Organometallic compounds in organic synthesis. Part 13. Stereoselectivity of complexation of cyclohexadiene esters

Complexation of cyclohexadienes with Fe(CO)3 as the entering group are subject to classical steric hindrance by alkyl groups, but CO2R and related groups introduce a competing factor because they favour sterically the entering group, probably through an intermediate complex. Increase of π-electron availability in the initial 1,4-diene by the attachment of OMe reduces this influence, probably because it favours direct olefin complexation. Non-polar conditions increase the directing effect of CO2R, but complete stereospecificity cannot be achieved except through additional alkyl substitution. Nevertheless, many stereoisomeric pairs can be separated and the route leads to precursors of a number of sterically defined products which are otherwise not readily accessible.