The formation of derivatives of bicyclo[3,2,1]octane in reactions between carbanions and quinones

Abstract

In methanol containing sodium hydroxide the xanthen derivative (II) forms a carbanion that adds (reversibly) trimethyl-1,4-benzoquinone giving a derivative (IVa) of bicyclo[3,2,1]octane. Addition of 2-methyl-1,4-naphthaquinone gives a similar derivative (Xa). The structures and stereochemistry of these compounds have been established by a combination of chemical and n.m.r. spectroscopic methods and (IVa), for example, shown to be (7aR*, 11R*, 11aS*, 13R*, 14R*)-8,11,11a,13,14,15,18-heptahydro-5,11-dihydroxy-6,9,10,11a,13,16,17-heptamethyl-7a(7H),11-o-benzenobenzo[c]xanthen-8,15,18-trione.