On the reaction of tricarbonyl (4–7-η-1H-1,2-diazepine)iron with activated acetylenes. Preparation of 1-vinyl-1H-1,2-diazepine derivatives

Abstract

Addition reactions of tricarbonyl(4–7-η-1H-1,2-diazepine)iron (2a) to the triple bond of dimethyl acetylenedicarboxylate (DMAD), methyl propiolate (MP), and dibenzoylacetylene (DBA) have been investigated. The stereochemical outcome is influenced by the solvent system and the acetylenic compounds employed. While the reaction of (2a) with DMAD in an aprotic solvent afforded the syn-adduct (3a) as the major product in a protic solvent the reaction resulted in inversion of stereoselectivity to give predominantly the anti-adduct (4a). The reaction of (2a) with MP or with DBA exhibited a similar change in stereoselectivity, although MP has preferential syn selectivity and DBA has high anti-selectivity. The addition reactions of 3-methyl- and 5-methyl-derivatives of (2a) with DMAD have also been studied in order to confirm the mechanism of these reactions. The decomplexation reactions of several adducts have also been studied, with a view to the preparation of 1-vinyl-1H-1,2-diazepine derivatives.