Regioselective and Stereoselective Transformations of Enantiopure p-Benzoquinone Equivalents.

The selectivities of typical transformations of the p-benzoquinone Diels-Alder adduct 2 and its dihydro derivative 3 are shown to be highly dependent on the mechanistic path followed. To avoid ambiguities and to make sure of clearly defined regioselectivity, the monoketal 13 was examined and proven not only to be an excellent dienophile but, of course, also to lead to reliable regioselectivity in subsequent transformations. This led to the correction of an earlier provisional assignment of the alkylation products 11 and 12.