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The Baldwin rules: revised and extended

The Baldwin rules constitute one of the clearest examples of the success which can be obtained through the application of stereoelectronic concepts to reaction design. With thousands of examples, the predictive power of these rules is inarguable. However, time has revealed a number of exceptions and gray areas within these rules, leading to extensions and revisions. In this review, we will present an overview of how subsequent studies of ring closure have clashed with several of Baldwin's predictions, leading to the revision of some classes of ring closure (alkyne cyclizations, electrophilic closures, etc.). We also discuss for which the original rules were vague (epoxides) or absent (promoted cyclizations), and the evidence revealed since Baldwin's work that has allowed for a better understanding of these ambiguities. With the concise summation of these amendments, this review aims to present an overview of the understanding of cyclization reactions to date. WIREs Comput Mol Sci 2016, 6:487–514. doi: 10.1002/wcms.1261