Diradical versus Concerted Mechanisms for the Dihydroxylation of Protoanemonin by OsO4 and OsO4−NH3 − The Effect of the Base in the Reaction

✍ Scribed by Gregori Ujaque; Feliu Maseras; Agustí Lledós

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 147 KB
• Volume: 2003
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/ejoc.200390126

✦ Synopsis

Abstract

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)