DIASTEREOSELECTIVE REACTIONS OF 1,4-BIS(BROMOMAGNESIO)PENTANE WITH LACTONES AND CYCLIC ANHYDRIDES

Article abstract of DOI:10.1016/S0040-4020(01)80084-3

In the case of aromatic substrates, reactions of 1,4-bis-(bromomagnesio)pentane with lactones and isatoic anhydrides proceed with a remarkable stereochemical preference leading to the formation of the trans isomer.On the other hand, those with 4H-3,1-benzoxazin-4-ones provide mainly the cis isomer and, much more dramatic stereoselectivity has been observed in the cases of phthalic and 1,2-naphthalene dicarboxylic anhydrides.This difference in the stereochemical control of the intramolecular Grignard reaction can be attributed to the chelation between the groups in ortho position of the intermediate oxoalkyl magnesium compound.The alkoxy and the carboxylate seem to have an opposite effect.Furthermore, reactions of 1,4-bis(bromomagnesio)pentane with non-aromatic cyclic anhydrides yield preferentially the trans diastereoisomer.