Transformations into Carbocyclic Systems

The usual reactions involved in carbocyclic cyclization of the aforementioned open-chain intermediates are aldol and Claisen condensations as well as Michael additions. Some examples of the Wadsworth-Emmons reactions have been also published. 

Processes similar to the conversion of 2 into 312 are the low yield preparation of dihydropinosylvin (318) and its isomer 319 from pyrone 

From the previous discussion, it is evident that intramolecular aldol condensations are commonplace in this field. However, intramolecular Claisen-type condensations can be accomplished by the use of magnesium methoxide, as in the formation of phoroglucinol derivative 328 (70CRV553). The common intermediate 323 (undetermined ionization state) accounts for both formation of 324 through an aldol condensation (C3—C—C/C6) and formation of 328 by Claisen condensation (C3—C—C—C/C5). Further examples of directed cyclizations, depending on the base used, are gathered in the review by Money (70CRV553). 

The presence of adequately placed double bonds allows intramolecular Micheal additions to play an important role in carbocyclic ring formations. 

C3—C—C—C/C5 type and complementary steps. Further examples of intramolecular Michael additions have been described (77AP931 85MI5). 

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