Alder pathway is relatively easy to find and to evaluate. As indicated in Chart 6, retrosynthetic conversion of estrone to 55 produces an intermediate which is subject to further rapid simplification. This general synthetic approach has successfully been applied to estrone and various analogs.19 

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