Tetracyclines: Communication 20. Configuration of 2- and 3-substituted 10-keto-9-hydroxy-1,2,3,4,4a,9,9a,10-octahydroanthracenes [1,2,3,4,4a,9a-hexahydro-10-hydroxyanthrones], and the stereochemistry of the reduction of naphthoquinone-butadiene adducts with lithium aluminum hydride