Aldol-like intramolecular cyclization

Aldol Reactions.— Baldwin has extended the nomenclature for classifying ring-closures to include intramolecular aldol reactions. Observations of the modes of cyclization of polyketonic substrates have shown that, for example, 6-(enolendo)-exo-trig cyclizations are indeed favoured whereas the five-membered version is disfavoured (Scheme 50). Such generalizations may prove powerful aids to recognition of likely pathways that cyclizations may follow when a multitude of cyclization modes are formally possible, and to the evaluation of the likelihood of success in aldol reactions by which complex cyclic targets are prepared. 

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