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endo / exo Preferences for Double Bonds in Three‐Membered Rings Including Phosphorus Compounds
Author(s) -
Goumans T. P. M.,
Ehlers Andreas W.,
Lammertsma Koop,
Würthwein ErnstUlrich
Publication year - 2003
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300120
Subject(s) - degree of unsaturation , chemistry , substituent , double bond , ring (chemistry) , stereochemistry , tautomer , ring strain , strain (injury) , medicinal chemistry , organic chemistry , medicine
Depending on the substituent and the heteroelements of an unsaturated three‐membered ring system of the methylenecyclopropane/1‐methylcyclopropene type, the double bond may be preferentially exo‐ or endocyclic. This preference may be considered as a combination of substituent and ring‐strain effects. The substituent effect is a composite one, encompassing both exocyclic olefinic strain and tautomeric preference. The preference for exocyclic unsaturation increases in the order =CH 2 < =NH < =PH < =O for the considered substituents. The higher the ring‐strain, the higher the propensity for exocyclic unsaturation. The low‐strain 2 H ‐phosphirenes favor endocyclic unsaturation, except for the 3‐OH‐substituted species where the strong C=O double bond is the determining factor. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)