Cyclization Reactions-Baldwins Rules for Ring Closure

If di- or polyalkylation is a problem, the addition of triethanolamine borate to the reaction mixture will suppress overalkylation. Likewise, enolates formed in the presence of EtjB react smoothly to form mono-alkylation products, as illustrated in the following examples.  

These reactions are subject to stereoelectronic control. The transition state for S 2 displacement requires collinear (180°) disposition of the nucleophile (C ) and the leaving group L. In some cases, for steric reasons, 0-alkylation dominates over C-alkylation. See Section 6.3 below for additional details. 

CYCLIZATION REACTIONS-BALDWIN S RULES FOR RING CLOSURE 

The following facts must be considered in planning intramolecular cyclizations  

An extensive study of known cyclization reactions led J. E. Baldwin to formulate a set of empirical rules to predict the relative ease of ring-forming processes. These 

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