Baldwin's rules

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Baldwin's Rules are a series of guidelines outlining the relative favourabilities of ring closure reactions in alicyclic compounds. They were first proposed by Jack Baldwin in 1976.

The rules classify ring closures into exo and endo types, depending on whether attack occurs with a bond breaking outside or inside the ring, respectively. They also classify reactions by the type of electrophilic site: dig, trig or tet, meaning digonal (sp), trigonal (sp2) or tetrahedral (sp3) respectively. Baldwin discovered that orbital overlap requirements for the formation of bonds favour only certain combinations of ring size and the exo/endo/dig/trig/tet parameters.

Baldwin-disfavoured are:

• 3-exo-dig and 4-exo-dig
• 3-endo-trig and 4-endo-trig and 5-endo-trig

[edit] References

• Baldwin, J. E., Rules for Ring Closure, J. Chem. Soc., Chem. Commun. 1976, 734. DOI:10.1039/C39760000734
• Baldwin, J. E., et al, Rules for Ring Closure: Ring Formation by Conjugate Addition of Oxygen Nucleophiles, J. Org. Chem., 42(24), 3846 (1977).