Multistrategic Retrosynthetic Analysis of Gibberellic Acid

249 + 250 after control elements were added as a result of subsequent optimization. In such a long and complex retrosynthetic analysis, it is invariably found that knowledge obtained from the study of the retrosynthetic steps at the lower levels of the EXTGT tree can provide information which influences the selection of steps and intermediates at the upper levels of the tree. This is usually the case either when an impasse is reached at the lower levels or when some particular pathway leads to an especially appealing lower-level sequence. Or, to state matters somewhat differently, there can be an important feedback of information from the lower levels to the upper levels of EXTGT tree analysis in the case of quite complex targets. 

Still another synthetic route to gibberellic acid has been developed which differs from those above in the transforms used to disconnect the various rings, but which also depends on the initial disconnection of ring A (using aldol and carbonyl addition transforms).  

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