%0 Journal Article %A Guindon, Yvan %A Faucher, Anne-Marie %A Bourque, Élyse %A Caron, Valérie %A Jung, Grace %A Landry, Serge R. %D 1997 %T The Exocyclic Effect:  Protecting Group Strategy to Enhance Stereoselectivity in Hydrogen Transfer Reactions of Acyclic Free Radicals %U https://acs.figshare.com/articles/journal_contribution/The_Exocyclic_Effect_Protecting_Group_Strategy_to_Enhance_Stereoselectivity_in_Hydrogen_Transfer_Reactions_of_Acyclic_Free_Radicals/3708183 %R 10.1021/jo971595s.s001 %2 https://acs.figshare.com/ndownloader/files/5798730 %K acyclic substrates %K stereogenic center α %K diastereoselectivity %K Exocyclic %K Strategy %K feasibility %K hydrogen transfer reaction %K steric %K R 1 %K strategy %K discrimination %K diol %K Acyclic Free Radicals %K factor %K substituent %K rationale %K bifunctional %K Hydrogen Transfer Reactions %K Enhance Stereoselectivity %K exocyclic radicals %K analysis %K Protecting %K transition state models %X To enhance the diastereoselectivity of the hydrogen transfer reaction of acyclic substrates bearing 1,2- or 1,3-diols, the feasibility of a strategy employing bifunctional protecting groups has been demonstrated. This strategy is based upon the “exocyclic effect” or the significant improvement of anti-selectivity exhibited by the reductions of substrates in which the two substituents (R1 and Y) at the stereogenic center α to the radical center are linked together. A rationale for the excellent facial discrimination of these exocyclic radicals is offered based on an analysis of transition state models, which considers both steric and electronic factors. %I ACS Publications