[8+2]-CycIoadditionen mit Benzylidenmalonsäurederivaten: Steuerung der Stereochemie durch die Carbonsäurestrukturteile [1] / [8+2]-C ycloadditions with Benzylidene Malonic Acid Derivatives: The Role of Carboxylic Groups in Stereoselectivity [1]

Abstract
The stereochemistry of the regiospecific [8+2]-cycloaddition of 8 -methoxyheptafulvene (2) with Michael type olefins is elaborated. The stereoselectivities are decreasing in the series a-cyanacrylic acid ester (9), 1,1-dicyanethene derivatives (1), 5-phenylmethylene-1,3-dioxane- 4,6-dione (6 ). The mechanistic impact is discussed. The structure of the tetrahydroazulenes 3-5, 7, 8 and 10, which are formed in good chemical yields are determ ined, mainly by 1H NMR. The molecular structure of 3c is determ ined by X-ray crystallography