Baldwin's rules

Baldwin's rules in organic chemistry are a series of guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds.

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.

For example, cations often disobey Baldwin's rules, as do reactions in which a third-row atom is included in the ring.

A 5-endo-dig ring closing reaction was part of a synthesis of (+)-Preussin:[8] Baldwin's rules also apply to aldol cyclizations involving enolates.

[9][10] Two new descriptors need to be defined: enolendo and enolexo, which refer to whether both carbons of the enolate C-C fragment are incorporated into the ring formed or not, respectively.