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Diradical versus Concerted Mechanisms for the Dihydroxylation of Protoanemonin by OsO 4 and OsO 4 −NH 3 − The Effect of the Base in the Reaction
Author(s) -
Ujaque Gregori,
Maseras Feliu,
Lledós Agustí
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.200390126
Subject(s) - dihydroxylation , chemistry , diradical , osmium tetroxide , concerted reaction , reaction mechanism , olefin fiber , medicinal chemistry , stereochemistry , photochemistry , computational chemistry , organic chemistry , catalysis , enantioselective synthesis , singlet state , physics , nuclear physics , excited state , electron microscope , optics
The dihydroxylation of a set of monosubstituted olefins [ethene ( 1 ), propene ( 2 ), styrene ( 3 )] and 5‐methylene‐2(5 H )‐furanone [protoanemonin ( 4 )] by osmium tetroxide have been studied by means of DFT (B3LYP) calculations. The effect on the reaction mechanism of the coordination of a base (NH 3 ) to OsO 4 ( 5 ) to form OsO 4 −NH 3 ( 6 ) has been investigated. These calculations show that the activation barriers for the [3+2] concerted mechanisms are lowered by the presence of an amine coordinating the osmium tetroxide, in agreement with experiment. For the dihydroxylation of protoanemonin (an olefin having a stepwise diradical mechanism in the Diels−Alder reaction) both the concerted and the diradical mechanisms have been evaluated. These studies indicate that the dihydroxylation of olefins proceeds through a concerted mechanism, although in the dihydroxylation of protoanemonin the diradical mechanism may play a significant role. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)